Autism, Susceptibility To, 16

A number sign (#) is used with this entry because of evidence that susceptibility to autism-16 (AUTS16) is associated with heterozygous mutation in the SLC9A9 gene (608396) on chromosome 3q24. One such family has been reported.

Description

Autism, the prototypic pervasive developmental disorder (PDD), is usually apparent by 3 years of age. It is characterized by a triad of limited or absent verbal communication, a lack of reciprocal social interaction or responsiveness, and restricted, stereotypic, and ritualized patterns of interests and behavior (Bailey et al., 1996; Risch et al., 1999). 'Autism spectrum disorder,' sometimes referred to as ASD, is a broader phenotype encompassing the less severe disorders Asperger syndrome (see ASPG1; 608638) and pervasive developmental disorder, not otherwise specified (PDD-NOS). 'Broad autism phenotype' includes individuals with some symptoms of autism, but who do not meet the full criteria for autism or other disorders. Mental retardation coexists in approximately two-thirds of individuals with ASD, except for Asperger syndrome, in which mental retardation is conspicuously absent (Jones et al., 2008). Genetic studies in autism often include family members with these less stringent diagnoses (Schellenberg et al., 2006).

For a discussion of heterogeneity of autism, see 209850.

Clinical Features

Morrow et al. (2008) identified 2 male sibs with autism disorder and mutation in the SLC9A9 (NHE9) gene in a mutation screening study in patients with autism and epilepsy from nonconsanguineous families. One brother had electroencephalogram-confirmed epilepsy; the other had experienced 2 seizures but did not have known epilepsy at the time of the report. Their mother was reported to have had childhood language delay based on a parental language questionnaire. A patient with autism and epilepsy carrying a deletion juxtaposed to SLC9A9 had previously been identified.

Molecular Genetics

In 2 brothers with autism and seizures and in their mother, Morrow et al. (2008) identified a heterozygous nonsense mutation in the SLC9A9 gene (R423X; 608369.0001). This nonsense change occurs within 2 amino acids of a similar nonsense mutation in SLC9A1 (NHE1; 107310) that causes slow-wave epilepsy in mice, and a similar nonsense mutation in the SLC9A6 (NHE6; 300231) gene that causes an Angelman-like syndrome with both autism and epilepsy (300243). This mutation was not found in over 3,800 control chromosomes.