Behavior Genetics, VoL 23, No. 3, 1993 Segregation Analysis of Speech and Language Disorders Barbara A. Lewis, 1,3 Nancy J. Cox, 2 and Pamela J. Byard 1 Received 6 April 1992--Final 3 Nov. 1992 Complex segregation analysis was performed on pedigrees ascertained through 45 pro- bands (26 males, 19 females) with a history of preschool speech and language disorders. Hypotheses concerning mode of inheritance were tested using the POINTER segregation analysis program. Although there is strong evidence for familial transmission of this trait, we were unable to distinguish between a major gene and multifactorial transmission model using likelihood-ratio chi-square tests. Future studies with quantitative measures of speech and language disorders are needed to resolve the issue of mode of inheritance for this trait. KEY WORDS: Speech disorders; language disorders; segregation analysis; developmental dis- orders; learning disabilities. INTRODUCTION Recent evidence suggests a familial basis to some developmental speech and language disorders pre- viously of unknown etiology (Lewis, 1987, 1989, 1990; Tallal et al., 1989, 1991; Tomblin, 1989). These studies have reported an increased incidence of speech and language disorders, dyslexia, and other learning problems among family members of pro- bands with speech and language disorders com- pared to family members of probands with normally developing speech and language skills. Reports have estimated 70% of children with language impair- ments to have positive family histories for speech, language, or learning impairments (Tallal et aL, 1991). Studies examining incidences of disorders among first-degree relatives of the probands, have reported brothers most often affected (up to 41.5%) (Lewis, 1987, 1991; Tallal el al., 1989; Tomblin, 1989). Reports of parental affection status have been inconclusive, with some researchers reporting an Department of Pediatrics, Case Western Reserve University School of Medicine, Rainbow Babies and Childrens Hospital, Cleveland, Ohio 44106. -" Department of Medicine, University of Chicago, Chicago, lllinois. 3 To whom correspondence should be addressed at Department of Pediatrics, Rainbow Babies and Childrens Hospital, 2101 Adelbert Road, Cleveland, Ohio 44106. 291 increased incidence among fathers compared to mothers (Neils and Aram, 1986; Tallal et al., 1989) and others reporting mothers as often affected as fathers (Lewis, 1987, 1990; Tomblin, 1989). This discrepancy may be the result of differing criteria for determining affection status. Tatlal et aL (1989) considered an individual affected if he o1: she re- ported any speech, language, or learning difficulty, whereas Lewis et al. (1989) classified an individual as affected only if he or she reported speech and language problems. Overall percentages of affected first-degree relatives range from 22.9 to 41.5%. Again, differences may be explained by restrictive versus broad criteria for determining affection status. Reports of single kindreds (Arnold, 1961; Eu- tis, 1947; Gopnik, 1990; Hurst et al., 1990; Lewis, 1990; Saleeby et al., 1978; Samples and Lane, 1985) are remarkable because of the large number of af- fected family members and the severity of the dis- orders. Often, in these families the disorder appears to be inherited in an autosomal dominant fashion with variable expressivity and incomplete penetr- ance. However, these families are not representa- tive of the majority of individuals with speech and language disorders as the disorder is not as perva- sive or severe in most families of probands with speech and language disorders. Few- studies have examined multiple pedigrees 0001-8244/93/0500-0291507.00/0 9 1993 Plenum Publishing Corporation