Björnstad syndrome is a congenital condition involving deafness and hair abnormalities.

It is thought to be an autosomal recessive disorder closely related to Björnstad syndrome which presents similarly but without hypogonadism.

However, mutations in BCS1L, a gene responsible for proper maturation of Complex III, can result in Björnstad syndrome and the GRACILE syndrome, which in neonates are lethal conditions that have multisystem and neurologic manifestations typifying severe mitochondrial disorders.