Primary and familial hypoalphalipoproteinemia

Primary and Familial Jane L.H.C.

Third, John Montag,

Michael

Hypoalphalipoproteinemia Flynn, Jack Freidel, Peter Laskarzewski.

and

C.J. Glueck

Our specific aim was to assess within-family clustering of high-density lipoprotein cholesterol (HDLC) levels in kindreds identified through probands with primary hypoalphalipoproteinemia, and to determine whether, and to what degree, familial aggregation of HDLC 5 the tenth percentile represents a heritable trait, familial hypoalphalipoproteinemia. Our probands were selected arbitrarily by virtue of HDLC 5 the age-sex-race-specific tenth percentile as the sole dyslipoproteinemia, with an additional requirement that they be normotriglyceridemic (triglyceride levels < the 90th percentile). The probands were also required to have primary hypoalphalipoproteinemia, not secondary to diseases and/or drugs. Fifteen of the 16 probands were men: 12 were referred because of premature myocardial infarction, angina, or stroke, 2 because of family history of premature myocetdial infarction or stroke, and 2 because of low HDLC observed on routine health examinations. Two of the 16 kindreds exhibited three-generation vertical transmission of bottom decile HDLC. In three kindreds, there was also three-generation vertical transmission of bottom decile HDLC. but top decile triglycerides accompanied bottom decile HDLC in one or more generations. Eight kindreds displayed two-generation vertical transmission of bottom decile HDLC. After excluding probands, there were 11 critical matings (bottom decile HDLC by normal), with 30 living offspring, all of whom were sampled. Of these 30 offspring, 13 had bottom decile HDLC, 17 had HDLC > tenth percentile. The ratio of offspring with bottom decile HDLC to those of HDLC > tenth percentile was 13:17 (0.76/l 1. not significantly different from the ratio of 1 /I, the ratio predictive of a dominant trait, X: = 0.63, P > 0.4. The nearly 1 :l segregation ratio for the group of offspring was not due to the aggregation of sibships with, in general, most of the sibs, or none of the sibs affected: within-family expression of low HOLC was also not sex-linked. The 13 hypoalphalipoproteinemic offspring of 11 critical matings included only two subjects whose bottom decile HDLC was accompanied by top decile triglyceride. Our data suggests that not only (by selection) was low HDLC in the probands the sole dyslipoproteinemia. but that the segregation of low HDLC in offspring of critical matings was primarily accounted for by isolated low HDLC. not by hypoalphalipoproteinemia secondary to hypertriglyceridemia. Familial hypoalphalipoproteinemia is a heritable disorder with a pattern of transmission not significantly different from that expected by a hypothesis of mendelian dominance. Irrespective of the more exact determination of a mode of inheritance of familial hypoalphalipoproteinemia, within-family aggregation of low HDLC as an isolated dyslipoproteinemia was associated with accelerated premature coronary heart disease and stroke in these 16 kindreds.

H

igh-density lipoprotein (HDLC) levels have an independent, highly significant, and inverse relationship to coronary and cerebrovascular disease,‘-” with their major protective effect in atherosclerosis probably mediated by reverse cholesterol transport from the periphery to the liver. In our recent studies of pediatric victims of unexplained stroke and their families, we observed that nine of 11 kindreds had two-generation parent-child proband clustering of depressed levels of HDLC and/or elevated triglycerides.‘,2 We speculated that if high-density lipoproteins protect endothelial cells in vivo in man as they do in vitro,3 then low HDLC levels might predispose chilFrom the Lipid Research Clinic, General Clinical Research Center, and CLINFO Centers, Departments of Medicine, Pediatrics, Lipid Research Division, University of Cincinnati Medicai Center, Cincinnati. Supported in part by the Lipid Research Clinic Contract NOIHV-2-2914L. from the National Institute of Health, National Heart, Lung. and Blood Institute: by the General Clinical Research Center grant RROO068-20; and by the General Clinical Research Center CLINFO Grant RROOO@-I-S. Received for publication August 22. 1983. Address reprint requests io Jane L.H.C. Third, MD, Lipid Research Clinic, University Hospital, University of Cincinnati Medical Center, 231 Bethesda Avenue, Mail Location 540. Cincinnati, OH 45267. Q I984 by Grune & Stratton, Inc. 0026-0495/84/3302-0009$02.00/0 136

dren and adults to endothelial injury with localized thrombosis and atherosclerosis, or fail to facilitate healing of injured endothelium. In subjects L 35 years old, homozygous and heterozygous for an-alphalipoproteinemia (Tangier disease), atherosclerosis is accelerated compared to controls.‘2s’3 Hypoalphalipoproteinemia accompanying cornea1 opacity and familial deficiency of apo Al also appear to be associated with accelerated atherosclerosis.‘4-‘6 Schaefer et al” recently described a kindred where the proband had cornea1 opacification, severe coronary artery disease, and no detectable apo Al. Her two offspring and one brother had HDLC and apo Al levels that were approximately 50% of normal. Since one of the most important determinants of HDLC levels is plasma triglyceride,18 we focused in this report on probands selected by normal trigiyceride levels and primary depression of HDLC levels (5 the tenth percentile) as their sole dyslipoproteinemia excluding hypertriglyceridemic probands whose hypoalphalipoproteinemia might be secondary to hypertriglyceridemia. Previous studies in small groups of subjects by Malloy et a1;19Vergani et al,*’ and Third et al*’ have revealed familial aggregation of individuals with low HDLC and normal triglyceride levels. Malloy et alI9 indicated that “. . . in many kindreds observed by us, the distribution of hypoalphalipoproteinemia suggests a mendelian dominant transmission. At presMetabolism,Vol. 33, No. 2 (February),1984

