There are some well-known genetic traits to which men are more susceptible than women simply because they have one X chromosome. These X-linked disorders include red-green colour blindness, haemophilia, muscular dystrophy and IPEX syndrome, which affects immune function. Mental retardation, which affects 2 to 3 per cent of people in developed countries, and significantly more men than women, also has a strong link to the X chromosome.
