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Assortative mating models: Problems and possibilities
ABSTRACTS OF ANNUAL MEETING
19x0
17 I
in consultation within the 2 hospitals. Of those referred from outside 31.6:,<, came from general practitioners, 27",, from specialists and 7.5"" from other agencies; obstetricians accounted for 40:,, of referrals. The aetiology of the affected person was chromosomal in 37",:; due to a neural tube defect in l4:<,, li3;;, had single major defects, multiple defects and syndromes; a further I3"7 were neurological while haematological and skeletal conditions accountcd hi3% each. Apart from the chromosomal disorders inheritance was Mendelian in 25",,, multifactoi-ial in 23";). and I .6% came to discuss some degree of consanguinity. KINDREDS AND PATERNITY AS DEPICTED BY ABORIGINAL ROCK ART
JOHN WARWICK COX Muter Mrsericordirie Childrcw 'k Hos~iital,Sorrtli Brishrinc Rock art from the Pilbara region of north-west Australia does not have the stiffness and crudity ofdrawings i i ~ i i i d in south-eastern Australia. Instead, figures display inovemeiit and excitation as they hunt, dance. inakc Iovc and fight. Some appear to represent fmiily groups, with linkage lines not unlike a geneticist's kindred. The female is distinguished by genitalia and smaller overall size. Often a linejoins the genitalia oi'malc and fcmale figures representing semen transference, or family groups. lsolaled feinale figures with a genital discharge Iiiic or dots, linking to smaller asexual figures between her legs is suggestive of' umbilical cords a n d children. A recently identified example of rock art has features differentiating it from pi-cviously known examples. There are 2 figures. The central figure is presumably a fully initiated male a s it is the larger. has a headdress ; i d tribal markings. It is joined by a broad line to the penis of the smaller male. This rock art 5uggests that knowledge of paternity may have been known to the Aborigines, contrary to knowledge of other hunter-gatherer peoples. Further understanding of the Aborigine's concept of family linkage must help to integrate hiin a s ii respected member of Australian society yet enable him to maintain his ethnic respect. MONITORING CONGENITAL MALFORMATIONS
PAUL LANCASTER Univc~rsityof Svdnnej,
Nalronul Perinatol Stativtic.s Unit, Coninior7i~~c'ulth lii.stitn/c~[ J / Ifc~trlth.
The limitations of data about the incidence of major congenital inalformations in Australia are well rccognizcd. Existing or planned perinatal data collections throughout Australia will soon provide information about malformations for all births. This information will be included on a notification of birth form with other demographic a n d medical vnriables for the mother and the baby. Perinatal death certificates will be used as the other source of data about malformations. Each State and Territory health authority will have the responsibility for the collection and collation of data from these primary sources. Uniform data collection methods arc essential so that valid comparisons can be made. Subsequent coding, data processing and analysis will be done by thc National I'crinatal Statistics Unit. Trends in Australia will be compared with other countries by participation in the International Clearinghouse for Birth Defects Monitoring Systems. Additional data sources such as cytogenetic laboratories, specialty clinics and hospital admissions can be uscd to supplement the information from notification of birth forms and death certificates f o r more specilic studies. Genetic applications of these data include the development of regional malformation registerh, the evaluation 01' antenatal diagnosis and the evaluation of genetic counselling services. ASSORTATIVE MATING MODELS: PROBLEMS AND POSSIBILITIES
SUSAN R. WILSON University
Department qf Statistics, In.crituie o/ A d w m c ~ dSlurlic,.s. Austdrrm Nrrtionrrl
In population genetics many models of assortative mating for a single characteristic have becii proposed. Such models usually involve just a single locus. Few models for a continuous trait involving more than one locus have been considered. The most commonly used model, and that underlying the usual analysis of correlations between relatives to obtain heritability estimates, is Fisher's classical model. However, it can be shown that i f one considers this multilocus model using a similar approach to that for a single locus model then anomalies occur. One method of overcoming the difficulties is to postulate a socio-economic variable (based on an individual's lifetime experiences) with respect to which individuals are mating assortatively. There is assumed to be a relationship between this socio-economic variable and the characteristic being studied. As well. individuals may be mating assortatively for the characteristic under consideration.
