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PubMed1988

Segregation analysis of juvenile myoclonic epilepsy.

We examined the inheritance of juvenile myoclonic epilepsy (JME). We looked at both the trait of "epilepsy" and the trait of "epilepsy-plus-EEG abnormalities," since EEG abnormalities are frequently found in the clinically unaffected sibs of JME patients. We tested several modes of inheritance including the fully penetrant recessive and several two-locus models. We could reject all models tested (fully penetrant single-locus and two-locus models) when abnormal EEGs were classified as "unaffected." We could also reject the fully penetrant single locus models when family members with abnormal EEGs were considered "affected." We also rejected the two-locus model where the inheritance at both loci was dominant. The two-locus model where both loci showed recessive inheritance could not be rejected, nor could the model where one locus was dominant and the other recessive. Our results suggest that the underlying predisposition for JME is genetically determined and is partially reflected in the abnormal EEGs found in clinically unaffected family members.

Adult↗
PubMed1989

Modeling the age-of-onset function in segregation analysis: a causal scheme for leprosy.

Several methods have been proposed to take into account the variable age of onset of a disease in genetic analysis. A different approach is presented from an etiological point of view. To illustrate the method, we used leprosy, an infectious disease with a variable age of onset depending on both the time of contamination with the bacillus and the latency of the disease; the role of a major gene in the susceptibility to this disease has been recently detected. The age-of-onset function was modeled to account for the two temporal processes: contamination event and incubation period. For genetic analysis, this function was combined with the probability of being susceptible to the disease, which was expressed by the use of regressive models. To test this new approach, ten sets of 500 nuclear families were simulated considering different hypotheses of contamination risks, which were either constant or dependent on contacts with contagious leprosy patients, and varying the extent to which the disease is heritable. Analyses of these data using two versions of the model indicate that the model can detect familial correlations in variable age of onset and discriminate between the different simulated effects.

Adolescent↗
PubMed1991

Efficient computation of patterned covariance matrix mixed models in quantitative segregation analysis.

The use of patterned covariance matrices in forming pedigree-based mixed models for quantitative traits is discussed. It is suggested that patterned covariance matrix models provide intuitive, theoretically appealing, and flexible genetic modeling devices for pedigree data. It is suggested further that the very great computational burden assumed in the implementation of covariance matrix-dependent mixed models can be overcome through the use of recent architectural breakthroughs in computing machinery. A brief and nontechnical overview of these architectures is offered, as are numerical and timing studies on various aspects of their use in evaluating mixed models. As the kinds of computers discussed in this paper are becoming more prevalent and easier to access and use, it is emphasized that it behooves geneticists to consider their use to combat needless approximation and time constraints necessitated by smaller, scalar computation oriented, machines.

Algorithms↗
PubMed1993

Segregation analysis of body mass index in an unselected French-Canadian sample: the Québec Family Study.

Interest in a single gene etiology for obesity, as assessed by the body mass index (BMI), has been spurred recently by reports of a putative recessive major gene for extreme values, which accounts for as much as 40% of the variance. The major gene hypothesis was evaluated here in the Québec Family Study, a random sample of 375 French-Canadian volunteer families. This report represents one component in a more complete investigation of obesity in these families. In contrast to the recent studies, a major gene hypothesis for BMI was not verified here. Although there was a major effect, it did not conform to a Mendelian pattern of transmission. A multifactorial component (i.e., polygenic and/or common environmental factors) accounted for 42% of the phenotypic variance. In addition, evidence of heterogeneity between the generations was found. The heterogeneity was traced to the major non-Mendelian component (which accounted for 0.01% of the variance in parents and over 40% in offspring) rather than to the multifactorial one. These results would suggest that a simple recessive gene mixed model may not be sufficient to explain the familial distribution of the BMI. Several factors which may have contributed to these results include temporal trends and surrogate effects such as those related to variation in body composition and energy balance components.

Adipose Tissue↗
PubMed1997

Segregation analysis of abdominal visceral fat: the HERITAGE Family Study.

A major gene hypothesis for abdominal visceral fat (AVF) level, both before and after adjustment for total body fat mass, was investigated in 86 white families who participated in the HERITAGE Family Study. In this study, sedentary families were tested for a battery of measures (baseline), endurance exercise trained for 20 weeks, and then remeasured again. The baseline measures reported here are unique in that the variance due to a potentially important environmental factor (activity level) was limited. AVF area was assessed at L4 to L5 by the use of computerized tomography scan, and total body fat mass was assessed with underwater weighing. For fat mass, a putative locus accounted for 64% of the variance, but there was no evidence of a multifactorial component (i.e., no polygenic and/or common familial environmental effects). For AVF area, both a major gene effect accounting for 54% of the variance and a multifactorial component accounting for 17% of the variance were significant. However, after AVF area was adjusted for the effects of total level of body fat, the support for a major gene was reduced. In particular, there was a major effect for fat mass-adjusted AVF area, but it was not transmitted from parents to offspring (i.e., the three transmission probabilities were equal). The importance of this study is twofold. First, these results confirm a previous study that suggested that there is a putative major locus for AVF and for total body fat mass. Second, the findings from the HERITAGE Family Study suggest that the factors underlying AVF area in sedentary families may be similar to those in the population at large, which includes both sedentary and active families. Whether the gene(s) responsible for the high levels of AVF area is the same as that which influences total body fat content remains to be further investigated.

Abdomen↗
PubMed2004

Segregation analysis in cystic fibrosis at-risk family demonstrates that the M348K CFTR mutation is a rare innocuous polymorphism.

OBJECTIVE: Cystic fibrosis (CF; OMIM# 219700) is caused by mutation in the CF transmembrane regulator (CFTR) gene. We investigate whether the (paternal) M348K mutation is a benign polymorphism or a disease-causing mutation in a patient clinically affected with CF, with the second (maternal) CFTR allele identified as N1303K. METHODS: The patient and his father were studied for the presence of mutations in the CFTR gene using the DHPLC system to analyze all CFTR exons. Amplicons showing an abnormal elution profile were sequenced. RESULTS: The CFTR gene from the healthy father has two mutations, M348K and G1244E. The affected son inherited only the G1244E paternal mutation from his father, and hence the two paternal mutations are trans and do not occur in the same CFTR gene. The patient's genotype is G1244E(paternal)/N1303K(maternal). This information was used to study an ongoing pregnancy of the couple, where the fetus inherited the same genotype as the affected proband and therefore is affected. CONCLUSION: M348K in the CFTR gene is not a mutation causing CF, but a rare polymorphism. These data are important for genetic counseling and prenatal diagnosis and illustrate the importance of full sequence data when studying rare mutations.

Alleles↗
PubMed1981

Segregation analysis.

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Dopamine beta-Hydroxylase↗