Muscles and skeleton
Genes and upbringing determine how our bodies grow
Our physical form is governed principally by our skeleton and musculature, and both are constructed according to the plans laid out in our genes.
Genetic variations can affect skeletal development by altering the balance of bone production and recycling. Altered alleles on the SOST gene, for example, eliminate a negative regulator of bone growth known as sclerostin, leading to excessive bone growth (sclerosteosis). This is seen in various disorders, including van Buchem disease.
Similarly, mutation of muscle proteins can affect muscle form – as in the various types of muscular dystrophy. The regulator of muscle mass is a protein known as myostatin. Human mutations in myostatin are very rare – though a German boy has inherited altered myostatin alleles from both his parents, and has very highly developed musculature.
There is plenty of scope for environmental input, though, particularly through nutrition. The bow-legs of rickets used to be a common sight in the UK, and there are fears that it may return if children are not exposed to enough sunlight to manufacture vitamin D or if babies do not get sufficient amounts from their mother. The risks are highest for some ethnic minority populations, as dark skin blocks the sun’s action, and clothes covering more of the skin, worn for cultural or religious reasons, may also limit exposure to sunlight.
Exercise can help to strengthen both bones and muscle. Impact exercise can increase bone density and protect against osteoporosis in later life. As any body-builder knows, regular weight training can enhance muscle physique. However, even here genes exert an influence – several genetic variants have been found to influence the effects of resistance exercise. (See our ‘Exercise, Energy and Movement’ issue for more.)