Objective: The aim of this study was to investigate the genetic causes of autosomal recessive intellectual disabilities (AR-ID) in Hamadan province of Iran.

Materials & Methods: In this descriptive-analytical cross-sectional study, 25 families with more than one affected with putative autosomal recessive intellectual disability were chosen with collaboration of Welfare Organization of Hamadan province. Families were included a total of 60 patients (39 male and 21 female) whose intellectual disability had been confirmed by Raven IQ test. Each family was asked for clinical examination and getting consent form. Blood sample was collected from each family. One proband from each family was tested for CGG repeat expansion in FMR1 gene, chromosomal abnormalities and inborn errors of metabolism. We also performed homozygosity mapping based on STR markers for seven known MCPH loci in families with primary microcephaly and AR-ID.

Results: Five families had full mutation of Fragile X syndrome. No chromosomal abnormalities were identified. Metabolic screening revealed one family with Medium Chain Acyl CoA Dehydrogenase deficiency. None of three families with primary microcephaly and AR-ID showed linkage to any of known seven MCPH loci.

Conclusion: The main causes of ID in Hamadan province were Fragile X syndrome and Autosomal Recessive Primary Microcephaly with the frequencies of 20% and 12%, respectively.