HYPOALPHALIPOPROTEINEMIA

137

ent, it is indeterminate how many genes may govern the level of HDL in plasma and how many patterns of transmission may exist.” Malloy and co-workers” further noted “. . our clinical experience suggests that, even as a sole identifiable risk factor, severe familial hypoalphalipoproteinemia bears an important association with coronary disease.. . .” Vergani and colleagues” concluded from studies of a single family that ‘I. . the biochemical data and the pedigree are compatible with an autosomal dominant mode of inheritance.” Based in part on our previous recognition of withinfamily clustering of low HDLC,‘*272’-23 our specific aim in the current report was to assess within-family clustering of HDLC levels in families identified through probands with primary hypoalphalipoproteinemia as their sole dyslipoproteinemia, and to determine whether, and to what degree, familial aggregation of HDLC 5 the tenth percentile represents a heritable trait, familial hypoalphalipoproteinemia. MATERIALS AND METHODS Probands and Families Our probands were systematically

collected from patient referrals

Research Center over a 2-year period, with the following proband selection criteria: I. HDLC levels had to be 5 the age-sex-race-specific tenth percentile2“,‘” as the sole dyslipoproteinemia; triglyceride levels had to be CTthe age-sex-race-specific 90th percentile. For entry into the study, the probands also had to have at least two consecutive fasting lipid profiles (usually separated by a 3-week period) meeting the above criteria. The lipoprotein values in the kindred data tables were those obtained at the first sampling. 2. Probands were also required to have primary hypoalphalipoin our outpatient

General

Table 1. Sixteen

Clinical

Hypoalphalipoproteinemic Lipoprotein

Reasonfor Referral

Cholesterol

proteinemia

which was not secondary

progestins.‘”

4. Probands who were diabetic were excluded. 5. Only those kindreds including a hypoalphalipoproteinemic proband and at leasttwo first-degree relatives who could be sampled were included in this study. 6. Probands who had an acute myocardial infarction were studied at feast 5 months after the infarct, since it has been established thaf HDLC levels decrease acutely and remain low for 1 to 2 months following an acute infarct. Table I displays the age, sex, Quetelet index. and lipid and lipoprotein levels of the I6 primary hypoalphalipoproteinemic. normotriglyceridemic probands at initial presentation along with their reason for referral. Twelve of the 16 probands were referred to the General Clinical Research outpatient center because of premature myocardial infarction (MI), angina, or stroke (CVA); and two probands were referred because of a family history of premature myocardial infarction and/or stroke (Table I). Fifteen of the 16 probands were men, most likely reflecting ascertainment bias by virtue of premature coronary heart disease and/or stroke, which develops earlier in dyslipoproteinemic men than in women. None of the hypoalphalipoproteinemic kindreds previously reported by our group as having unexplained pediatric ischemic stroke’,’ are included in this series. and none of the kindreds had previously been identified in our Princeton School District Family Study.22.z’

Lipid and Lipoprotein Determinations After a 12-hour fast, plasma total cholesterol,

Probands: Age, Sex, Total Cholesterol (HDLC. LDLC) (mg/dL).

to androgens,16,”

beta blockers,“’ hypogonadism,” malabsorption,‘8 or liver failure.‘” In addition, although none of the probands or their affected firstdegree relatives were vegetarians, vegetarian probands would have been excluded, given the frequent finding of low HDLC in strict vegetarians.” 3. To be selected for this study as having primary hypoalphalipoprotinemia, the normotipidemic probands had to be free of primary hypertriglyceridemia, and free of secondary hypertriglyceridemia, ie, elevated triglyceride levels secondary to alcohol excess, drugs, and other diseases.‘*

blood was obtained for quantitation of triglyceride, and high- and low-density

(TCI, Triglyceride

(TG). High and Low-Density

height (cm). weight (kg), and Quetelet

Index

Family

Sex

Age

Quetelet w/H2 x 1000

HDLC

LDLC

TC

CVA. age 39

1

M

43

2.12

29

147

208

159

5.08

Ml, age 36

4

M

36

2.86

21

124

185

226

5.90

160/73

Angina, age 48

5

M

49

3.04

32

98

153

115

3.06

150168

TG

LDLCiHDLC

HTlWr cm/kg 192178

Low HDLC on routine health exam

8

F

32

2.72

29

125

166

58

4.31

169177

MI, age 62

11

M

62

2.80

27

137

104

200

5.07

176187

Angina. age 33

14

M

35

2.46

32

163

241

231

5.09

172173

Ml, age 48

15

M

48

2.55

18

141

195

180

7.83

168172

MI, age 57

16

M

61

2.72

29

132

200

194

4.55

175183

MI. age 34

17

M

34

3.17

28

99

160

165

3.54

173195

Ml, age 42

18

M

42

3.97

31

103

169

174

3.32

176/122

Family Hx of premature MI. 19

M

49

2.66

32

158

221

155

4.93

176182

CVA. age 32

CVA

23

M

49

2.80

28

124

180

89

4.42

169/80

Low HDLC on routine health exam

25

M

38

2.71

30

99

169

199

3.30

173/8 1

Family history of CVA

26

M

19

2.48

28

125

174

104

4.46

172173

Angina, age 43

27

M

44

2.40

30

87

132

72

2.90

182178

Angina, age 44

28

M

48

2.83

21

165

224

192

7.86

163/75

THIRD ET AL

138

examined using chi square statistics.3* Segregation analyses were also carried out by sibship size. Similarly, we examined offspring of critical matings of bottom decile HDLC by bottom decile HDLC subjects. We also carried out within-sibship segregation ratio analyses to determine whether the segregation ratio for offspring of critical matings for the overall group was due to the aggregation of sibships with, in general, most of the sibs or none of the sibs affected. Complex segregation and path analysis are being done in this cohort to better define the heritability of low HDLC, and will be the subject of a separate manuscript. The sexes of the affected offspring were systematically tabulated to determine whether this might be a sex-linked disorder.

lipoprotein cholesterol (HDLC, LDLC) following the Lipid Research Clinics’ methodology as previously described.” Lipid Research Clinics and Cincinnati Princeton School District distributions were used to identify subjects with HDLC 5 tenth percentile, and/or triglycerides 2 90th percentile.24,2*lnterday coefficients of variation of HDLC levels in plasma pools containing 50 and 44 mg/dL were 3.7% and 4.2% respectively.

Statistical Methods After excluding probands, the ratio of offspring with HDLC 5 the tenth percentile to those with HDLC > the tenth percentile from critical matings of bottom decile HDLC by normal subjects was

Kindred Table 1 Quetelet

Kindred## #l

l

*

#4

l

*

#5

l

*

#8

l

*

#ll .t

l .

l

Sex

l-l

F

Age

79

l-2

M

65t

II-1

F

46

HDLC

LDLC

196s -

37* -

166 -

4.49 -

2.02

139

37’

121

3.28

2.55

TC

TG

242 186

LDL/HDL

Index

-

M-2, CVA, 39

M

43

208

159

29’

147

5.08

II-3

F

34

252

112

46

184

3.99

2.12 -

U-4

F

45

252

2655

211

II-5

F

43

236

7409

10.

