Familial phonological disorders: four pedigrees.

The pedigrees of 4 children with a severe phonological disorder demonstrating three generations of members with speech/language problems are presented. All 4 probands were female with two mothers, two fathers, and five out of six siblings affected. All pedigrees contained family members with dyslexia and learning disabilities as well as speech disorders. Family members varied in the type of speech problems that they demonstrated and the severity of their disorder, thus suggesting variable expressivity and incomplete penetrance. An autosomal dominant mode, a multifactorial-polygenic model, and a sex-specific threshold model for expression are discussed.