Non-coding VMA21 deletions cause X-linked myopathy with excessive autophagy.

Area of Science:

• Genetics and Molecular Biology
• Neuromuscular Disorders
• Cell Biology

Background:

• X-linked Myopathy with Excessive Autophagy (XMEA) is a progressive neuromuscular disorder.
• It is typically caused by VMA21 gene mutations affecting lysosomal proton pump assembly.
• Previous mutations identified were single-nucleotide substitutions impacting VMA21 expression and lysosomal pH.

Observation:

• Two novel VMA21 non-coding microdeletions (one intronic, one 3'UTR) were identified in XMEA patients.
• These mutations represent a new class of genetic alterations leading to XMEA.
• The identified microdeletions resulted in a more severe disease phenotype.

Findings:

• The novel non-coding microdeletions led to earlier onset (neonatal), more diffuse symptoms (including extra-ocular and upper extremity muscles), and faster progression (early ambulation loss).
• These findings indicate that non-coding regions of VMA21 are critical for normal muscle function and disease pathogenesis.
• The severity of XMEA correlates with the extent of VMA21 dysfunction, influenced by the type of mutation.

Implications:

• Genetic testing for XMEA should include screening of non-coding VMA21 regions to ensure comprehensive diagnosis.
• Identifying these new mutation types aids in understanding the full spectrum of XMEA.
• Developing targeted therapies for XMEA, potentially by correcting lysosomal pH, can be advanced by precise genetic diagnosis.