178 -

8.48 -

2.53 -

Ill-1

M

22

150

68

36

100

2.78

2.17

Ill-2

M

14

173

110s

37’

114

3.08

2.17

Ill-3

M

l-l

F

16 -

174 -

84 -

34’ -

123 -

3.62 -

1.81 -

l-2, CVA, 30

M

-

II-1

F

36

153

65

11-2, Ml, 36

M

36

185

226

21’

Ill-1

F

14

192

lll§

40.

Ill-2

F

12

158

79

Ill-3

F

9

73

Ill-4

M

13

-

-

-

72

1.06

2.39

124

5.90

2.86

130

3.25

2.07

40’

102

2.55

1.68

32

34’

33

134 -

88 -

36* -

89 -

-

-

-

68

,971 1.92 -

t

CA

CVA

1.62 -

l-l

F

68t

i-2

M

JV

-

-

-

II-1

F

48

214

119

56

134

2.39

1.89

II-2

M

49

II-3

M

51

153 -

115 -

32’ -

98 -

3.06 -

3.04 -

II-4

M

34

-

-

-

-

-

-

II-5

F

37

-

-

-

-

-

-

Ill-1

F

29

184

121

71

89

1.25

2.52

Ill-2

F

26

149

74

47

87

1.85

3.75

Ill-3

F

24

226

1565

77

118

1.53

2.08

I-1

F

66

l-2

M

67

229 -

205 -

27’ -

161 -

5.96 -

1.91 -

II-1

M

19

150

53

47

92

1.96

-

II-2

F

32

166

58

29’

125

4.31

II-3

F

27

402

143

57

316

5.54

2.72 -

II-4

M

31

165

2495

30’

85

2.83

-

Ill-1

F

l-l

F

69t

148 -

44 -

36. -

103 -

2.86 -

-

CA

l-2

M

J’t

-

-

-

-

-

CVA

Ii-l, Ml, 62

M

62

104

200

27’

137

5.07

64 -

138 -

2.16 -

2.80 -

1

II-2

F

56

211

47

II-3

F

64

II-4

F

57

180 -

66 -

Ill-l

F

27

215

37

54

-

Ill-2

F

19

158

46

61

Ill-3

M

28

160

111

29’

- proband; t = mortality from CA (cancer). CVA (stroke), Ml (myocardial infarct)

= HDLC level _c the age-sex-race-specific tenth percentile.

5 = TG level 2 the age-sex-race-specific 90th percentile. The above notes also apply to the following Kindred Tables 2, 3, and 4.

-

-

-

-

CA

-

CVA

-

-

-

-

2.85

2.34

88

1.44

2.17

109

3.75

2.60

154

139

HYPOALPHALIPOPROTEINEMIA

Of the 16 probands, 15 were male; 14 of the 15 males were adults, as was the single female proband (Table 1). The major referral bias was for premature CHD and/or CVA. Eleven of the 16 probands were referred because of premature coronary heart disease (CHD), cerebrovascular accident (CVA), or angina before age 60 (kindreds 1, 4, 5, 14-18, 23, 27, 28) (Table 1, kindred Tables 1 through 4, Figs. 1 and 2). One proband was referred because of myocardial infarction at age 62 (kindred 11). Two probands, (#I 9, #26) themselves without CHD or CVA before age 55,

RESULTS Probands and Their Families, Study Population

Lipid and lipoprotein levels and Quetelet index (weight [Kg] divided by height2 [cm] x 1,000) for probands and their first-degree relatives, spouses, and families are displayed in kindred Tables 1 to 4, and for probands alone, in Table 1. Figs. 1 and 2 summarize the within-family distribution of bottom decile HDLC, top decile triglyceride, and premature CHD and stroke (CVA) morbidity and mortality.

Kindred Table 2 Kmdred # #14

.i

#15

l

*

816

**

1317

.I

#18

*I

St?X

Age

TC

TG

HDLC

LDLC

19s -

185 -

I- 1

F

73

285

l-2

M

4065 -

11-l

F

73t 36

139

72

57

68

LDLIHDL 9.72

-

II-2

M

35

241

231

32’

163

5.09

2.46

II-3

F

40

209

104

59

129

2.19

ill-1

M

8

130

95§

40”

71

1 78

2.27 -

Ill-2

M

5

157

85

1.47

2.76

F

76

291

II- 1

F

55t 46

203 -

3.08

M

53 -

3.83

l-2

71§ 174 -

58

I-1

194

52

79

105

1.33

2.04

11-2,MI. 48

M

48

195

180

18’

141

7.83

2.55

II-3

M

51

197

80

43

138

3.20

2.09

Ill-l

M

18

169

83

51

101

1.98

2.09

Ill-2

M

17

F

61 -

75 -

1.23 -

l-2

M

47t

28 -

2.39

I-1

142 -

-

-

-

l-3

F

-

-

-

-

55t 73t

l-4

M

II-1

F

73t 62

11-2.MI, 57

M

61

II-3

M

11-4,CVA, 64

F

66t 73

II-5

F

63

II-6

M

Ill-l

M

49t

Ill-2

F

Ill-3

F

I-1

F

l-2

M

l-3

F

l-4

M

II-1

F

52t 29

II-2

F

11-3,Ml, 34

M

Ill-1

Ml

CA

-

-

-

190

157

29’

130

4.48

1.87

200 -

194 -

29* -

132 -

4.55

2.72 -

281

4245

43

143

3.22

258 -

80 -

64 -

178

2.78 -

-

-

-

-

2.27 -

-

32t 34

215

74

43

157

3.65

2.33

18 -

182 -

58 -

37*

133 -

3.59

2.14 -

57t 54

-

-

-

-

182

145§

35’

118

3.37

3.21

33

192

2865

44

91

2.07

3.40

34

160

165

28’

99

3.54

3.17

F

6

158

54

90

1.66

1.60

Ill-2

F

14

1.76

F

2.86 -

l-2

F

50t -

40’ -

72

I-1

130 -

l-3

M

l-4

M

42t

l-5

M

II-1

F

50t 40

11-2.Ml, 42

M

42

II-3

F

37

169 -

174 -

Ill-l

M

18

162

Ill-2

M

14

130

Ill-3

F

12

146

50t

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

31” -

103 -

3.32 -

3.97

83

56

89

1.59

2.71

57

41

78

1.90

2.74

63

72

61

.847

MI Ml

Ml

79 -

3.29

-

Ml

-

24*

-

CA

Ml

152 -

-

CVA CVA

-

133 -

685 86 -

CVA

1.19

2.12

Ml Ml MI Ml

140

THIRD ET AL

Kindred Table 3 Quetelet Kindred #

#19

l

.

