[Genetic defects and disorders at the neuromuscular junction]

Area of Science:

• Neuromuscular junction biology
• Molecular genetics
• Neurodegenerative diseases

Context:

• Congenital myasthenic syndromes (CMSs) result from genetic defects in neuromuscular junction (NMJ) proteins.
• These genetic disorders manifest as muscle weakness, fatigability, and amyotrophy, typically presenting in early childhood but sometimes in adulthood.
• The NMJ is a critical synapse between motor neurons and muscle fibers, essential for muscle contraction.

Purpose:

• To review the molecular basis of congenital myasthenic syndromes (CMSs).
• To focus on genetic defects in key NMJ proteins including acetylcholine receptors (AChRs), rapsyn, sodium channel Nav1.4, collagen Q, and choline acetyltransferase.
• To elucidate the pathogenic mechanisms underlying these debilitating neuromuscular disorders.

Summary:

• Genetic mutations in acetylcholine receptor (AChR) subunits, rapsyn, agrin pathway components (LRP4, MuSK, Dok-7), sodium channel Nav1.4, collagen Q, and choline acetyltransferase are identified causes of CMS.
• Defects in these proteins disrupt neurotransmission at the NMJ, leading to characteristic muscle weakness and fatigability.
• While mutations in LRP4 cause syndactyly, AChR, MuSK, and LRP4 are also implicated in autoimmune myasthenia gravis.

Impact:

• Provides a comprehensive overview of the genetic underpinnings of CMS.
• Highlights the critical roles of specific NMJ proteins in maintaining neuromuscular function.
• Informs potential therapeutic strategies targeting NMJ molecular defects for CMS treatment.