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POMT1
protein O-mannosyltransferase 1
POMT1 is located on the long (q) arm of chromosome 9, at band 9q34.13. Arm ratio per GRCh38 - banding schematic.
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Overview
POMT1 is located on chromosome 9 and encodes protein O-mannosyltransferase 1, which forms half of a two-part enzyme complex responsible for glycosylation of the alpha-dystroglycan protein. This modification process is particularly important in skeletal muscle tissue and the developing brain, where it supports structural integrity and cellular organisation. Pathogenic changes in POMT1 follow an autosomal recessive inheritance pattern, meaning individuals require variants in both gene copies to develop associated conditions. The gene is clinically significant in the UK, appearing on multiple NHS Genomic Medicine Service panels related to muscular dystrophy, brain malformations, and developmental disorders.
What the gene does
The POMT1 protein partners with POMT2 to form the functional protein O-mannosyltransferase enzyme complex. This complex catalyses the initial step of O-mannosylation, transferring mannose sugar molecules from dolichyl-phosphate-mannose donors onto specific serine and threonine residues of target proteins. The primary substrate is alpha-dystroglycan, a cell-surface glycoprotein that links the internal cytoskeleton to the extracellular matrix surrounding cells. Proper glycosylation of alpha-dystroglycan is essential for its role in stabilising muscle fibres during contraction and protecting them from damage. In the developing brain, glycosylated alpha-dystroglycan guides the migration of neurons to their correct positions, enabling normal formation of brain architecture. The POMT complex shows highest activity in skeletal muscle, foetal brain tissue, and testes, reflecting the tissues most affected when the enzyme is deficient.
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Chromosome location
POMT1 is positioned at chromosomal band 9q34.13 on the long arm of chromosome 9. The gene spans genomic sequence encoding a protein of 747 amino acids. This chromosomal region contains several other genes involved in developmental processes, though POMT1 variants specifically affect the glycosylation pathway critical for dystroglycan function.
Protein structure
The POMT1 protein contains three MIR (mannosyltransferase, IP-3 receptor and ryanodine receptor) domains that are characteristic of mannosyltransferase enzymes. MIR 1 spans amino acids 318 to 381, MIR 2 extends from positions 392 to 449, and MIR 3 occupies residues 453 to 513. These MIR domains are essential for the catalytic activity of the enzyme and enable the protein to recognise and bind its substrate proteins. The arrangement of these domains facilitates the enzyme's ability to work in concert with POMT2, forming the functional heterodimeric complex required for O-mannosylation activity.
Key variants
Pathogenic variants in POMT1 have been identified throughout the gene and generally result in reduced or absent enzyme activity. The severity of associated conditions correlates broadly with the degree of residual enzyme function, though predicting outcomes for individual variants remains challenging. Loss-of-function variants that severely impair the POMT complex typically associate with more severe phenotypes, whilst variants retaining partial activity may result in milder forms of muscular dystrophy.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Variants in POMT1 cause a spectrum of congenital disorders affecting muscle, brain, and eye development, collectively termed dystroglycanopathies. Walker-Warburg syndrome represents the most severe presentation, characterised by profound muscle weakness, structural brain malformations including lissencephaly and cerebellar abnormalities, and eye defects such as retinal dysplasia. Affected individuals with Walker-Warburg syndrome typically face severe developmental challenges and reduced life expectancy. Less severe POMT1-related conditions include muscle-eye-brain disease and limb-girdle muscular dystrophy, where individuals may survive into childhood, adolescence, or adulthood with variable degrees of muscle weakness and intellectual disability.
- Walker-Warburg syndrome Dedicated page coming soon
Inheritance pattern
Conditions caused by pathogenic POMT1 variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
POMT1 holds green (high evidence) status across 16 NHS England gene panels, reflecting strong clinical validity for diagnostic testing. The gene appears on panels including Congenital muscular dystrophy (R79), Intellectual disability (R29), Early onset or syndromic epilepsy (R59), Fetal anomalies (R21), and Malformations of cortical development. Additional memberships include Cerebellar hypoplasia, Congenital disorders of glycosylation, Limb girdle muscular dystrophies (R82), Retinal disorders (R32), and Structural eye disease (R36). This breadth of panel representation reflects the diverse clinical presentations arising from POMT1 variants, spanning neuromuscular, neurological, metabolic, and ophthalmological phenotypes that may prompt genetic investigation through the NHS Genomic Medicine Service.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What inheritance pattern does POMT1 follow?
POMT1-related conditions follow autosomal recessive inheritance, meaning an individual must inherit pathogenic variants in both copies of the gene (one from each parent) to develop a related condition. Carriers with one variant typically remain unaffected.
Why does POMT1 affect both muscle and brain tissue?
The POMT1 enzyme modifies alpha-dystroglycan, a protein essential in both skeletal muscle (where it stabilises muscle fibres) and the developing brain (where it guides neuron migration). Deficiency in this modification process disrupts normal function in both tissue types.
Are all POMT1 variants equally severe?
No, the severity of POMT1-related conditions varies considerably depending on how much the variant affects enzyme function. Variants causing complete loss of activity typically result in Walker-Warburg syndrome, whilst those preserving partial function may lead to milder muscular dystrophy phenotypes.