#23

**

#25 l *

#26

l

I

t27

**

Sex

I-1

F

l-2

M

l-3

F

l-4

M

II-1

F

Age

W 47t

TC

TG

-

-

-

HDLC

LDLC

LDL/HDL

-

-

Index

-

CVA

-

Ml

44

172

140

38*

106

2.79

2.57

221 -

155 -

32* -

158 -

4.93

2.66

l-2

M

49

II-3

M

II-4

M

57t

Ill- 1 Ill-2

-

-

-

-

-

M

165

99

34

111

3.26

2.41

M

20

182

120

32’

126

3.93

2.37

IIlk

M

17

168

1595

32’

104

3.25

2.52

l-l

F

78

M

59 -

45 -

0.76 -

II-1

F

71t 45

65 -

2.02

l-2

117 156

51

57

89

1.56

2.27

11-2,CVA, 32

2.80

-

M

49

180

89

28*

124

4.42

Ill-1

M

12

153

73

40’

98

2.45

1.62

Ill-2

M

20

182

109

34

126

3.71

2.90

Ill-3

F

22

136

124

43

68

1.58

I-1

F

39

183

66

44

126

2.86

2.43 -

l-2

M

38

169

199

30”

99

3.30

II-1

M

15

151

96

391

93

2.38

II-2

F

16

165

76

46

104

2.26

l-l

F

60

225 -

97 -

459 -

161 -

3.58 -

3.04

170

68

41

6565 -

23” -

2.80 -

2.33

290 -

115 -

l-2

M F

51t 34

II-2

M

41

II-3

M

46

II-4

F

40

II-5

M

42

233 -

1875 -

45 -

Ill-l

M

19

174

104

Ill-2

M

15

175

122

Ill-3

M

10

116

35

IIlk

M

14

I-1

F

74

111 -

104 -

l-2

M

l-3

M

52t

l-4

F

II-1

40t

-

-

-

3.91 -

28’

125

4.46

2.48

38

113

2.97

2.22

43

66

1.53

2.60

35* -

55 -

1.57 -

2.77

-

-

-

-

-

-

-

-

-

MI

3.77 -

3.36 -

-

Ml

2.71 -

151 -

-

MI

Ml

60t 20

II-1

t

-

-

t Ml

-

Ml

-

Ml

F

52t 40

156

80

58

82

1.41

2.48

II-2 Angina 43

M

44

132

72

30,

87

2.90

2.40

Ill-l

F

19

141

57

56

74

1.32

2.26

Ill-2

F

14

118

58

39’

67

1.72

1.97

Ill-3

F

10

129

61

33*

84

2.55

2.05

Cor-bypass

Kindred Table 4 Quetelet Kindred #

#28

l

*

sex

ACE

TC

TG

-

-

l-l

F

78

HDLC

LDLC

-

-

LDL/HDL

Index

t

-

-

CVA.64

II-2

M

II-1

F

64t 48

182

67

47

122

2.60

1.71

224

192

21’

165

7.86 -

2.83 -

II-2 Angina 44

M

48

II-3

M

II-4

F

1st 58

-

-

-

F

54

-

Ill-l

M

23

179

77

47

Ill-2

F

21

139

85

301

Ill-3

M

16

165

65

Ill-4

PA

12

150

80

II-5

TBC = tuberculosis

-

-

TBC, 18

-

117

2.49

2.38

92

3.07

3.03

35

117

3.34

2.27

32”

102

3.19

2.31

-

HYPOALPHALlPOPROTElNEMlA

I

+1

+41 II

Ill

l 51

II

Ill

+8l 1

II

+18

2

3

4

I

Ill

Fig. 1. Kindreds identified by normolipidemic. normotriglyceridemic probands whose sole dyslipoproteinemia was a primary reduction of HDLC i the age-sex-race-specific tenth percentile.

were referred because of premature CHD and/or CVA before age 65 in parents and/or siblings. Two probands (#S, #25) were referred because of asymptomatic depression of HDL cholestero1 detected during “routine” laboratory evaluation. By selection, all of the probands had “normal” triglyceride levels (Table 1, Figures 1 and 2) arbitrarily defined as being below the age-race-sex-specific 90th percentile, with low HDLC levels as their sole dyslipoproteinemia. Moreover, as displayed in Table 1, only two of the probands had triglyceride levels above 2pO mg/dL; all had triglyceride levels below 235 mg/dL. After identifying probands, extensive efforts were made to sample all spouses and all first- and seconddegree relatives. Of 72 living first-degree relatives of

the probands, 60 (83%) were sampled. Their lipids, lipoproteins, and Quetelet indices are displayed in kindred Tables 1 through 4; the families are depicted in Figs. 1 and 2. Of the 60 living first-degree relatives sampled, 27 (45%) had HDLC 5 the tenth percentile, 12 (20%) had triglyceride 2 the 90th percentile. None of the 27 hypoalphalipoproteinemic first-degree relatives were known diabetics requiring insulin, oral hypoglycemic agents, or dietary therapy. Table 2 displays summary statistics for age, Quetelet index, lipids, and lipoproteins for the 16 probands with primary hypoalphalipoproteinemia and their first-degree male and female relatives. As summarized in Table 2, overall, this is a young population, with a median age of probands being 43 and median age of first-degree male and female relatives respectively

142

THIRD ET AL

+I8

I

227

4 I

+28

+23 I

I I

Table 2. Mean, Median, Range, and Standard (HDLC,LDLC),

Total Cholesterol

Deviation for Age, Quetelet

(TC). Triglyceride

Nypoalphalipoproteinemia,

Quet

HDLC

LDLC

TC

TG

LDL’JHDLC

FHA probands

Index. High- and Low-Density

and the Ratio of LDLC/HDLC

and for Their 25 Male and 35 Female First-Degree ”

Age

(TG) (mg/dLJ,

MeWI

Fig. 2. Kindreds identified by normolipidemic, normotriglyceridemic probands whose sole dyslipoproteinemia was a primary reduction of HDLC _c the age-sex-race-specific tenth percentile.

