C9orf103 (chromosome 9 open reading frame 103), also known as gluconate kinase, is a 187 amino acid protein that belongs to the gluconokinase gntK/gntV family and catalyzes the conversion of ATP and D-gluconate to ADP and 6-phospho-D-gluconate. Existing as three alternatively spliced isoforms, the gene encoding C9orf103 maps to human chromosome 9q21.32. Chromosome 9 consists of about 145 million bases, represents 4% of the human genome and encodes nearly 900 genes. Thought to play a role in gender determination, deletion of the distal portion of 9p can lead to development of male to female sex reversal, the phenotype of a female with a male X,Y genotype. Hereditary hemorrhagic telangiectasia, which is characterized by harmful vascular defects, is associated with the chromosome 9 gene encoding endoglin protein, ENG. Familial dysautonomia is also associated with chromosome 9 though through the gene IKBKAP. Notably, chromosome 9 encompasses the largest interferon family gene cluster.