A rare case of primary coenzyme Q10 deficiency due to COQ9 mutation.

Background Coenzyme Q10 (CoQ10) serves as a shuttle for electrons from complexes I and II to complex III in the respiratory chain, and has important functions within the mitochondria. Primary CoQ10 deficiency is a mitochondrial disorder which has devastating effects, and which may be partially treated with exogenous CoQ10 supplementation. Case presentation A 9-month-old girl patient was referred to our clinic due to growth retardation, microcephaly and seizures. She was the third child of consanguineous parents (first-degree cousins) of Pakistani origin, born at 38 weeks gestation, weighing 2000 g after an uncomplicated pregnancy, and was hospitalized for 3 days due to respiratory distress. She had sustained clonic seizures when she was 4 months old. Physical examination showed microcephaly, truncal hypotonia and dysmorphic features. Metabolic tests were inconclusive. Abdominal ultrasonography revealed cystic appearance of the kidneys. Non-compaction of the left ventricle was detected in echocardiography. Cranial magnetic resonance imaging (MRI) showed hypoplasia of the cerebellar vermis and brain stem, corpus callosum agenesis, and cortical atrophy. A panel testing of 450 genes involved in inborn errors of metabolism (IEM) was performed that showed a novel frameshift c.384delG (Gly129Valfs*17) homozygous mutation in COQ9. A treatment of 5 mg/kg/day exogenous CoQ10 was started when she was 10 months old, and the dosage was increased to 50 mg/kg/day after the exact diagnosis. No objective neurological improvement could be observed after the adjustment of the drug dosage. Conclusions We report a case of CoQ10 deficiency due to a novel COQ9 gene mutation that adds clinical data from a newly diagnosed patient. Our case also outlines the importance of genetic panels used for specific diseases including IEM.