Polyarticular Arthritis and Spinal Muscular Atrophy in Acid Ceramidase Deficiency

Survival of motor neuron 1---negative spinal muscular atrophy (SMA) is heterogeneous and remains a diagnostic challenge. The clinical spectrum continues to expand and ∼33 genes have been identified to date. The present report describes a 9-year-old girl with novel clinical phenotype of a patient with polyarticular arthritis followed by symptoms of SMA due to acid ceramidase deficiency. Whole exome sequencing identified compound heterozygous pathogenic mutation in the N-acylsphingosine amidohydrolase 1 gene. Functional assay with leukocyte acid ceramidase activity showed a decreased level in the proband confirming pathogenicity of the mutations. Mutations of N-acylsphingosine amidohydrolase 1 are known to separately cause Farber disease (arthritis, subcutaneous nodules, and dysphonia) or SMA with progressive myoclonic epilepsy. The present combined phenotype is novel, bringing together SMA with progressive myoclonic epilepsy and Farber disease and establishing a phenotypic spectrum. Acid ceramidase deficiency is an important consideration in patients presenting with polyarticular arthritis and motor neuron disease.