Recessive mutations in the alsin gene cause three clinically distinct motor neuron diseases: juvenile amyotrophic lateral sclerosis (ALS2), juvenile primary lateral sclerosis (JPLS) and infantile-onset ascending hereditary spastic paraplegia (IAHSP). A total of 23 different ALS2 mutations have been described for the three disorders so far. Most of these mutations result in a frameshift leading to a premature truncation of the alsin protein. We report the novel ALS2 truncating mutation c.2761C>T; p.R921X detected by homozygosity mapping and sequencing in two infants affected by IAHSP with bulbar involvement. The mutation c.2761C>T resides in the pleckstrin domain, a characteristic segment of guanine nucleotide exchange factors of the Rho GTPase family, which is involved in the overall neuronal development or maintenance. This study highlights the importance of using homozygosity mapping combined with candidate gene analysis to identify the underlying genetic defect as in this Saudi consanguineous family.
Keywords: ALS2; Alsin-2 gene; Amyotrophic lateral sclerosis; DH/PH; Db1 and pleckstrin homology; GDP; GEF; GTP; GTPase; Hereditary spastic paraplegia; Homozygosity; IAHSP; JPLS; LMN; MORN; Motor neuron; Mutation; RCC1; ROH; Ras homologous member; Rho; UMN; VPS9; guanine exchange factor; guanosine diphosphate; guanosine triphosphatase NMD: nonsense-mediated mRNA decay; guanosinetriphosphatase; infantile-onset ascending hereditary spastic paraplegia; juvenile amyotrophic lateral sclerosis 2; juvenile primary lateral sclerosis; lower motor neurons; membrane occupation and recognition nexus; regions of homozygosity; regulator of chromatin condensation 1; upper motor neurons; vacuolar protein sorting 9.
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