Two siblings with galactose mutarotase deficiency: Clinical differences.

Galactose mutarotase (GALM) deficiency is an inherited metabolic disease caused by the deficiency of the first enzyme in the Leloir pathway. GALM deficiency was first reported in 2018. To date, eight cases have been reported. We are presenting two siblings with GALM deficiency; one patient presented with cataracts and her brother was asymptomatic. We evaluated the first case due to a cataract at 3 months old. She had elevated galactose and galactose-1-phosphate and normal galactose-1-phosphate uridylyltransferase (GALT) activity. Genetic analysis and other laboratory and clinical findings excluded galactokinase-1 (GALK1) and UDP-galactose 4'-epimerase (GALE) deficiencies. She had a homozygous mutation p. Gly277Arg (c.829G>A) in the GALM (NM_138801) gene. She was 3 years old at the last visit, and her physical examination was normal, except for cataracts. The same mutation was found to be homozygous in the patient's asymptomatic sibling during family screening. He had normal blood galactose and galactose-1-phosphate. This study highlights the importance of evaluating the whole galactose metabolism in terms of GALM deficiency in patients with cataracts.