I72
Pathology (1981). 13, January
H U M A N GENETICS SOCltTY Ok AUSTKALASIA
Data to resolve many issue> that arise l'rom assortative mating models of a continuouh characteristic are sparst.. The above indicates that data on characteristics associated with an individual's lifetime experiences that affect his choice of partner and that are also associated with the trait under consideration may :ilso need to be collected PERSISTENT ELEVATION OF AMNIOTIC FLUID ALPHA-FETOPROTEIN WITH A NORMAL FETUS
A. E. CLAGUE. A. E. BARR.T. B. LYNCH*,D. B ~ J N T I N&E D. J . MORRIS PUfh~J/OgJ &,/JUrtnil'iir, /?oj.ir/ Btishunc, Ho.vpitrr/, *Priwrte Putho/ogist, Roc,khuniplorr Amniocentesis was performed at 13 weeks gestation on a woman with a history of one child with multiple dcl'ormitics. The lluid was brown-green uith n o red cells. It had an elevated alpha letoprotein (AFP) level of 4x0 mgll. but ii normal acetylcholinesterase level ol9.4 U:l. Two subsequent amniocenteses at 16 and 19 wk had a similar appearance and A F P levels of290 and 120 mgll respectively. Aeetylcholinesterase was normal in each case. Therapeutic abortion was done but examination of the foetus revealed no open neural tube defect, exomphalos, renal disease. or alimentary tract atresia. The placenta showed a considerable area of old infarction of the decidual bcd and ii local area of placental sclerosis consistent with partial placental separation.
SCREENING FOR HYPOTHYROIDISM: AGE OF SAMPLE AND CHANCE OF ITS FALLING BELOW THE CUT-OFF POINT
BRIDGET W ILCKEN O l i w r Lailium LuhorutorI,. Hrulih Con7riiis,cioi1 ol Ncw Sourli Wul12.v The 3 hi-gcst hypothyroid scr-cening programmes in Australia use a thyroxine (T,) assay on dried blood spots its the primary w c c n , backed up by a thyrotrqpin (TSH) measurement on samples whose T, value falls into the lowest IO",, 01' a n y batch. I t was recently shown that recoverable T, declines upon storage of blood spots at high temperatures or in direct sunlight. In N S.W. we have recorded the age, from collection to receipt in the laboratory. ofsamples. and thc age ofthoac samples lidling into the lowest lo":, ofeach batch. Twenty-five percent of samples arrived within 1-2 d ofcollection, but only I .6",,of thew fell into the lowest lo",, of the batch in which they were wmpled. By contrast almost IO",, of \;tmples arrived more than 10 d d t e r collection, and 27",, of these fell into the lowest l07,>of the batch. The range 0 1 results (or one week is shown in the table. Age of sample (days)
1-2
3 4
5-6
7-5
9 0
10
Per cent of total ( n = 1501) Per cent below cut-off
25 1.6
26 8
19
17 16
7 18
27
12
10
Of27 detected cascs of hypothyroidism, only 2 Cell into the group whose sample arrived in I 4 d. We concluded that dclny i n remitting samples to the laboratory seriously distorts results and may lead to missed Cases oi' hypothyroidism particularly in those samples submitted promptly, i n programmes with a primary T, screeti. PRENATAL DIAGNOSIS-AMNIOTIC
FLUID CHROMOSOME STUDIES IN 1000 CASES
J . A. BELL, B. H. WILSOK& A. J . AYSFOKD Cytogmetics Sr~c,tion,S t u f i , Hcultli Liihorriror~, Bri.\huncj Over ii 6-yr period (1974 80) 1000 samples of amniotic fluid were referred for chromosome analysis. Five hundred and thirty-six patients (53.6",,)were referred because of advanced maternal age, 105 (10.5%) because o l t h e birth o f a previous child with Down's syndrome or a family history of Down's syndrome, 7 (0.72;) were translocation carriers and 17 ( I 7",,) had a previous child with a chromosome abnormality other than Down's syndrome. The husbands o f 3 patients had chromosome abnormalities and there were 3 referrals from families with sex linked disorders. Thirtythree per cent o f t h e sample (329 cases) comprised a miscellaneous group including those referred primarily for xlcto protein estimation and maternal anxiety. Sixteen major chromosome abnormalities were detected and o f these, 12 pregnancies were terminated, one pregnancy miscarried, one resulted in ii stillbirth and 2 continued to term. Foetal loss occurred in 19 pregnancies (1.9":;). Twenty-six specimens failed to grow (2.6",,) but I0 of these were considered unsuitable for culture on arrival at the laboratory.
