Biallelic variants lead to a neurodevelopmental phenotype with gradual neurological impairment.

Biallelic variants in NADH (nicotinamide adenine dinucleotide (NAD) + hydrogen (H))-ubiquinone oxidoreductase 1 alpha subcomplex 13 have been linked to mitochondrial complex I deficiency, nuclear type 28, based on three affected individuals from two families. With only two families reported, the clinical and molecular spectrum of NADH-ubiquinone oxidoreductase 1 alpha subcomplex 13related diseases remains unclear. We report 10 additional affected individuals from nine independent families, identifying four missense variants (including recurrent c.