Median

Minimum

Lipoprotein

Cholesterol

for 16 Probands with Primary Relatives Maximum

Std. Deviation

16

43

43

19

62

1St0 male relatives

25

19

17

5

51

9.7

1st o female relatives

35

34

27

1

79

23.7

FHA probands

10.8

16

2.77

2.72

2.12

3.97

0.41

1st o male relatives

21

2.42

2.38

1.62

3.77

0.44

1St0 female relatives

26

3.75

0.48

FHA probands

2.29

2.22

1.60

16

28

29

18

32

1st’ male relatives

25

40

38

23

61

9.2

1st’ female relatives

34

45

43

10

77

15.6 24.5

FHA probands

4.2

16

127

125

87

165

1st- male relatives

24

101

102

66

138

19.8

1st’ female relatives

33

121

104

33

316

56.7 35.1

FHA probands

16

180

177

104

241

1St0 male relatives

25

164

162

116

290

32.3

1St0 female relatives

35

191

160

73

402

65.6

FHA probands

16

158

170

58

231

53.9

1St0 male relatives

25

108

83

28

656

117.6

1St0 female relatives

35

135

80

32

740

139.2

FHA probands

16

4.73

4.51

2.90

7.86

lstO male relatives

24

2.62

2.64

1.23

3.93

0.82

1.49

1St0 female relatives

33

3.02

2.78

0.76

9.72

2.01

HYPOALPHALIPOPROTEINEMIA

being 17 and 27. The probands, as a group, generally were not particularly obese, with their median Quetelet index being 2.72, below the 75th percentile24 (Table 2). Median Quetelet indices in the probands’ first-degree male and female relatives, 2.38 and 2.22 respectively, were about the 75th and 50th percentiles for age.” As displayed in Table 2, median HDLC in the probands was 29 mg/dL; median HDLC levels in first-degree male and female relatives were respectively 38 and 43 mg/dL, both about the 25th percentile.‘4 As displayed in Table 2, the median triglyceride in the probands was 170, (below the 75th percentile24) while median triglyceride levels in first-degree male and female relatives were about the 75th and 50th percentiles, 83 and 80 mg/dL. By selection in probands, and as observed in their first degree relatives, low HDLC was the predominant dyslipoproteinemia, without hypercholesterolemia or broadly distributed hypertriglyceridemia (kindred Tables 1 through 4, Figs. 1 and 2). Median LDL cholesterol in the probands (125 mg/ dL) was < the 50th percentife24 (Table 2); LDLC was about the 50th percentile24 in first-degree male and female relatives. For the probands, the mean ratio of LDLC/HDLC was markedly elevated (4.73), with mean population values being about 3.0;35first-degree male and female relatives had values near the population mean (Table 2). Heritability of Bottom Decile HDLC: As displayed in Figs. 1 and 2, two of the 16 kindreds exhibited three-generation vertical transmission of bottom decile HDLC where subjects with bottom decile HDLC were free of top decile triglyceride (kindred #8 and #17). In three kindreds, #s 1, 14, and 26, there was also three-generation vertical transmission of bottom decile HDLC, but top decile triglycerides accompanied bottom decile HDLC in one or more generations (Figs. 1 and 2). Eight kindreds displayed two-generation vertical transmission of bottom decile HDLC (kindred #s 4, 1 I, 16, 19, 23, 25, 27, and 28), and three had no vertical transmission of bottom decile HDLC. After excluding probands, there were 11 critical matings (bottom decile HDLC by normal), with 30 living offspring, all of whom (loo%), were sampled. Of these 30 offspring, 13 had bottom decile HDLC, 17 had HDLC > the tenth percentile. The ratio of offspring with bottom decile HDLC to those with HDLC > the tenth percentile was 13/17 (0.76/l), not significantly different from I/ 1, the ratio predictive of a dominant trait, X: = 0.53, P > 0.40. In this group of 30 offspring of I1 critical matings, segregation ratio

143

analyses by size of sibships were carried out in five sibships of size 2; four sibships of size 3; and two sibships of size 4. In the five sibships of size 2, the observed ratio of affected to normal (3/7), did not differ significantly from that expected (5/5), Xf = 1.6, P > 0.2; in the four sibships of size 3, the observed ratio of affected to normal (4/8), did not differ significantly from that expected (6/6), X: = 1.3, P > 0.2; in the two sibships of size 4, the observed ratio of affecteds to normal (6/2), did not differ significantly from that expected (4/4), X: = 2.0, P > 0.1. After excluding probands, the 13 hypoalphalipoproteinemic offspring of these 11 critical matings included only two subjects whose bottom decile HDLC was accompanied by top decile triglyceride levels. Moreover, in the 17 offspring from these 11 critical matings who had normal HDLC, only two had isolated top decile triglyceride levels. Our data suggests that the nearly 1/ 1 ratio of affected to nonaffected offspring of critical matings was primarily accounted for by isolated low HDLC, not by “secondary” hypoalphalipoproteinemia, secondary to a defect in the metabolism of triglyceride enriched lipoproteins. The possibility that a few sibships with a large number of affected offspring were responsible for the segregation ratio was tested by performing segregation ratio analyses within the 11 sibships of size 2 or greater arising from the 11 critical matings (affected by normal). In five sibships of size 2 (after excluding the probands), two sibships had no subjects with HDLC 5 the tenth percentile, three had one subject with HDLC 5 tenth percentile, and no kindreds had both subjects with HDLC 5 tenth percentile. These observations were not significantly different from those expected, assuming autosomal dominant transmission, (50% of sibships to have one affected and one normal, 25% to have two affected, and 25% to have two normal), (Xi = 1.80, P > 0.4). After excluding probands, in offspring from the 11 critical matings, there were four sibships of size 3, of which one had no affected (bottom decile HDLC) subjects, two had one affected subject, and one had two affected subjects. This observed finding did not differ significantly from that expected by a hypothesis of mendelian dominance, Xi = 1.33, P > 0.7. There were only two sibships of size 4 originating from the 11 critical matings, one of which (#4) had all four siblings affected, and the second had two of four siblings affected. This observed finding did not differ significantly from that expected by a hypothesis of mendelian dominance, Xi = 1.64, P > 0.8. After excluding probands, we examined the proportion of hypoalphalipoproteinemic family members who were men and women. Of 27 first-degree relatives with

