CHARACTERIZATION OF DISEASE GENES IN NEURODEGENERATION WITH BRAIN IRON ACCUMULATION

Neurodegeneration with brain iron accumulation (NBIA) comprises a heterogeneous group of genetically defined disorders clinically characterized by progressive extrapyramidal deterioration and by iron accumulation in the basal ganglia. The clinical spectrum of NBIA is extremely wide and includes early-onset neurodegeneration and adult-onset parkinsonisms-dystonia. Recessive NBIA syndromes may be due to mutations in the PANK2, PLA2G6, FA2H, and C19orf12 genes, but still in a large proportion of patients, no genetic alteration can be found. Using Whole Exome Sequencing (WES) strategy we identified, in a NBIA patient, a homozygous missense mutation in the gene codifying for coenzyme A synthase (COASY). By performing traditional Sanger sequencing in a cohort of NBIA subjects, we found another mutant patient. COASY is a bifunctional mitochondrial enzyme involved in the two last steps of coenzyme A (CoA) biosynthesis, a molecule of primary importance for several metabolic pathways. The missense mutation found affects a highly conserved aminoacid residue in the catalytic site of COASY. Western-blot analysis showed that the protein is absent in patients-derived skin fibroblasts. We synthesized human wild-type and mutated catalytic domain and full-lenght COASY to analyze, by HPLC, in-vitro protein activity. Additional experiments were performed on yeast cells and on patient-derived skin fibroblasts. Together with mutations in PANK2, coding for the first enzyme involved in CoA biosynthesis, mutations in COASY impinge on the same biosynthetic pathway causing NBIA. For this reason further analysis were performed also on PKAN patients-derived skin fibroblasts and on Pank2 knockout mouse model, to better understand the link between CoA synthesis defect and neurodegeneration.