A Compound Heterozygous Mutation in Calpain 1 Identifies a New Genetic Cause for Spinal Muscular Atrophy Type 4...

Area of Science:

• Neurology
• Genetics
• Molecular Biology

Background:

• Spinal Muscular Atrophy (SMA) is a neuromuscular disease affecting motor neurons.
• The genetic basis for Spinal Muscular Atrophy type 4 (SMA4), an adult-onset form, remains largely unknown.
• Current understanding of SMA genetics primarily involves mutations in the survival motor neuron 1 (SMN1) gene.

Purpose of the Study:

• To investigate the genetic and pathogenic causes of Spinal Muscular Atrophy type 4 (SMA4).
• To identify novel genes associated with the SMA4 phenotype.
• To characterize the functional consequences of identified mutations in patient-derived cells.

Main Methods:

• Whole exome sequencing was performed on siblings diagnosed with SMA4.
• Genetic mutations were identified in the calpain-1 (CAPN1) gene.
• Skin fibroblasts from patients were analyzed for CAPN1 protein levels, protease activity, and SMN protein status.

Main Results:

• A compound heterozygous mutation (p. G492R/p. F610C) in the CAPN1 gene was identified in SMA4 patients.
• Reduced CAPN1 protein levels and protease activity were observed in patient-derived fibroblasts.
• SMN protein levels and subcellular distribution were unaffected, indicating a CAPN1-specific pathology in SMA4.

Conclusions:

• Calpain-1 (CAPN1) is identified as a novel gene associated with the Spinal Muscular Atrophy type 4 (SMA4) phenotype.
• This finding expands the spectrum of disorders linked to CAPN1 mutations.
• The study highlights the tissue-specific role of CAPN1 dysfunction in SMA4 pathophysiology.