144

THIRD ET AL

bottom decile HDLC, 11 were male and 16 female, strong evidence against sex linkage. Overall, studies of offspring of critical matings, studies of sibships from critical matings, and studies of the associations of bottom decile HDLC with sex suggested that the nearly l/l (0.76/l) segregation ratio for the group was not due to the aggregation of sibships with (in general) most of the sibs or none of the sibs affected, and, moreover, was not sex-linked. The segregation analyses gave results that were not significantly different from those expected by a hypothesis of mendelian dominance. There were four critical matings of bottom decile HDLC subjects by bottom HDLC decile spouses, with all of their nine offspring sampled. After excluding probands, the ratio of those offspring with low HDLC (5 tenth percentile) to those with normal HDLC, 6/3 (2.00), was not significantly different from 6.75/2.25 (3.00), the ratio expected by virtue of an autosomal dominant trait (X: = 0.33, P > 0.5). Here we arbitrarily assumed that the potential homozygote could not be phenotypically distinguished from the heterozygote by HDLC levels. The frequency of hypoalphalipoproteinemia in the spouses seemed quite high, emphasizing the relatively nonspecific nature of bottom decile HDLC as a genetic marker by itself, in the absence of detailed studies of kindred members. Low-Density Lipoprotein Cholesterol and Triglycerides

in Kindreds

In seven kindreds having some subjects with top decile triglyceride levels, there were also other family members with low-density lipoprotein cholesterol (LDLC) levels 1 the age-sex-race-specific 75th percentile. Thus, in kindred #I, there were four subjects with hypertriglyceridemia, and two with top decile LDLC (U-3, 11-4) (kindred Table 1). In kindred #4, subject III-1 had top decile triglyceride and LDLC. In kindred #S, subject II-3 had markedly elevated LDLC, while subject II-4 had top decile triglyceride levels. In kindred #14, subjects I-l and II-2 had top quartile LDLC, and three subjects had top decile triglyceride levels (kindred Table 2). In kindred #16, there was one subject with marked hypertriglyceridemia (II-4), and two with top quartile LDLC (II-5 and 111-3) (kindred Table 2). In kindred #19, subject III-2 had top quartile LDLC, and another subject (111-3) had endogenous hypertriglyceridemia (kindred Table 3). In kindred #26, subjects 111-l and III-2 had top decile and top quartile LDLC respectively (kindred Table 3). DISCUSSION

In the 16 kindreds of this study identified by normolipidemic, normotriglyceridemic probands whose sole dyslipoproteinemia was a primary reduction of HDLC 5 tenth percentile, there was marked within-

family clustering of bottom decile HDLC levels. The findings of three-generation vertical transmission of bottom decile HDLC levels in two of the 16 kindreds; two-generation vertical transmission of bottom decile HDLC in eight of the kindreds; and, in offpsring of critical matings, a nearly l/l ratio of those with bottom decile HDLC to those with HDLC above the tenth percentile, altogether suggested a heritable trait. Moreover, the nearly l/l segregation ratio for the group of offspring was not due to the aggregation of sibships with, in general, most of the sibs or none of the sibs affected. The within-family expression of low HDLC was also not sex-linked. Congruent with our preliminary observations,*’ with those of Vergani et aI,*’ and with the general observations of Malloy and Kane,” the current study suggests that familial hypoalphalipoproteinemia can be transmitted as a heritable disorder, with segregation analyses not significantly different from those expected by a hypothesis of Mendelian dominance. Moreover, our observation of a nearly l/l ratio of affected to nonaffected offspring from critical matings was similar to that of Berg’s,36where eight of 19 offspring from seven critical matings of hypoalphalipoproteinemic by normal subjects had hypoalphalipoproteinemia, a ratio consistent with autosomal dominant transmission. Further explication of patterns of heredity in our hypoalphalipoproteinemic kindreds will require complex segregation analysis and path analysis,” evaluations which are underway. In population groups,‘8 and in kindreds identified by hypertriglyceridemic probands, one of the most important determinants of HDL cholesterol is plasma triglyceride, due to the replacement of cholesteryl esters by triglycerides in the HDL core domains. Within this frame of reference,‘8a38we selected normotriglyceridemic, normolipidemic probands whose sole (primary) dyslipoproteinemia was bottom decile HDL cholesterol. We made these selection criteria to try to identify kindreds where the low HDLC was overtly the primary dyslipoproteinemia, in contrast to primary hypertriglyceridemia accompanied by a “secondary” defect, namely, depressed HDLC. Our data suggests that not only (by selection) was low HDLC in the probands a primary dyslipoproteinemia, but that the segregation of low HDLC in offspring of critical matings was primarily accounted for by isolated low HDLC, not hypoalphalipoproteinemia secondary to hypertriglyceridemia. Thus, the 13 hypoalphalipoproteinemic offspring of 11 critical matings (hypoalpha by normal) included only two subjects whose bottom decile HDLC was accompanied by top decile triglyceride. Moreover, in the 17 offspring from these 11 critical matings who had normal HDLC, only two had isolated top decile triglyceride levels. We speculate

