Familial concordance of pancreatic function in cystic fibrosis

274

Clinical and laboratory observations

The Journal of Pediatrics August 1989

Familial concordance of pancreatic function in cystic fibrosis M a r y C o r e y , MSc, P e t e r Durie, MD, D a v i d Moore, MD,* G o r d o n Forstner, MD, a n d Henry Levison, MD From the Division of Gastroenterology and The Research Institute, The Hospital for Sick Children, and the Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada

Patients with cystic fibrosis have great variability in the clinical severity of lung disease and digestive problems. Ten to fifteen percent have sufficient endogenous production of pancreatic enzymes to allow normal growth and nutrition, without the need for oral pancreatic enzyme replacement therapy. Endogenous pancreatic enzyme secretion in these patients ranges from normal levels to only 1% to 2% of normal values, 1 indicating that a relatively low level of pancreatic enzyme secretion may be sufficient to avoid steatorrhea. Patients with CF and pancreatic sufficiency have less severe lung disease and a better overall prognosis than the 85% to 90% of patients who have pancreatic insufficiency requiring supplemental enzymes for digestion) With the recent development of relatively simple measures of pancreatic function, based on the level of pancreatic enzymes in serum, it has become easier to characterize the pancreatic function of CF patients? Clinical observation suggests that CF siblings in the same family tend to have a similar degree of pancreatic dysfunction. Because the patients with pancreatic sufficiency have a better prognosis, and because any familial trend may be related to variation of the CF gene, we examined the results of pancreatic function testing in families with more than one CF patient, to assess the degree of concordance within families. Close concordance within families may be of importance in genetic counseling and in understanding the pathogenesis of the disease. METHODS Using the data base established at the Hospital for Sick Children,4 we identified 83 families in which two or more Supported by grants from the Canadian Cystic Fibrosis Foundation. Submitted for publication Nov. 7, 1988; accepted Feb. 24, 1989. Reprint requests: Mary Corey, M. Sc., Cystic Fibrosis Research Centre, McMaster Building, Room 3036, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada, M5G 1X8 *Now at the Division of Gastroenterology, The Adelaide Children's Hospital, Adelaide, Australia.

siblings with CF had been treated within a 20-year period, 1969 to 1988. There were 73 CF sibling pairs, 7 families with 3 CF siblings, 2 with 4, and 1 with 5. Included in the patient group studied were 6 sets of twins--3 male and 3 female. Adopted and half siblings were excluded. The diagnosis Of CF in all siblings was confirmed by sweat chloride levels >60 mmol/L and supported by clinical findings of pulmonary disease, gastrointestinal disease, or both. Patients were classified as having pancreatic sufficiency or insufficiency on the basis of one or more of three tests of pancreatic function. In the majority of patients, pancreatic status was assessed by performing fecal balance studies. This involved a 3- to 5-day stool collection, accurate weighing and recording of daily dietary fat intake, and analysis of fecal fat losses by the method of van der Kamer et al? Patients were considered to have pancreatic insufficiency if fecal fat output, expressed as a percentage of

CF FEVI

Cysticfibrosis Forcedexpiratory volume in 1 second

]

dietary fat intake, exceeded 7%, or 15% in the case of infants less than 6 months of age. 6 The second method involved a quantitative pancreatic stimulation test, carried out according to a previously described method. 7 Duodenal contents were collected through a double-lumen nasoduodenal tube during an 80-minute procedure. After a 20minute equilibration period, pancreatic secretion was stimulated with a continuous intravenous infusion of secretin and pancreozymin for 1 hour. Stimulated enzyme output was corrected according to the fractional recovery of an infused nonabsorbable marker. Output of all enzymes was expressed in units pe r kilogram of body weight per hour. We previously established the relationship between fecal fat balance studies and data obtained from the pancreatic stimulation test. t Fat malabsorption caused by Pancreatic insufficiency is associated with colipase output of <100 U/kg/hr,~so we were able to classify patients into sufficient and insufficient groups. The third method of exocrine

Volume I 15 Number 2

Clinical a n d laboratory observations

275

Table. Classification of families according to pancreatic function status of C F siblings Pancreatic function

Number of CF siblings in family

A g e at diagnosis*

Index case

Subsequent c a s e

2

3

4

5

Total families

PI PS pS~-,-PI PI

PI PS PS-~PI PS~PI

40 7 1 4

5 0

1 1

0 I

46 9 1 4

PS-*PI

PS

2

2

PI

PS

1

1

Index c a s e

4 mo 3 rno 10 yr 2 yr 2 yr 3 mo 7 yr 10 mo

Subsequent c a s e

2 mo 3 mo 7 mo 2 ITIO 2 mo 5 mo 9 yr 5 yr

P1, Pancreatic insufficiency;PS, pancreaticsufficiency.

