The MTMR9 gene encodes a member of the highly-conserved myotubularin-related protein family. However, unlike other members of this family, the MTMR9 protein does not contain a dual-specificity phosphatase domain. Instead, the protein contains a double-helical motif similar to the SET interaction domain, believed to play a role in the regulation of cell proliferation. MTMR9 has not yet been fully characterized and current knowledge of its function is mainly inferred from studies on its mouse or rat ortholog genes.
In mice, MTMR9 has been found to play a role in the phosphatidylinositol biosynthetic process. Specifically, it binds to MTMR7 and dephosphorylates phosphatidylinositol 3-phosphate and inositol 1,3-bisphosphate. It has also been noted that levels of the Mtmr9 transcript increase in the mouse hypothalamic region after periods of fasting but reduce upon ingestion of a high fat diet.
The MTMR9 gene is located on the short arm of chromosome 8. It spans a length of 43.7 kb of DNA and its coding sequence is spread across 13 exons. The gene encodes a 63.4 kDa protein product composed of 549 amino acids. An additional 53 kDa isoform of the MTMR9 protein exists due to an alternatively spliced transcript variant. While the gene is widely expressed in the human body, overexpression is seen in the uterus, testis and peripheral blood mononuclear cells.
A SNP (rs2293855) in the MTMR9 gene has been found to have a replicated association with obesity in recent case-control association studies.
Monies et al. (2017) illustrated the genomic landscape of Saudi Arabia based on the findings of 1000 diagnostic panels and exomes. One patient, an 11-year-old male, presented with gross motor delay, speech delay, intellectual disability and seizures. He also had 2 sisters that were similarly affected. Whole exome sequencing helped identify a homozygous mutation (c.1415A>T, p.N472I) in exon 9 of the patient’s MTMR gene. This gene mutation was considered a candidate for pathogenicity as it was a novel variant located within the autozygome and was predicted to be deleterious; and the MTMR9 protein has a function in neuronal cells, it forms a complex with MTMR7 and dephosphorylates phosphatidylinositol 3-phosphate and Ins(1,3)P2. The authors noted that further studies are required to confirm this association.
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