145

HYPOALPHALlPOPROTElNEMlA

that hypoalphalipoproteinemia in our 16 kindreds was a primary metabolic defect, and not secondary to a defect in the metabolism of triglyceride enriched lipoproteins. The metabolic verification of our (above) postulation would necessitate steady state metabolic turnover studies with labeled very low density and high density lipoproteins, studies which are beyond the scope of the current study. We recognize that our identification of “hypoalphalipoproteinemia” by levels less than tenth percentile is entirely arbitrary, and that in the strictest “genetic” sense, one might expect to identify mendelian disorders at even greater extremes of the distribution, perhaps below the fifth or first percentiles for HDLC, mimicking the presence of familial hypercholesterolemia in subjects with LDLC 2 the 95th and/or 99th percentile.39 Irrespective of the more exact determination of the mode of inheritance of familial hypoalphalipoproteinemia, within-family aggregation of low HDLC as an isolated dyslipoproteinemia is associated with accelerated premature coronary heart disease and stroke in these 16 kindreds, as well as in those previously reported,“-” and as in our recent reports of pediatric victims of unexplained ischemic stroke.‘,* Familial hypoalphalipoproteinemia should be added to the rapidly expanding group of hereditary disorders of HDL cholesterol and apolipoprotein Al metabolism, including Tangier disease,‘2,‘3 fish-eye disease,14 HDL deficiency with planar xanthomas,16 familial deficiency of apolipoproteins Al and C3,15 and cornea1 opacification associated with an absence of plasma lipoprotein Al.” Unlike these aforementioned disorders, most of which appear to be transmitted as autosomal recessive traits, and are often found in small inbred communities, familial aggregation of low HDLC may be much more common, and may be transmitted as an autosomal dominant trait in some kindreds.‘9m2’s36 In our I6 kindreds, we have not had the opportunity to determine apolipoprotein Al and A2 levels, and/or to carry out studies of apolipoprotein Al and A2 polymorphism, to assess whether, in addition to the low levels of HDLC, there were any abnormalities of apolipoprotein A 1, or significant apolipoprotein modifications such as observed in the Al-Milan0 apoprotein.“0.4’We speculate that polymorphism of Al and/ or A2 may be more common than is currently recognized, particularly in families with heritable clustering of low HDLC and premature CHD. In seven of the 16 kindreds, the presence of top decile triglyceride in some subjects, and top quartile and/or top decile LDLC levels in others, raises the diagnostic possibility of familial combined hyperlipidemia, a disorder in which multiple lipoprotein phenotypes (IIA, JIB, and IV) occur in the same family.4’

Historically, many individuals identified as having familial combined hyperlipidemia came from families with hypertriglyceridemic probands4* in comparison to our current study, where the normotriglyceridemic probands’ sole lipoprotein defect was bottom decile HDLC. Mean HDLC levels in subjects identified as having familial combined hyperlipidemia are higher than those in subjects having familial hypertriglyceridemia.42 Some individuals with familial combined hyperlipidemia do have bottom decile HDLC levels, although these are very rarely their sole lipoprotein defect, since they usually have elevations of LDL and/or VLDL cholesterol concurrent with depressions of HDL cholesterol.4’ Thus, it is possible that familial combined hyperlipidemia might have been present in some of the kindreds of the current study, where elevated LDLC and triglycerides were noted in family members. Since the “marker” used in this study, HDLC levels, is a general and nonspecific one, it is possible that, in the future, use of more specific markers for dyslipoproteinemias and dysapolipoproteinemias might reveal considerable genetic heterogeneity in families characterized by primary depressions of HDLC in probands. In addition, since many of the probands in this study are relatively young, and since familial hypertriglyceridemia often has a delayed phenotypic expression4’ younger family members currently with normal triglyceride levels might express hypertriglyceridemia when they become adults. In normolipidemic, normotriglyceridemic subjects, whose sole dyslipoproteinemia is a primary depression of HDLC, we do not yet have enough longterm data to know whether weight loss (where indicated), initiation of exercise programs, and/or cessation of smoking will lead to significant increments in HDL cholesterol. In a group of patients whose low HDLC levels were accompanied by elevated triglycerides and the type IV phenotype, Witzum and colleagues43 have previously reported that triglyceride-lowering therapeutic diets may often not be accompanied by increments in HDLC levels. We hope to report in the future the outcome of longterm dietary, exercise, and smoking interventions in individuals whose sole familial dyslipoproteinemia is low HDLC. REFERENCES 1. Glueck CJ, Daniels SR, Bates S. et al: Pediatric victims of unexplained stroke and their families: familial lipid and lipoprotein abnormalities. Pediatrics 69:308-3 16. 1982 2. Daniels SR, Bates S, Lukin R, et al: Cerebrovascular arteriopathy (arteriosclerosis) and ischemic childhood stroke. Stroke 13:360-365, 1982 3. Tauber JP, Cheng J, Gospodorowicz D: Effect of high and low density lipoproteins on proliferation of cultured bovine vascular endothelial cells. J Clin Invest 66:696-708, 1980

