Identification of novel loss of function variants in MBOAT7 resulting in intellectual disability

Abstract

The membrane bound O-acyltransferase domain-containing 7 (MBOAT7) gene codes for an enzyme involved in regulating arachidonic acid incorporation in lysophosphatidylinositol. Patients with homozygous nonsense mutations in MBOAT7 have intellectual disability (ID) accompanied with seizure and autism. Accumulating evidences obtained from human genetic studies have shown that MBOAT7 is also involved in fatty liver disease. Here we identified two novel homozygous variants in MBOAT7, NM_024298.5: c.1062C>A; p.(Tyr354*) and c.1135del; p.(Leu379Trpfs*9), in two unrelated Iranian families by means of whole exome sequencing. Sanger sequencing was performed to confirm the identified variants and also to investigate whether they co-segregate with the patients' phenotypes. To understand the functional consequences of these changes, we overexpressed recombinant wild type MBOAT7 and mutants in vitro and showed these mutations resulted in abolished protein synthesis and expression, indicating a complete loss of function. Albeit, we did not trace any liver diseases in our patients, but presence of globus pallidus signal changes in Magnetic Resonance Images might be indicative of metabolic changes as a result of loss of MBOAT7 expression in hepatic cells. These signal changes could also help as an important marker of MBOAT7 deficiency while analyzing the genomic data of patients with similar phenotypes.

Keywords: Hepatic cells; Loss of function; MBOAT7; Whole exome sequencing.