MOLECULAR-GENETIC ANALYSIS OF THE FMR-1 GENE IN A LARGE COLLECTION OFAUTISTIC PATIENTS

A genetic etiology in autism is now strongly supported by family and t win studies. A 3:1 ratio of affected males to females suggests the inv olvement of at least one X-linked locus in the disease, Several report s have indicated an association of the fragile X chromosomal anomaly a t Xq27.3 (FRAXA) with autism, whereas others have not supported this f inding. We have so far collected blood from 105 simplex and 18 multipl ex families and have assessed 141 patients by using the Autism Diagnos tic Interview-Revised (ADI-R), the Autism Diagnostic Observation Scale , and psychometric tests. All four ADI-R algorithm criteria were met b y 131 patients (93%), whereas 10 patients (7%) showed a broader phenot ype of autism. Southern blot analysis was performed with three differe nt enzymes, and filters were hybridized to an FMR-1-specific probe to detect amplification of the CCG repeat at FRAXA. to the complete FMR-1 cDNA probe. and to additional probes from the neighborhood of the gen e. No significant changes were found in 139 patients (99%) from 122 fa milies, other than the normal variations in the population In the case of one multiplex familiy with three children showing no dysmorphic fe atures of the fragile X syndrome (one male meeting 3 out of 4 ADI-algo rithm criteria, one normal male with slight learning disability but ne gative ADI-R testing and one fully autistic female), the FRAXA full-mu tation-specific CCG-repeat expansion in the genotype was not correlate d with the autism phenotype. Further analysis revealed a mosaic patter n of methylation at the FMR-1 gene locus in the two sons of the family , indicating at least a partly functional gene. Therefore, we conclude that the association of autism with fragile X at Xq27.3 is non-existe nt and exclude this location as a candidate gene region for autism.