Bilateral retinal dystrophy and unilateral hearing loss caused by mosaic phosphoribosyl pyrophosphate synthetase 1 deficiency: expanding the spectrum of an ultrarare neurometabolic disorder

Background: Phosphoribosyl pyrophosphate synthetase 1 (PRPS1) deficiency is a rare neurometabolic disorder with wide spectrum of presentation. It can present in early childhood with global developmental delay, retinal dystrophy, and hearing loss, or can present as isolated neuropathy or hearing loss in adulthood. Here we describe a patient with vision impairment, fatigue, and unilateral hearing loss caused by a somatic mosaic pathogenic variant in PRPS1 gene which encodes PRPS1. Supplementation with S-adenosylmethionine (SAMe) and Nicotinamide Riboside (NR) resulted in improvement in symptoms. Method and results: This retrospective clinical-laboratory observational study has a reference patient who was found to have right-sided hearing loss and vision impairment in right eye in early childhood. Later on, he developed epilepsy. He had deterioration in cognitive function in adolescence. At the age of 26 years, he developed progressive vision impairment due to bilateral, asymmetric retinal degeneration. In addition, he had severe generalized fatigue. Molecular diagnostic workup showed a mosaic pathogenic variant c.383A > T, p. Asp128Val in PRPS1. Subsequently, SAMe at 800mg twice a day and NR at 800 mg daily doses were started leading to significant improvement in fatigue and stabilization of vision. Conclusion: PRPS1 deficiency is an inherited disease of nucleotide biosynthesis. The age of onset of symptoms as well as severity of symptoms are variable. Supplementations with nucleotide precursors may stabilize the clinical course.