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At a glance

A genetic disorder with pili torti and sensorineural deafness.

Synonyms

BjØrnstad Syndrome; Pili Torti and Nerve Deafness Syndrome; Pili Torti and Sensorineural Hearing Loss Syndrome.

History

The Scandinavian physician R. T. Björnstad first reported eight patients with pili torti and five of them (from several families) with sensorineural hearing loss at the “Proceedings of the 17th Combined Scandinavian Dermatological Association Meeting” in Copenhagen, Denmark in 1965.

Incidence

Probably less than 50 cases have been described.

Genetic inheritance

Inheritance is autosomal recessive with gene map locus on 2q34-36. The genetic defect is caused by homozygous or compound heterozygous mutation in the BCS1L (homolog, ubiquinol-cytochrome c reductase complex chaperone) gene, which has been mapped to chromosome 2q35. To date, less than 15 different mutations in the BCS1L gene are known to cause Björnstad Syndrome. BCS1L encodes a protein of the inner mitochondrial membrane that is a member of the “ATPases Associated with diverse cellular Activities” (AAA) family of ATPases. As such, it is involved in the assembly of mitochondrial complex III where it acts as a translocase for the Rieske iron-sulfur protein (one of three catalytic subunits of complex III) from the cytosol to the inner mitochondrial membrane. Complex III deficiency is associated with neonatal tubulopathy, encephalopathy, and liver failure. Mutations in the BCS1L gene are also responsible for GRACILE Syndrome (Complex III Deficiency), an acronym that stands for Growth Retardation, Aminoaciduria, Cholestasis, Iron overload, Lactic acidosis, and Early death, a disorder mainly found in the Finnish population. All BCS1L mutations, including the ones responsible for Björnstad Syndrome, cause disruption of the assembly of mitochondrial respirasomes (the basic unit for respiration in human mitochondria), but the severity of the clinical expression of the mutations correlates with the production of reactive oxygen species.

Clinical aspects

Impaired hearing is usually already evident in the first years of life, progressive and of variable severity, but seems to stabilize around puberty. Abnormalities of the hair (eg, coarse, dry, lusterless, brittle hair) are already present in the first year of life and mainly of cosmetic concern. In some cases, the hair anomalies are accompanied by partial or almost total alopecia, while other patients have no signs of sparse hair. Microscopic examination of the hair shaft reveals flattening at irregular intervals and a 180-degree (or more) twisting around its axis and partial trichorrhexis (fractured hair shafts with the ends stuck together resembling broomsticks. Diagnosis is confirmed by optical and scanning electron microscopy. Compared to normal hair, the hair shaft diameter is flattened and twisted (pili torti), which causes the hair to be brittle and break easily. The defect can be observed under microscopy within the endocuticle layer. The calculated tensile ...

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