*Age at diagnosisof CF (index case, subsequentcase) is givenwhere pancreaticsufficiencyand insufficiencywere both seen within a family. pancreatic assessment involved the measurement of serum levels of immunoreactive pancreatic cationic trypsinogen. Random blood samples were drawn and the sera separated by centrifugation and stored at - 7 0 ~ C until analysis. Serum cationic trypsinogen was measured by means of double-antibody radioimmunoassay according to the method of Geokas et al. 8 We previously showed that a serum trypsinogen level <16.6 ~zg/L, the lower limit of normal, is a highly reliable indicator of pancreatic insufficiency in C F patients, but only after the age of 7 years? In this study, 94% of older C F patients with documented fat malabsorption had serum trypsinogen values less than the normal range. Five patients were considered to have pancreatic insufficiency solely on the basis of having had meconium ileus at birth. Three of these were infant girls who were from different families and who died; one set of twin boys moved to another city soon after birth. Although the connection between meconium ileus and pancreatic insufficiency has not been defined precisely, it is rare to find a patient with C F and meconium ileus in whom pancreatic insufficiency does not develop. 9 Individual patients were classified into three groups: those with pancreatic insufficiency, those with pancreatic sufficiency, and a third group with pancreatic sufficiency when first tested but with subsequent pancreatic insufficiency during follow-up. Families were analyzed according to the status of pancreatic function in the siblings. The Fisher exact test was used to assess the association of pancreatic function status in index and subsequent siblings at the time of the study. The Pearson correlation coefficients between index and subsequent sibling values were computed for continuous variables: age at diagnosis, sweat chloride level (the definitive diagnostic test), and FEV~ at ages 10 and 15 years to characterize pulmonary function.

The Student t test was used to compare group means, which are presented as mean _+ SD. RESULTS Of the 83 families available for analysis, there were 63 in whom assessment of pancreatic function was complete in all C F siblings. In the remaining 20 families, one or more of the siblings did not have any record of pancreatic function testing, generally because a sibling had died or a family had moved away before the introduction of standard testing procedures. In the Table, the 63 families are classified according to the pancreatic function status of the siblings. At the time of the study, 60 (95%) of 63 families were concordant for pancreatic status. The Fisher exact test, applied to the first two siblings in each family, showed that the association of pancreatic status in index and subsequent siblings was highly significant (p <0.0001). The eight families with more than two affected siblings showed no discordance. There were 46 families with pancreatic insufficiency (including all six sets of twins), nine families with pancreatic sufficiency, and one family in which pancreatic insufficiency in both sisters developed during follow-up. In six other families, one sibling had pancreatic sufficiency at the time of diagnosis of CF, but pancreatic insufficiency developed during follow-up. In four of these families the index C F sibling had had pancreatic insufficiency since diagnosi s . In the other two families, pancreatic insufficiency has developed in the patient with the index case, but the subsequent C F sibling continues to have pancreatic sufficiency. In only one sibling pair was there complete disagreement in pancreatic function status. The sibling with the index case had pancreatic insufficiency; C F was diagnosed at the age of 10 months, with a 3-month history of failure to thrive but no pulmonary symptoms. Fecal fat excretion

