Eight gene-disease pairs were excluded because hearing loss is not a presenting feature of the disease: namely ALMS1/alstrom syndrome, ATP6V1B1/DRTA2, BTD/biotinidase deficiency, COL4A5/alport syndrome, GJB3/erythrokeratodermia variabilis, DSPP/dentinogenesis imperfecta, GJB6/clouston syndrome, and TCOF1/treacher-collins syndrome. The gene discussed is BTD; the disease is biotinidase deficiency.