Current and Emerging Treatments for Acid Sphingomyelinase Deficiency.

Acid sphingomyelinase deficiency is an ultra-rare disease characterised by generalised storage of sphingomyelin, caused by deficiency of the lysosomal enzyme acid sphingomyelinase, owing to the presence of biallelic pathogenic variants in the SMPD1 gene. The main disease manifestations are in the liver, spleen, lung and bone - with some patients having also involvement of the central nervous system. Patients show variable degrees of anaemia, thrombocytopenia and lipid abnormalities, among other findings. Clinically, acid sphingomyelinase deficiency spans from an acute neurovisceral form, with neurological involvement and early death (type A), to a chronic visceral disease, with no or minimal neurological manifestations (type B). An intermediate form, with chronic neurovisceral involvement, is presented by some patients (type A/B). Diagnosis involves the measurement of biomarkers, an assay of enzyme activity and genetic testing. Until a few years ago, treatment was mainly dependent on symptomatic management and bone marrow or solid organ (liver and/or lung) transplantation. In 2022, a specific enzyme replacement therapy with olipudase alfa was approved, and the results available indicate that it changed the therapeutic landscape for patients with acid sphingomyelinase deficiency type B and A/B. Research is being developed to address the needs of patients with acid sphingomyelinase deficiency type A, with gene therapy remaining as a promising approach.