Extra-gene babies 'relatively common'

The presence of an extra copy of a human sex gene can transform an embryo from boy to girl and produce genitalia that doctors cannot determine to be male or female, research has shown.

Researchers at the University of California, Los Angeles (UCLA), say babies born with this condition are relatively common.

They hope their findings, published in the American Journal of Human Genetics, will help doctors to ascertain more accurately and quickly the sex of these babies and perhaps lead to ways of correcting the defect before birth.

The study shows that mild cases of malformed genitalia such as undescended testes or an enlarged clitoris are seen in 1 per cent of all births.

More severe cases, in which babies are born with such sexually ambiguous genitals that obstetricians cannot discern the sex of the infant, occur in one out of 3000 births.

Dr Eric Vilain and colleagues at UCLA pinpointed WNT-4, a signalling gene on human chromosome 1, as one of a handful of genes known to determine a human's sex.

Unlike classic genetic defects that result from the absence or mutation of a gene, genital malformations occur when WNT-4 appears twice, rather than the normal once, on the chromosome.

"Genital malformations are an unspoken yet frequent public health problem," Dr Vilain said. "Parents don't speak of it because they fear others will consider their children taboo or shameful."

The researchers plan to study whether it would be possible to lower the chromosomal dose of WNT-4 in the embryo of a pregnant woman who already has had a baby with malformed or ambiguous genitalia.

"Our findings suggest that clinicians could identify the WNT-4 duplication prenatally. If this proves true, we may be able to correct the defect in the womb and restore the embryo to its original male status."

- REUTERS