Mutation spectrum and clinical features of MYORG in Iranian patients with Primary Familial Brain Calcification (PFBC)

Mutations in myogenesis regulating glycosidase (MYORG), result in autosomal recessive (AR) form of Primary Familial Brain Calcification (PFBC) which is a rare neurodegenerative disease. PFBC is characterized by symmetric brain calcifications, particularly in the thalami, cerebellum, basal ganglia, and subcortical white matter. To date, eight genes have been linked with PFBC, however, currently about half of people with PFBC remain without a genetic diagnosis. Among these genes, MYORG, JAM2, CMPK2, and NAA60 are associated with an AR-PFBC. Within AR-PFBCs, the frequency of mutations in MYORG and JAM2 is 13% and 2%, respectively. In this study, we present a comprehensive clinical and genetic analysis of a group of Iranian PFBC patients.

Clinical and paraclinical assessments of all patients were done. Whole-exome sequencing was performed for all probands. Candidate variants were confirmed and checked in their family members.

Four homozygous variants in MYORG across four families were identified: two novel variants, c.1727G > A;p.Arg576His and c.1687del;p.The563Glnfs*191, in two families and two known mutations, c.176G > A;p.Gly59Asp and c.1092_1097del;p.Phe365_Asp366del in the remaining two families. A potential SNV/CNV in the PFBC-related genes that causes disease was not detected in one proband.

Our study expanded the clinical features and mutation spectrum of MYORG and emphasizes to genetic heterogeneity in different populations. While SLC20A2 mutations are the common cause of PFBC in other populations, MYORG and JAM2 mutations seem to be the main cause of this disease in Iran. This issue could prove to be advantageous in the process of gene prioritization for screening within this specific population.