MAN1B1 Mutation Leads to a Recognizable Phenotype: A Case Report and Future Prospects.

Intellectual disability (ID) is one of the most common reasons for referral to genetic counseling. Nevertheless, in over 50% of the cases no diagnosis can be made. Here, we present how exome sequencing in combination with medical genetics evaluation led to the identification of a known pathogenic homozygous mutation in MAN1B1 in a consanguineous Turkish family. The phenotype comprised mild ID, truncal obesity and facial dysmorphism, comparable to that of the patients in the 3 recent publications on mutations in this gene. Clinically, the majority of patients in the literature showed congenital disorder of glycosylation syndrome type 2. In this study, we summarize the current knowledge about MAN1B1 mutations from the literature as well as databases and suggest that exome sequencing should be implemented in a larger scale in routine diagnostics, since autosomal recessive ID has proven to be extremely heterogeneous. Even syndromic patterns may only become recognizable retrospectively.