276

Clinical and laboratory observations

was 43% of dietary intake. The diagnosis was made in his older brother 2 years later, at the age of 5 years; he had a 12-month history of productive cough but no digestive problems. Fecal fat excretion was 6% of intake, and he did not require enzymes. This family has moved to another city, so follow-up pancreatic function testing has not been possib!e. Age at the time of diagnosis of C F was significantly correlated for index and subsequent siblings (r = 0.58, p <0.0001), ranging from neonatal to 19 years in both groups, with diagnosis made in 50% of index and subsequent cases, before the ages of 8 months and 4 months respectively. There was a weak correlation in the diagnostic sweat chloride level of sibling pairs (r = 0.23, p <0.03), and a moderate correlation in the pulmonary function of those sibling pairs for whom FEV~ was available at age 10 years (r = 0.52, p <0.01, n = 26) and at age 15 years (r = 0.51, p <0.01, n = 25). Diagnosis was made significantly later in patients with pancreatic sufficiency than in thos e with pancreatic insufficiency (5.9 + 5.6 vs 1.7 + 3.2, p <0.001). However the mean age at the time of pancreatic function testing did not differ in the two groups for any of the three methods of testing. Fecal fat balance was studied in all 79 siblings in 37 families, and in 11 addtional patients whose siblings had other tests. The mean age at the time of testing in these 90 patients was 8.7 _+ 7.7 years, a reflection of the fact that although this test is now done routinely at the time of diagnosis, many older patients were evaluated later in the Course of their disease. Serum trypsinogen results after the age of 7 years were available for all 83 siblings in 41 families, and in 17 additional patients, but there were only 10 families in which there was no other test of pancreatic function. The mean age at time of testing was 16.6 _+ 5.5 years. This test has been available only since 1981, so the majority of patients have been tested many years after diagnosis. Pancreatic stimulation was tested in five sibling pairs and 11 additional patients, at an average age of 10.7 + 9.2 years. This test was always done after other tests. Results of all 'three pancreatic function tests were always in agreement in individual patients except in those in whom pancreatic insufficiency had developed later. This event was always confirmed by more than one test. DISCUSSION This study shows almost universal agreement in the degree of pancreatic exocrine involvement of CF patients within the same sibship. Late development of pancreatic insufficiency, which was observed in a small number of patients; may in fact be more common than was previously believed but may remain undetected because of delay in the diagnosis of CF in the absence of failure to thrive. In

The Journal of Pediatrics August 1989

three of four families in which pancreatic insufficiency developed in th e second sibling during follow-up, diagnosis of CF was made after 2 years of age in the index sibling with pancreatic insufficiency. Waters e t a l . 1~also reported the late development of pancreatic insufficiency in patients whose CF was diagnosed by neonatal screening. In the eight families with discordance in pancreatic function status at first evaluation, pancreatic insufficiency has subsequently developed in all the siblings of five families. We have now undertaken annual reassessment of serum trypsinogen values in all patients with pancreatic sufficiency to monitor longitudinal changes in pancreatic function. Although CF patients with pancreatic sufficiency do not have steatorrhea, they generally have abnormalities of pancreatic secretion. Over a wide range of pancreatic aeinar function, as measured by stimulated enzyme output, they have significantly decreased fluid output and increased protein concentration, lj which in turn may predispose them to ductal obstruction and progressive acinar destruction. Whether pancreatic obstruction and subsequent destruction are progressive in all CF patients with pancreatic sufficiency is not known. We have performed sequential pancreatic stimulation tests in 24 patients with pancreatic sufficiency; the results suggest that those in whom pancreatic insufficiency develops have significantly lower pancreatic acinar function when first tested than those in whom insufficiency does not develop? 2 We conclude that genetic factors may influence the degree of pancreatic disease and possibly its rate of progression. Pancreatic insufficiency and pancreatic sufficiency may represent distinct phenotypic expressions of CF, possibly reflecting variant forms of the C F gene. Some of the families in this study have been included in genetic investigations in our center, in which the haplotype distribution of three DNA probes very close to the CF locus have been analyzed23 A different distribution of haplotypes was found among CF chromosomes from patients with pancreatic sufficiency compared with those with pancreatic insufficiency, indicating that different forms of the disease may have derived from different mutations in the CF locus. The correlations of sweat chloride level and pulmonary function were significant between siblings but were far from predictive. This finding may reflect real genetic variants of the disease that are affected by environmental or measurement factors. Alternatively, it may reflect familial similarity unrelated to the CF gene.

REFERE'NCES 1. Gaskin KJ, Durie P, Lee L, Hill R, Forstner G. Colipase and lipase secretion in childhood-onset pancreatic insufficieney~

Volume 115 Number 2

2.

3.

4.

5.

6.

7.

