113 Clinical and neurophysiological improvement in Hereditary sensory and autonomic neuropathy type I (HSAN-1) following high dose serine therapy

Objective To report clinical stabilisation and improved summated compound motor action potentials (CMAP) in a patient with Hereditary sensory and autonomic neuropathy type I (HSAN-1) following high dose serine therapy. Case A 52-year-old male presented in 2006 with a typical HSAN-1c phenotype and over the ensuing years had progressive distal to proximal sensory disturbance, associated lancinating pains, and mild progressive distal predominant limb weakness. A Ser384Phe mutation in the SPTLC2 gene located on chromosome 14q24 was identified in this patient in 2017. In late 2018 high dose serine therapy (11 grams TDS) was commenced, resulting in stabilisation of clinical weakness. Lower limb motor and sensory responses were absent at presentation in 2006 with initial summated bilateral upper-limb median and ulnar nerve CMAP being 31.2mV and steadily declining to 4.2mV in March 2019. Following Serine therapy, the summated CMAP increased to 5.4mV in August 2020 and 9.5mV in February 2021, furthermore previously absent upper-limb sensory nerve responses are now recordable. Conclusions High dose Serine replacement therapy may lead to clinical stabilisation and improved neurophysiological parameters in HSAN-1. HSAN-1, an autosomal dominant sensory neuropathy occurs secondary to mutations in the enzyme Serine-Palmitoyltransferase (SPT), an essential enzyme in the de-novo synthesis of sphingolipids. The administration of high dose Serine may overcome altered SPT substrate specificity in HSAN-1, which preferentially uses L-alanine and L-glycine instead of L-serine and allow the formation of typical 1-deoxysphingolipids as opposed to atypical 1-deoxysphingolipids generally seen in this condition, with early treatment possibly preventing clinical progression.