Distal Hereditary Motor Neuropathy Type II (Distal HMN Type II): Phenotype and Molecular Genetics

Area of Science:

• Genetics
• Neurology
• Molecular Biology

Background:

• Distal hereditary motor neuropathies (distal HMN) are a group of rare, inherited neurological disorders characterized by progressive muscle weakness and sensory loss, primarily affecting the distal extremities.
• These neuropathies exhibit significant clinical and genetic heterogeneity, necessitating detailed genetic mapping to identify causative genes.
• Autosomal dominant distal HMN type II presents with a phenotype similar to Charcot-Marie-Tooth disease, with onset typically between 15 and 25 years.

Purpose of the Study:

• To identify the genetic basis of autosomal dominant distal HMN type II in a multigenerational Belgian pedigree.
• To investigate the chromosomal location of the responsible gene and explore potential candidate genes.

Main Methods:

• Genome-wide linkage analysis was performed on affected family members.
• Microsatellite markers, including D12S86 and D12S340, were used to narrow down the chromosomal region.
• Positional candidate gene screening, including the human pancreatic phospholipase A2 (PLA2A) gene, was conducted.

Main Results:

• Significant linkage was established to chromosome 12q24.3, specifically between markers D12S86 and D12S340.
• The human pancreatic phospholipase A2 (PLA2A) gene was identified as a positional candidate but initial screening did not reveal disease-causing mutations in its coding region.
• A yeast artificial chromosome (YAC) contig map of the candidate region was constructed to facilitate gene isolation.

Conclusions:

• A novel locus for distal HMN type II has been mapped to chromosome 12q24.3.
• The gene responsible for distal HMN II in this family is likely located within this region, but PLA2A is not the causative gene.
• Ongoing screening of positional and functional candidate genes is crucial for identifying the specific mutation responsible for distal HMN II.