Genetics: Language disorder gene linked to autism

A girl with autism has a spontaneous deletion in CMIP, a gene associated with specific language impairment (SLI), providing another genetic link between the two disorders. The case study was published 11 June in Autism Research¹.

Autism is characterized by deficits in three core categories, one of which is language impairment. SLI, by contrast, is defined as language impairment alone without other symptoms of developmental disability. Although the two can seem similar in young children, brain imaging studies suggest that the mechanisms underlying autism are distinct from those for SLI.

Still, there is some genetic overlap between the two disorders. In particular, mutations in the CNTNAP2 gene are more common in both individuals with SLI and those with autism than in controls.

In the new study, researchers studied a girl with autism whose parents have no history of neurological disorder or language impairment. She was diagnosed at 3 years of age with autism and developmental delay, and has a history of seizures. At 5, she had a language comprehension level equivalent to that of a 2-and-a-half year old, based on the Reynell Developmental Language Scales.

The girl has a deletion of a 283-kilobase genetic region that disrupts parts of two genes, GAN and CMIP. Lack of GAN leads to a severe neurodevelopmental disorder that is characterized by enlarged neuronal projections. The girl has no sign of this disorder, the researchers say.

The other gene, CMIP, codes for a protein expressed in the brain that plays a role in the cytoskeleton, which gives cells their shape. Various studies have linked variants in CMIP to SLI^2,3 and to reading ability in the general population⁴.  

References:

1: Van der Aa N. et al. Autism Res. Epub ahead of print (2012) PubMed

2: Newbury D.F. et al. Am. J. Hum. Genet. 85, 264-272 (2009) PubMed

3: Newbury D.F. et al. Behav. Genet. 41, 90-104 (2011) PubMed

4: Scerri T.S. et al. Biol. Psychiatry 70, 237-245 (2011) PubMed