Recent studies of autism spectrum disorder (ASD) and childhood apraxia of speech (CAS) have resulted in conflicting conclusions regarding the comorbidity of these disorders on phenotypic grounds. In a nuclear family with two dually affected and one unaffected offspring, whole-exome sequences were evaluated for single nucleotide and indel variants and CNVs. The affected siblings but not the unaffected sibling share a rare deleterious compound heterozygous mutation in WWOX, implicated both in ASD and motor control. In addition, one of the affected children carries a rare deleterious de novo mutation in the ASD candidate gene RIMS1. The two affected children but not their unaffected sibling inherited deleterious variants with relevance for ASD and/or CAS. WWOX, RIMS1, and several of the genes harboring the inherited variants are expressed in the brain during prenatal and early postnatal development. Results suggest compound heterozygosity as a cause of ASD and CAS, pleiotropic gene effects, and potentially additional, complex genetic effects.
Keywords: Autism spectrum disorder; Childhood apraxia of speech; Comorbidity; Complex trait; Heterogeneity; Language impairment; Multiple hits.