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Familial developmental dysphasia

Synonym(s) Billard-Toutain-Maheut syndrome
FOXP2-associated dysphasia
Prevalence <1 / 1 000 000
Inheritance Autosomal dominant
Age of onset Childhood
  • F80.1
MeSH -
MedDRA -


Developmental dysphasia is characterized by significant difficulties in acquiring expressive language in children of adequate intelligence in a normal environment without other abnormalities such as intellectual deficit, communication disabilities, deafness, or detectable brain lesions. It affects between 2 and 5% of children who are otherwise unimpaired. Rarer still are severe forms that persist through adulthood, characterized by abnormal expressive language at 6 years (especially phonological impairment and syntax deficit) with a history of no expressive language before 3 years. Several families segregating such disorders have been reported in which males were more commonly affected than females. Studies of these families, as well as other twin studies, indicate a significant role for genetic factors in developmental speech and language disorders. They also suggest that the mode of inheritance is monogenic, probably autosomal dominant. In the case of one exceptional family, comprised of a large three-generation pedigree, approximately half of the members were affected by a severe speech and language disorder, concerning virtually every aspect of grammar and language. In addition, affected members had a severe orofacial dyspraxia, and their speech was largely incomprehensible to the naive listener. The disorder appeared to be transmitted as an autosomal dominant monogenic trait. A genome-wide search for linkage in the family identified a region on chromosome 7 which co-segregated with the speech and language disorder, confirming autosomal dominant inheritance with full penetrance. Further analysis enabled the locus responsible (designated SPCH1) to be localized to a 5.6-cM interval in 7q31. It was shown that the disorder can be caused by mutation in the FOXP2 gene, which may be the first insight into the molecular genetics of the developmental process that culminates in speech and language. Nevertheless this gene is clearly not the only one involved, and epigenetic factors probably also play a role.

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