Biotinidase deficiency is an autosomal recessive inborn error of metabolism in which infants appear normal at birth. However, if untreated, affected infants can develop symptoms including hypotonia, ataxia, seizures, developmental delay, vision and hearing loss and cutaneous problems (eg. alopecia, dermatitis, eczema). Those diagnosed at birth should remain asymptomatic if treatment is initiated early and maintained. Biotinidase deficiency is typically detected very early because of newborn screening programs, which measure biotinidase activity in dried blood spots.