Recovery and persistence of stuttering among relatives of stutterers.

Recovery and persistence of stuttering were examined in the first-degree relatives of a large group of adult persistent stutters. The percentage of recovered individuals reported in these families supports the hypothesis that recovered and persistent stuttering are not independent disorders. Sex and type of relative were significant variables in the distributions of recovery and persistence of stuttering. Handedness in male subjects and birth order did not distinguish between recovered and persistent stutterers. Female recovered stutterers had significantly earlier ages of stuttering onset than the other groups (male recovered stutterers and male and female persistent stutterers). Female recovered stutterers also tended to recover earlier than male recovered stutterers, and the durations of stuttering symptoms were similar in both sexes.

Language onset and concomitant speech and language problems in subgroups of stutterers and their siblings.

Time of language onset and frequencies of speech and language problems were examined in stutterers and their nonstuttering siblings. These families were grouped according to six characteristics of the index stutterer: sex, recovery or persistence of stuttering, and positive or negative family history of stuttering. Stutterers and their nonstuttering same-sex siblings were found to be distributed identically in early, average, and late categories of language onset. Comparisons of six subgroups of stutterers and their respective nonstuttering siblings showed no significant differences in the number of their reported articulation problems. Stutterers who were reported to be late talkers did not differ from their nonstuttering siblings in the frequency of their articulation problems, but these two groups had significantly higher frequencies of articulation problems than did stutterers who were early or average talkers and their siblings.

An easy-to-use maximum-likelihood method of estimating the ascertainment probability.

An easy-to-compute statistic for estimating the ascertainment probability is proposed. This statistic is determined through the use of the maximum-likelihood principle and, therefore, in addition to being easy to compute, has the desirable properties of a maximum-likelihood statistic. Variance tables are given to facilitate computation of the estimate and its variance.

Analysis of the sibship patterns of stutterers.

Analyses of birth rank, age separation, and the frequency of stutterers in birth ranks before and after the proband were undertaken for the purpose of verifying or disproving conjectures made by other authors on possible relationships between family structures and stuttering. Results based on data drawn from over 300 sibships, showed (a) stutterers were randomly distributed among the birth ranks, (b) the age separation of the siblings was independent of stuttering status, and (c) the frequency of stutterers in birth ranks before the proband and the frequency of stutterers in birth ranks after the proband were not significantly different.

Penetrance estimates and recurrence risks for fibromuscular dysplasia.

The mode of transmission, penetrance, birth order and sex bias effects are analyzed for fibromuscular dysplasia data. These analyses were done to facilitate genetic counseling for this disease.

Estimating sex ratio biases in X-linked disorders: is there an excess of males in families with X-linked ichthyosis?

We derive the conditional probabilities for estimating the sex ratio in families ascertained through affected males for the study of X-linked recessive diseases. These conditional probabilities correct for the fact that the probability that a family will be ascertained increases with the number of males in the family. Data from four published studies for X-linked ichthyosis vulgaris are analyzed, three having an excess of males and one having a highly statistically significant excess of males. It is not known if this difference in the two samples represents a biological difference between the two populations or an unrecognized ascertainment bias.

Counseling for dominant traits: a correction for the ascertainment bias due to referral for analysis.

Genetic heterogeneity complicates genetic counseling because the correct mode of inheritance must be determined independently for each pedigree. When autosomal and X-linked dominants inheritance mechanisms are known, as for example with retinitis pigmentosa, then only families where male-to-male transmission is observed may be readily counseled. The other pedigrees may be autosomal but lack male-to-male transmission due to chance segregation. Since only the pedigrees without male-to-male transmission are analyzed for their mode of inheritance, there is an ascertainment bias which must be corrected when evaluating the likelihood of the two inheritance patterns. A method to correct for this bias using conditional likelihoods is given, along with examples to demonstrate its use.

A statistical analysis of birth-order effects with application to data on pyloric stenosis.

A method is presented for correcting incomplete data for birth-order analysis and variations in the ascertained incidence of affected individuals are allowed. The statistical analysis involves application of a test developed by Wilcoxon, Mann and Whitney, and Haldane and Smith. Examples are detailed for data correction, and the analysis of data for pyloric stenosis is discussed.

Effects of reproductive compensation and genetic drift on X-linked lethals.

A revival of interest in Haldane's equilibrium theory for X-linked lethals has been stimulated by the introduction of accurate tests for the detection of female heterozygotes in Lesch-Nyhan disease. Application of these tests appears to indicate an excess of familial cases. This excess can be attributed to ascertainment bias, a difference in female and male mutation rates, genetic drift, and reproductive compensation. Reproductive compensation will be particularly effective in increasing the proportion of familial cases if (1) birth control is widespread; (2) selection against affected males acts in utero; (3) affected sons show symptoms at an early age; and (4) sons are more highly valued than daughters. We demonstrate how only a few generations of reproductive compensation are sufficient to achieve an approximate equilibrium between selection and mutation showing a high proportion of familial cases. We also discuss the random fluctuations around equilibrium caused by genetic drift.

A goodness-of-fit test for the polygenic threshold model: application to pyloric stenosis.

A new test of goodness of fit for the polygenic threshold model is proposed. This test, when applied to disorders showing different incidence rates in males and females, is designed to account for ascertainment in more detail than previously done by other investigators. This is accomplished by computing the expected distribution of nuclear families with more than one affected sib conditioned on several family-dependent variables, including whether each family was ascertained via only affected boys or via at least one affected girl. A direct measure of the probability of observing a data set is thereby derived. The test, when applied to data on pyloric stenosis, exposes the critical nature of the ascertainment procedures. Different levels of statistical significance are obtained when mode of ascertainment is taken into account than when the mode of ascertainment is ignored.