Autism is a neurodevelopmental disorder that usually arises on the basis of
a complex genetic predisposition. The most significant susceptibility regi
on in the first whole genome screen of multiplex families was on chromosome
7q, although this linkage was evident only in UK IMGSAC families. Subseque
ntly all other genome screens of non-UK families have found some evidence o
f increased allele sharing in an overlapping 40 cM region of 7q. To further
characterize this susceptibility locus, linkage analysis has now been comp
leted on 170 multiplex IMGSAC families. Using a 5 cM marker grid, analysis
of 125 sib pairs meeting stringent inclusion criteria resulted in a multipo
int maximum LOD score (MLS) of 2.15 at F7S477, whereas analysis of all 153
sib pairs generated an MLS of 3.37. The 71 non-UK sib pairs now contribute
to this linkage. Linkage disequilibrium mapping identified two regions of a
ssociation-one lying under the peak of linkage, the other some 27 cM distal
. These results are supported in part by findings in independent German and
American singleton families.