delineation of patients with steatorrhea secondary to relative colipase deficiency. Gastroenterology 1984;86:1-7. Gaskin K, Gurwitz D, Durie P, Corey M, Levison H, Forstner G. Improved respiratory prognosis in patients with cystic fibrosis with normal fat absorption. J PEDIATR1982;100:85762. Durie PR, Forstner GG, Gaskin K J, et al. Age-related alterations of immunorcactive pancreatic cationic trypsinogen in sera from cystic fibrosis patients with and without pancreatic insufficiency. Pediatr Res 1986;20:209-13. Corey ML. Longitudinal studies in cystic fibrosis. In: Sturgess J, ed. Perspectives in cystic fibrosis. Proceedings of the 8th International Congress in Cystic Fibrosis. Mississauga, Ontario, Canada: Imperial Press, 1980:24.6-55. van der Kamer JH, ten Bokkel Huinink H, Weyers HA. Rapid method for the determination of fat in feces. J Biol Chem 1949;177:347-55. Fomon S J, Ziegler ER, Thomas LN, Jensen RL, Filer LJ. Excretion of fat by normal full-term infants fed various milks and formulas. Am J Clin Nutr 1970;23:1293-313. Durie PR, Gaskin K J, Corey M, Kopelman H, Weizman Z, Forstner GG. Pancreatic function testing in cystic fibrosis. J Pediatr Gastroenterol Nutr 1984;3(suppl):S89-S98.

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8. Geokas MC, Largman C, Brodrick JW, Johnson JH. Determination of human pancreatic cationic trypsinogen in serum by radioimmunoassay. Am J Physiol 1979;236:E77-E83. 9. Lands L, Zinman R, Wise M, Kopelman H. Pancreatic function testing in meconium ileus in cystic fibrosis: two case reports. J Pediatr Gastroenterol Nutr 1988;7:276-9. 10. Waters D, Dorney S, Gruca M, Brown J, Gaskin K. Pancreatic sufficiency in CF infants from a neonatal screening programme. 10th International Cystic Fibrosis Congress Abstracts. Amsterdam: Excerpta Medica, 1988:162. l 1. Kopelman H, Durie P, Gaskin K, Weizman Z, Forstner G. Pancreatic fluid secretion and protein hyperconcentration in cystic fibrosis. N Engl J Med 1985;312:329-34. 12. Durie P, Corey M, Forstner G, Laufer D, Moore D, Cleghorn G. Longitudinal changes in exocrine pancreatic function in cystic fibrosis patients with pancreatic sufficiency: evidence for deterioration of pancreatic function. 10th International Cystic Fibrosis Congress Abstracts. Amsterdam: Excerpta Medica, 1988:161. 13. Kerem B, Buchanan JA, Durie P, et al. D N A marker baplotype association with pancreatic sufficiency in cystic fibrosis. Am J Hum Genet (in press).

Hereditary xanthinuria with severe urolithiasis occurring in infancy as renal tubular acidosis and hypercalciuria Robert D, Fildes, MD From the Department of Pediatrics, Georgetown University Medical Center, Washington, D.C,

Infantile urolithiasis, although not rare, is seldom associated with an underlying metabolic disorder? Type 1 (distal) renal tubular acidosis, in particular, generally occurs as failure to thrive in infancy without the urolithiasis described in older children, adolescents, and adults) Likewise, urolithiasis secondary to hereditary xanthinuria has rarely been reported in infancy? This autosomal recessive disorder of purine metabolism, most often secondary to xanthine oxidase deficiency, is characteristically associated with nephrolithiasis; however, almost all of the reported cases of renal stones have been in adults and older children. The following case illustrates the occurrence of hereditary xanthinuria and nephrolithiasis masquerading as type 1 R T A , with hypercalciuria, calcium stones, and poor weight gain, in a infant.

Submitted for publication Dec. 27, 1988; accepted Feb. 15, 1989. Reprint requests: Robert D. Fildes, MD, Department of Pediatrics, Georgetown University Medical Center, 3800 Reservoir Rd., N.W., Washington, DC 20007.

CASE REPORT

A 7-month-old Kuwaiti girl was rcferred to the nephrology service at Georgetown University Medical Center, Washington, D.C., for evaluation of urolithiasis, hyperchloremic metabolic acidosis, persistent emesis, poor weight gain, and one documented episode or urinary tract infection. At 3Y2 to 4 months of age she reportedly first passed several small, yellowish brown stones into her diaper. She had had repeated episodes of emesis starting shortly after birth and was hospitalized at 5 months of age in I

RTA

Renal tubular acidosis

I

Kuwait for this symptom. Culture of a urine specimen, obtained after urinalysis showed microscopic hematuria and amorphous phosphate crystals, suggested Escheriehia coli infection. She was treated with trimethoprim-sulfamethoxazole, which was later continued as suppressive (prophylactic) therapy. On the third day of hospitalization she passed three small stones that were found to contain calcium oxalate, calcium carbonate, and uric acid. Serum calcium concentration was reportedly normal, but total carbon dioxide and uric acid levels were low (no data given). Serum urea nitrogen and creatinine levels, an intravenous pyelogram, a renal