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Monday, May 25, 2009

A 31-year-old Chinese man whose body is 96 per cent coated in hair has an
extra chunk of DNA that could explain his condition – called congenital
generalized hypertrichosis terminalis (CGHT).

A new study of the patient known as "KK" – one of the world's hairiest men –
and three families with a history of CGHT suggests that the disease is caused
by vast genomic changes on chromosome 17.

CGHT is exceedingly rare, with fewer than 100 cases documented in news reports
and the scientific literature, says Xue Zhang, a geneticist at Peking Union
Medical College in Beijing, who led the new study.

The disease is one of at least several forms of hypertrichosis – all
characterised by overgrowth of hair. [...]

To find the genetic changes responsible for CGHT, Zhang's team first scanned
the genomes of 16 people with the disease and their unaffected relatives,
looking for obvious differences.

A region on chromosome 17 jumped out, and after further study, Zhang's team
showed that family members with CGHT were missing between 500,000 and 900,000
DNA letters on that chromosome. Patient KK, on the other hand, had 1.4 million
extra nucleotides at the same place on the genome.

Exactly how these changes cause the disease is unclear, says Zhang. One of the
several genes in this region, MAP2K6, could be involved in hair growth. But
mice missing lacking this gene have normal hair, and a 12-year-old girl
missing this gene shows no signs of CGHT. More likely, the changes on chromosome
17 affect the expression of distant genes, Zhang's team suggests.

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