Key phenotypic features of Bjornstad Syndrome - both of the following:
(1) congenital sensorineural hearing loss
(2) pili torti, with twisted and brittle hair. A hair shaft is flattened at irregular intervals and twisted 180 degrees from the normal axis
Some patients may have additional findings suggesting a mild complex III deficiency:
(1) growth retardation
(2) developmental delay
(3) profound hypotonia
The patients do not display the multisystem organ dysfunction seen with other syndromes with mutations in BCS1L.
Inheritance: autosomal recessive
Chromosome location: 2q34-36.
Gene: BCS1L
Gene product: a mitochondrial inner-membrane protein that is a member of the AAA family of ATPases. It acts as a chaperone protein in the assembly of mitochondrial respiratory chain complex III.
The mutations in patients with Bjornstad Syndrome affect protein-protein interactions without altering ATP-binding residues.
In classic BS increased amounts of reactive oxygen species are generated by complex I within mitochondria, resulting in oxidative stress to structures such as the hair follicle and inner ear.
