Developmental language disorder - heritability and genetic correlations with other disorders affecting language.

Developmental language disorder (DLD) is a neurodevelopmental disorder primarily affecting language in the absence of a known biomedical condition, which may have a large impact on a person's life and mental health. Family-based studies indicate a strong genetic component in DLD, but genetic studies of DLD are scarce. In this study we estimated the heritability of DLD and its genetic correlations with related disorders and traits in sample of >25,000 individuals from the Danish Blood Donor Study for whom we had both genotype data and questionnaire data on language disorder and language support. We estimated SNP-based heritabilities for DLD and genetic correlations with disorders which may involve spoken language deficits and traits related to spoken language. We found significant heritability estimates for DLD ranging from ∼27 % to ∼52 %, depending on the method used. We found no significant evidence for genetic correlation with the investigated disorders or traits, although the strongest effect was observed for a negative genetic correlation between DLD and nonword repetition ability. To our knowledge, this study reports the first significant heritability estimate for DLD from molecular genetic data.