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4. Gordon T, Castelii WP, Hjortland MC, et al: High density lipoproteins as a protective factor against coronary heart disease, Framingham Study. Am J Med 62:707-714, 1977 5. Miller NE, Thelle DS, Forde OH, et al: The Tromso Heart Study. High density lipoprotein and coronary heart disease; a prospective case control study. Lancet 1:965-967, 1977 6. Rhoads GG, Gulbrandsen CL, Kagan A: Serum lipoproteins and coronary heart disease in a population study of Hawaii-Japanese men. N Engl J Med 294:293-298,1976 7. Miller GJ, Miller NE: Plasma high density lipoprotein concentration and development of ischemic heart disease. Lancet I: 16-l 9, 1975 8. Takamatsu S, Henmi K, Mizuno S, et al: Studies on the influence of serum lipoprotein and hypertension in cerebrovascular disorders. Jap J Med 16:148-150, 1977 9. Rossner S, Kjellin KG, Mettinger KL, et al: Dyslipoproteinemia in patients with ischemic cerebrovascular disease. Atherosclerosis 30: 199-209, 1978 10. Taggart H, Stout RW: Reduced high density lipoprotein in stroke: relationship with elevated triglyceride and hypertension. Eur J Clin Invest 9:219-221, 1979 Il. Nikkila E: Studies on lipid-protein relationships in normal and pathological sera and effect of heparin on serum lipoproteins. Stand J Clin Lab Invest 5:1-101,1953 12. Herbert PN, Gotto AM, Fredrickson DS: Familial lipoprotein deficiency (abetalipoproteinemia, hypobetalipoproteinemia and Tangier disease), in Stanbury JB, Wyngaarden JB, Fredrickson DS, (eds): The Metabolic Basis of Inherited Disease. New York, McGraw-Hill, (4th ed), 1978, p 544 13. Schaeffer EJ, Zech LA, Schwartz DE, et al: Coronary heart-disease prevalence and other clinical features in familial high density lipoprotein deficiency (Tangier Disease). Ann Int Med 93:261-266,198O 14. Carbon L, Philipson D: Fish-eye disease. A new familial condition with massive cornea1 opacities and dyslipoproteinemia. Lancet 8 149:922-924,1979 15. Norum RA, Lakier JB, Goldstein S, et al: Familial deficiency of apolipoproteins AI and CIII and precocious coronary artery disease. N Engl J Med 306:5 13-5 19, 1982 16. Gustafson A, McConathy WJ, Alaupovic P, et al: Identification of lipoprotein families in a variant of human plasma apolipoprotein A deficiency. Stand J Clin Lab Invest 39:377-387, 1979 17. Schaefer EJ, Heaton WH, Wetzel MC, et al: Plasma apolipoprotein Al absence associated with a marked reduction of high density lipoproteins and premature coronary artery disease. Arteriosclerosis 2: 16-26, 1982 18. Myers LH, Phillips NR, Have1 RJ: Mathematical evaluation of methods for estimation of the concentration of the major lipid components of human lipoproteins. J Lab Clin Med 88:491-505, 1976 19. Malloy MJ, Kane JP: Hypolipidemia. Medical Clinics of North America 66:469-484, 1982 20. Vergani C, Bettale G: Familial hypo-alpha-lipoproteinemia. Clin Chim Acta 114:45-52, 1981 21. Third J, Montag J, Flynn M, et al: Familial hypoalphalipoproteinemia. Circulation 66(Suppl 2):2-60, 1982 22. Laskarzewski PM, Khoury P, Morrison JA, et al: Prevalence of familial hyper- and hypolipoproteinemias-The Princeton School District Family Study. Metabolism 31:558-578, 1982 23. Laskarzewski PM. Khoury P, Kelly K, et al: Prevalence of familial hyper- and hypolipoproteinemias in blacks-The Princeton School District Study. Preventive Medicine 11:142-161, 1982 24. The Lipid Research Clinics Population Studies Data Book (Vol 1). The Prevalance Study. NIH Publication #80-1527, 1980 25. Morrison JA, Khoury P, Mellies MJ, et al: Lipid and

THIRD ET AL

lipoprotein distributions in black adults: The Cincinnati Lipid Research Clinic’s Princeton School Study. JAMA 245:939-942, 1981 26. Glueck CJ, Stein EA, Kashyap ML: Persistent hypoalphalipoproteinemia during therapy of familial type V hyperlipoproteinemia. Artery 5:463-472, 1979 27. Applebaum-Bowden D, HaITner S, Hazzard W: Increase in hepatic triglyceride lipase with Stanozolol. Circulation, 64(Suppl 4):4-590, 1981 28. Hirvonen E, Mal Konen M, Manninen V: Effects of different progestogens on lipoproteins during post-menopausal replacement therapy. N Engl J Med 304:56@563, 1981 29. Tanaka N, Saiaguchi S, Oshige K, et al: Effect of chronic administration of propanolol on lipoprotein composition. Metabolism 25:1071-1075, 1976 30. Mendoza SG, Osuna A, Zerpa A, et al: Hypertriglyceridemia and hypoalphalipoproteinemia in azoospermic and oligospermic young men: relationships of endogenous testosterone to triglyceride and high density lipoprotein cholesterol metabolism. Metabolism 30:481-486, 1981 31. Sacks FM, Castelli WP, Donner A, et al: Plasma lipids and lipoproteins in vegetarians and controls. N Engl J Med 292:11481151,1975 32. Glueck CJ: Classification and diagnosis of hyperlipoproteinemia, in Rifkind BM, Levy RI (eds): Hyperlipidemia, Diagnosis and Therapy. Grune and Stratton, New York, NY, 1977, pp 17-41 33. Manual of Laboratory Operation. Lipid Research Clinics Program (Vol 1). Lipid and Lipoprotein analysis. DHEW Publication (NIH 75-678). US Government Printing Office, Washington, DC, 1974 34. Snedecor GW, Cochran WG: Statistical Methods, (6th ed), Ames, Iowa, Iowa State University Press, 1956 35. Morrison JA, Khoury P, Laskarzewski P, et al: Hyperalphalipoproteinemia in hypercholesterolemic adults and children. Tram Assoc Amer Physicians 93:230-243, 1980 36. Berg W: Genetic influence on variation in serum high density lipoprotein, in Gotto AM, Miller NE, Oliver MF, (eds): High Density Lipoproteins and Atherosclerosis. Elsevier North Holland Biochemical press, Amsterdam-New York, 1978, pp 207-211 37. Rao DC, Laskarzewski PM, Morrison JA, et al: The Cincinnati Lipid Research Research Clinic Family Study. III. Familial determinants of plasma uric acid. Human Genetics 60:257-261, 1982 38. Morrison JA, Khoury P, Laskarzewski PM, et al: Intrafamilial associations of lipids and lipoproteins in kindreds with hypertriglyceridemic probands: The Princeton School Family Study. Circulation 66:67-76, 1982 39. Kwiterovich PO, Fredrickson DS, Levy RI: Familial hypercholesterolemia (one form of familial type II hyperlipoproteinemia). J Clin Invest 53:1237-1249, 1974 40. Franceschini G, Sirtori CR, Capurso A, et al: A-milano apoprotein-decreased high density lipoprotein cholesterol levels with significant lipoprotein modifications and without clinical atherosclerosis in an Italian family. J Clin Invest 66:892-900, 1980 41. Weisgraber KH, Bersot TP, Mahley RW, et al: A-I Milan0 apoprotein. Isolation and characterization of a cysteine-containing variant of the A-I apoprotein from human high density lipoproteins. J Clin Invest 66:901-907, 1980 42. Brunzell JD, Albers JJ, Chait A, et al: Plasma lipoproteins in familial combined hyperlipidemia and monogenic familial hypertriglyceridemia. J Lipid Res 24:147-155, 1983 43. Witztum JL, Dillingham MA, Giese W, et al: Normalization of triglycerides in Type IV hyperlipoproteinemia fails to correct low levels of high density lipoprotein cholesterol. N Engl J Med 303:907-914.1980