Mutations in the alpha 1,2-mannosidase gene, MAN1B1, cause autosomal-recessive intellectual disability.
Rafiq M.A., Kuss A.W., Puettmann L., Noor A., Ramiah A., Ali G., Hu H., Kerio N.A., Xiang Y., Garshasbi M., Khan M.A., Ishak G.E., Weksberg R., Ullmann R., Tzschach A., Kahrizi K., Mahmood K., Naeem F., Ayub M., Moremen K.W., Vincent J.B., Ropers H.H., Ansar M., Najmabadi H.
We have used genome-wide genotyping to identify an overlapping homozygosity-by-descent locus on chromosome 9q34.3 (MRT15) in four consanguineous families affected by nonsyndromic autosomal-recessive intellectual disability (NS-ARID) and one in which the patients show additional clinical features. Four of the families are from Pakistan, and one is from Iran. Using a combination of next-generation sequencing and Sanger sequencing, we have identified mutations in the gene MAN1B1, encoding a mannosyl oligosaccharide, alpha 1,2-mannosidase. In one Pakistani family, MR43, a homozygous nonsense mutation (RefSeq number NM_016219.3: c.1418G>A [p.Trp473*]), segregated with intellectual disability and additional dysmorphic features. We also identified the missense mutation c. 1189G>A (p.Glu397Lys; RefSeq number NM_016219.3), which segregates with NS-ARID in three families who come from the same village and probably have shared inheritance. In the Iranian family, the missense mutation c.1000C>T (p.Arg334Cys; RefSeq number NM_016219.3) also segregates with NS-ARID. Both missense mutations are at amino acid residues that are conserved across the animal kingdom, and they either reduce k(cat) by ∼1300-fold or disrupt stable protein expression in mammalian cells. MAN1B1 is one of the few NS-ARID genes with an elevated mutation frequency in patients with NS-ARID from different populations.