Natural history of NGLY1 deficiency: motor function & clinical features.

N-glycanase 1 (NGLY1) Deficiency is an ultra-rare neurodevelopmental disorder caused by biallelic loss-of-function mutations in the NGLY1 gene, leading to severe impairments in neurocognitive and motor function abilities in the affected patient population. Its core clinical features include global developmental delay, hyperkinetic movement disorders, elevation of liver transaminases, (hypo)alacrima, and progressive sensorimotor neuropathy. Due to the range of phenotypes and severity within the confirmed patient population, ongoing characterization of the disease is critical. A prospective natural history study (NHS) was conducted to further elucidate disease phenotypes and examine any changes in neurocognitive or motor function over a one-year period. Fifteen participants, representing roughly 10% of the total identified patient population, were enrolled to complete three onsite visits. Participants in this study exhibited phenotypes previously reported, including core disease phenotypes, hypotonia, scoliosis, musculoskeletal abnormalities, abnormal electroencephalogram (EEG) results, and visual and genitourinary abnormalities. Results from validated neurocognitive and motor function assessments revealed profound global developmental delays in all participants, including communication, gross and fine motor function, and cognitive domains. Age-equivalent scores identified a widening developmental gap between participants and neurotypical peers over time, indicating delayed milestone achievement and/or regression. Although fluctuations were observed, measurements for individual participants were mostly stable over the course of the NHS. Liver transaminase and biomarker N-acetylglucosamine-asparagine (GlcNAc-Asn; GNA) levels were elevated in all participants. Results build on previous studies and inform the selection of potential endpoints for emerging interventional clinical trials, including laboratory values, neurocognitive and motor function assessments, and caregiver reported outcomes.