Autism and the X Chromosome

Autism “sits” on the X chromosome, on which more genetic diseases have indeed been found, according to Female chromosome has X factor, an article in today’s BBC news. The X chromosome contains 1,098 genes, while the Y chromosome contains only 78. That is, female mammals have over 1,000 more genes than males and, to compensate, “the female body switches off one X chromosome – quite randomly – in each cell, thus evening up protein production between the sexes.” And, because males have only a single X chromosome, diseases located on it (including “nasty diseases and disorders” like haemophilia, autism, muscular dystrophy and mental retardation) are more likely to be expressed:

…..because females have another – usually healthy – copy of the X chromosome, they are usually shielded from the full impact of these disorders. Males, on the other hand, who have nothing to fall back on, are forced to fully express their faulty genes.

“Because males have only a single X chromosome, more genetic diseases have been found on this chromosome than any other,” said Dr Ian Jackson of the MRC Human Genetics Unit, UK. “One consequence is that boys have a higher incidence of mental retardation than girls.

The BBC news article also notes that males are more likely to be at the extremes of intelligence: “if you have very good intelligence genes on your X chromosome, it pays not to have them muffled by more average genes on another X chromosome.” Professor Mike Stratton, of the Wellcome Trust Sanger Institute, notes that by knowing about what genes on the X chromosome are “harmful,” the onset of mental retardation might be prevented. (This article seems to lump together autism and mental retardation, so the previous statement might be read as suggesting that the onset of “nasty diseases and disorders” like haemophilia and autism might be prevented.)

Go here to read Female chromosome has X factor.