Expanding the spectrum of SPTLC1-related disorders beyond hereditary sensory and autonomic neuropathies: A novel case of the distinct "S331 syndrome".

Hereditary sensory and autonomic neuropathies (HSAN) encompass a group of peripheral nervous system disorders characterized by remarkable heterogeneity from a clinical and genetic point of view. Mutations in SPTLC1 gene are responsible for HSAN type IA, which usually starts from the second to fourth decade with axonal neuropathy, sensory loss, painless distal ulcerations, and mild autonomic features, while motor involvement usually occur later as disease progresses. Beyond the classic presentation of HSAN type IA, an exceedingly rare distinct phenotype related to SPTLC1 mutations at residue serine 331 (S331) has recently been reported, characterized by earlier onset, prominent muscular atrophy, growth retardation, oculo-skeletal abnormalities, and possible respiratory complications. In this report, we describe clinical, instrumental, and genetic aspects of a 13-year-old Sri Lankan male carrying the rare de novo p.S331Y heterozygous mutation in SPTLC1 gene found by whole exome sequencing. Patient's phenotype partly overlaps with the first case previously reported, however with some additional features not described before. This work represent the second report about this rare mutation and our findings strongly reinforce the hypothesis of a clearly distinct "S331 syndrome", thus expanding the spectrum of SPTLC1-related disorders.