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At least 487 records · Page 27Linked to original sources
PubMed1978

Efficiency and robustness of pedigree segregation analysis.

Different pedigree structures and likelihoods are examined to determine their efficiency for parameter estimation under one-locus models. For the cases simulated, family size has little effect; estimates based on unconditional likelihoods are generally more efficient than those based on conditional likelihoods. The proposed method of pedigree analysis under a one-locus model is found to be robust in the analysis of nuclear families: skewness of the data and polygenic inheritance will not lead to the spurious detection of major loci unless they occur simultaneously, and together with a moderate amount of environmental correlation among sibs.

Gene Frequency↗
PubMed1994

Multiple etiologies for Alzheimer disease are revealed by segregation analysis.

We have evaluated several transmission models for Alzheimer disease (AD), using the logistic regressive approach in 401 nuclear families of consecutively ascertained and rigorously diagnosed probands. Models postulating no major gene effect, random environmental transmission, recessive inheritance, and sporadic occurrence were rejected under varied assumptions regarding the associations among sex, age, and major gene susceptibility. Transmission of the disorder was not fully explained by a single Mendelian model for all families. Stratification of families as early- and late-onset by using the median of family mean onset ages showed that, regardless of the model studied, two groups of families fit better than a single group. AD in early-onset families is transmitted as an autosomal dominant trait with full penetrance in both sexes and has a gene frequency of 1.5%. Dominant inheritance also gave the best fit of the data in late-onset families, but this hypothesis was rejected, suggesting the presence of heterogeneity within this subset. Our study also revealed that genetically nonsusceptible males and females develop AD, indicating the presence of phenocopies within early-onset and late-onset groups. Moreover, our results suggest that the higher risk to females is not solely due to their increased longevity.

Age of Onset↗
PubMed1994

Segregation analysis of complex phenotypes: an application to schizophrenia and auditory P300 latency.

Traditional models of the genetic transmission of human diseases have often assumed that the phenotype is a simple dichotomous trait, which is unrealistic for many psychiatric conditions, and may result in loss of valuable information. We describe a new model for complex phenotypes, implemented in the program COMDS, which subclassifies normal and affected individuals into polychotomies correlated with the underlying genetic liability to the disorder. The model is applied to 18 Scottish pedigrees ascertained for schizophrenia, in which auditory P300 latency had been measured as a possible correlate of the genetic predisposition to schizophrenia. The results suggest that there may be a major locus for schizophrenia, but that there are also other familial determinants, possibly a second modifier locus. In addition, the results indicate that auditory P300 latency may be a useful measure of the genetic predisposition to schizophrenia among asymptomatic relatives, although the relationship between P300 latency and the degree of genetic predisposition in clinical cases was not significant, presumably because other factors are operating on P300 latency. Because of the possible selection biases in this sample, there is a need to replicate these findings in systematically ascertained pedigrees.

Discriminant Analysis↗
PubMed1993

Segregation analysis in a man heterozygous for a pericentric inversion of chromosome 7 (p13;q36) by sperm chromosome studies.

We have analyzed 140 sperm chromosome complements from a subfertile man heterozygous for an inv(7)(p13;q36). Seventy-five percent of the chromosome complements were not recombinant: 37.9% contained the normal chromosome 7, and 37.1% contained the inverted chromosome 7. Twenty-five percent of the 140 were recombinant: 7.1% carried a recombinant chromosome 7 with a duplication p and deletion q, 17.1% carried a recombinant chromosome 7 with a duplication q and deletion p, and 0.7% carried both recombinant chromosomes. The frequency of structural chromosomal aberrations unrelated to the inversion was 11.4%, and the frequency of aneuploidy was 2.9%. Both frequencies were not significantly different from those in control donors. Two sperm complements with a second independent, contiguous inversion involving one of the original breakpoints (q36) were observed (1.4%). The risk of producing chromosomally abnormal offspring or spontaneous abortions would be 34.3%. The proportion of X-bearing and Y-bearing sperm was 46.8% and 53.2%, respectively, not significantly different from the expected 1:1 ratio.

Adult↗
PubMed1985

Segregation analysis of hemophilia A and B.

We analyzed a sample of 1,485 families with hemophilia A and B and with unknown diagnosis. The frequency of sporadic cases was estimated to be .166 and .078 for the two types of hemophilia, respectively. The sex ratio of mutation rates did not differ significantly from unity. The average age of maternal grandfathers of probands at birth of mothers with a single child, affected by hemophilia B, and of maternal grandfathers of probands at birth of mothers with more than one child affected by hemophilia B, was higher than the age in appropriate control groups.

Age Factors↗