Genetic factors undoubtedly play a major etiologic role in autism, but how it is inherited remains unanswered. The increased incidence in males suggests possible involvement of the X chromosome.
Using data from 38 multiplex families with autism (2 or more autistic siblings), we performed a multipoint sib-pair linkage analysis between autism and 35 microsatellite markers located on the X chromosome. The model included a single parameter, the risk ratio λXS(ie, ratio of risk to siblings compared with the population prevalence), owing to an X-linked gene. Different λXSvalues were assumed and regions of exclusion were established.
The entire X chromosome could be excluded for a λXS value of 4. The ability to exclude an X-linked gene decreased with smaller λXS values, and some positive evidence was obtained with smaller values. A maximum lod score of 1.24 was obtained at locus DXS424 with a λXS value of 1.5.
We were able to exclude any moderate to strong gene effect causing autism on the X chromosome. Smaller gene effects (λXS<4) could not be excluded, in particular, a gene of small effect located between DXS453 and DXS1001.