19x0
17 I
in consultation within the 2 hospitals. Of those referred from outside 31.6:,<, came from general practitioners, 27",, from specialists and 7.5"" from other agencies; obstetricians accounted for 40:,, of referrals. The aetiology of the affected person was chromosomal in 37",:; due to a neural tube defect in l4:<,, li3;;, had single major defects, multiple defects and syndromes; a further I3"7 were neurological while haematological and skeletal conditions accountcd hi3% each. Apart from the chromosomal disorders inheritance was Mendelian in 25",,, multifactoi-ial in 23";). and I .6% came to discuss some degree of consanguinity. KINDREDS AND PATERNITY AS DEPICTED BY ABORIGINAL ROCK ART
JOHN WARWICK COX Muter Mrsericordirie Childrcw 'k Hos~iital,Sorrtli Brishrinc Rock art from the Pilbara region of north-west Australia does not have the stiffness and crudity ofdrawings i i ~ i i i d in south-eastern Australia. Instead, figures display inovemeiit and excitation as they hunt, dance. inakc Iovc and fight. Some appear to represent fmiily groups, with linkage lines not unlike a geneticist's kindred. The female is distinguished by genitalia and smaller overall size. Often a linejoins the genitalia oi'malc and fcmale figures representing semen transference, or family groups. lsolaled feinale figures with a genital discharge Iiiic or dots, linking to smaller asexual figures between her legs is suggestive of' umbilical cords a n d children. A recently identified example of rock art has features differentiating it from pi-cviously known examples. There are 2 figures. The central figure is presumably a fully initiated male a s it is the larger. has a headdress ; i d tribal markings. It is joined by a broad line to the penis of the smaller male. This rock art 5uggests that knowledge of paternity may have been known to the Aborigines, contrary to knowledge of other hunter-gatherer peoples. Further understanding of the Aborigine's concept of family linkage must help to integrate hiin a s ii respected member of Australian society yet enable him to maintain his ethnic respect. MONITORING CONGENITAL MALFORMATIONS
PAUL LANCASTER Univc~rsityof Svdnnej,
Nalronul Perinatol Stativtic.s Unit, Coninior7i~~c'ulth lii.stitn/c~[ J / Ifc~trlth.
The limitations of data about the incidence of major congenital inalformations in Australia are well rccognizcd. Existing or planned perinatal data collections throughout Australia will soon provide information about malformations for all births. This information will be included on a notification of birth form with other demographic a n d medical vnriables for the mother and the baby. Perinatal death certificates will be used as the other source of data about malformations. Each State and Territory health authority will have the responsibility for the collection and collation of data from these primary sources. Uniform data collection methods arc essential so that valid comparisons can be made. Subsequent coding, data processing and analysis will be done by thc National I'crinatal Statistics Unit. Trends in Australia will be compared with other countries by participation in the International Clearinghouse for Birth Defects Monitoring Systems. Additional data sources such as cytogenetic laboratories, specialty clinics and hospital admissions can be uscd to supplement the information from notification of birth forms and death certificates f o r more specilic studies. Genetic applications of these data include the development of regional malformation registerh, the evaluation 01' antenatal diagnosis and the evaluation of genetic counselling services. ASSORTATIVE MATING MODELS: PROBLEMS AND POSSIBILITIES
SUSAN R. WILSON University
Department qf Statistics, In.crituie o/ A d w m c ~ dSlurlic,.s. Austdrrm Nrrtionrrl
In population genetics many models of assortative mating for a single characteristic have becii proposed. Such models usually involve just a single locus. Few models for a continuous trait involving more than one locus have been considered. The most commonly used model, and that underlying the usual analysis of correlations between relatives to obtain heritability estimates, is Fisher's classical model. However, it can be shown that i f one considers this multilocus model using a similar approach to that for a single locus model then anomalies occur. One method of overcoming the difficulties is to postulate a socio-economic variable (based on an individual's lifetime experiences) with respect to which individuals are mating assortatively. There is assumed to be a relationship between this socio-economic variable and the characteristic being studied. As well. individuals may be mating assortatively for the characteristic under consideration.
