Novel genetic variation increases chances of baldness

Two independent studies have uncovered a genetic variation that increases a man's chances of developing baldness. Professor Tim Spector at Kings College London, UK, and Professor Axel Hillmer at the University of Bonn, Germany, are the first to use a gene-hunting technique in order to identify traits associated with male pattern baldness (MPB), a form of alopecia. The reports are published side-by-side in the journal Nature Genetics.

MPB affects two thirds of men by the age of 60, and involves hair loss in a well-defined pattern, resulting in a characteristic 'M' shaped hairline. Whilst not unanimously perceived as an affliction, the condition is a major economic burden worldwide, and can be a cause of low self-esteem and social shyness. Thus the ability to predict its appearance has been hailed as a significant scientific breakthrough.

A SNP (single nucleotide polymorphism, a genetic mutation affecting a single DNA base-pair) in the gene for a hormone receptor has previously been associated with MPB. Now, amongst a group of five new SNPs discovered, Professors Hillmer and Spector have agreed upon one as being significant. It seems that co-inheritance of the two mutations (an event seen in one seventh of the population) increases the risk of developing MPB by 70 per cent.

The finding solves a question that has long puzzled scientists. Whilst obvious that some element of MBP is passed on from father to son, the only genetic determinant previously known is found on theX chromosome, which in men is always maternally-inherited. The new SNP lies within chromosome 20, of which there are two copies; one is paternally derived.

The biology of the hormone receptor mutation is well-understood. Levels of the hormone, related to testosterone, fluctuate unnaturally in the blood vessels that feed the scalp. This leads to hair-thinning. How the new SNP might contribute to MPB is unknown. 'We've only identified a cause', says Dr Brent Richards at Kings College London, who also participated in the study. 'Treating male pattern baldness will require more research. But, of course, the first step in finding a way to treat most conditions is to first identify the cause'.

The multiple cohorts of participants were focussed on Switzerland, the UK, the Netherlands and Iceland. Thus only Caucasians were represented. 'I would presume male pattern baldness is caused by the same genetic variation in non-Caucasians', said Dr Brent, 'but we haven't studied those populations, so we can't say for certain'.