I72
Pathology (1981). 13, January
H U M A N GENETICS SOCltTY Ok AUSTKALASIA
Data to resolve many issue> that arise l'rom assortative mating models of a continuouh characteristic are sparst.. The above indicates that data on characteristics associated with an individual's lifetime experiences that affect his choice of partner and that are also associated with the trait under consideration may :ilso need to be collected PERSISTENT ELEVATION OF AMNIOTIC FLUID ALPHA-FETOPROTEIN WITH A NORMAL FETUS
A. E. CLAGUE. A. E. BARR.T. B. LYNCH*,D. B ~ J N T I N&E D. J . MORRIS PUfh~J/OgJ &,/JUrtnil'iir, /?oj.ir/ Btishunc, Ho.vpitrr/, *Priwrte Putho/ogist, Roc,khuniplorr Amniocentesis was performed at 13 weeks gestation on a woman with a history of one child with multiple dcl'ormitics. The lluid was brown-green uith n o red cells. It had an elevated alpha letoprotein (AFP) level of 4x0 mgll. but ii normal acetylcholinesterase level ol9.4 U:l. Two subsequent amniocenteses at 16 and 19 wk had a similar appearance and A F P levels of290 and 120 mgll respectively. Aeetylcholinesterase was normal in each case. Therapeutic abortion was done but examination of the foetus revealed no open neural tube defect, exomphalos, renal disease. or alimentary tract atresia. The placenta showed a considerable area of old infarction of the decidual bcd and ii local area of placental sclerosis consistent with partial placental separation.
SCREENING FOR HYPOTHYROIDISM: AGE OF SAMPLE AND CHANCE OF ITS FALLING BELOW THE CUT-OFF POINT
BRIDGET W ILCKEN O l i w r Lailium LuhorutorI,. Hrulih Con7riiis,cioi1 ol Ncw Sourli Wul12.v The 3 hi-gcst hypothyroid scr-cening programmes in Australia use a thyroxine (T,) assay on dried blood spots its the primary w c c n , backed up by a thyrotrqpin (TSH) measurement on samples whose T, value falls into the lowest IO",, 01' a n y batch. I t was recently shown that recoverable T, declines upon storage of blood spots at high temperatures or in direct sunlight. In N S.W. we have recorded the age, from collection to receipt in the laboratory. ofsamples. and thc age ofthoac samples lidling into the lowest lo":, ofeach batch. Twenty-five percent of samples arrived within 1-2 d ofcollection, but only I .6",,of thew fell into the lowest lo",, of the batch in which they were wmpled. By contrast almost IO",, of \;tmples arrived more than 10 d d t e r collection, and 27",, of these fell into the lowest l07,>of the batch. The range 0 1 results (or one week is shown in the table. Age of sample (days)
1-2
3 4
5-6
7-5
9 0
10
Per cent of total ( n = 1501) Per cent below cut-off
25 1.6
26 8
19
17 16
7 18
27
12
10
Of27 detected cascs of hypothyroidism, only 2 Cell into the group whose sample arrived in I 4 d. We concluded that dclny i n remitting samples to the laboratory seriously distorts results and may lead to missed Cases oi' hypothyroidism particularly in those samples submitted promptly, i n programmes with a primary T, screeti. PRENATAL DIAGNOSIS-AMNIOTIC
FLUID CHROMOSOME STUDIES IN 1000 CASES
J . A. BELL, B. H. WILSOK& A. J . AYSFOKD Cytogmetics Sr~c,tion,S t u f i , Hcultli Liihorriror~, Bri.\huncj Over ii 6-yr period (1974 80) 1000 samples of amniotic fluid were referred for chromosome analysis. Five hundred and thirty-six patients (53.6",,)were referred because of advanced maternal age, 105 (10.5%) because o l t h e birth o f a previous child with Down's syndrome or a family history of Down's syndrome, 7 (0.72;) were translocation carriers and 17 ( I 7",,) had a previous child with a chromosome abnormality other than Down's syndrome. The husbands o f 3 patients had chromosome abnormalities and there were 3 referrals from families with sex linked disorders. Thirtythree per cent o f t h e sample (329 cases) comprised a miscellaneous group including those referred primarily for xlcto protein estimation and maternal anxiety. Sixteen major chromosome abnormalities were detected and o f these, 12 pregnancies were terminated, one pregnancy miscarried, one resulted in ii stillbirth and 2 continued to term. Foetal loss occurred in 19 pregnancies (1.9":;). Twenty-six specimens failed to grow (2.6",,) but I0 of these were considered unsuitable for culture on arrival at the laboratory.