One in 4,500 people suffer from a group of conditions known as sex development disorders (DSD) which occur when the sex chromosomes do not match the genitalia.
DSD can result in defects in the sexual characteristics of a baby, where the gender at birth is not clearly male or female, or where the physical sex of the person does not match the sex of their chromosomes (i.e.. XY females and XX males).
In the majority of DSD cases the underlying genetic mutations are unknown.
Now Australian researchers have discovered how a change to one gene halts the process of an embryo becoming a boy and they believe their research could lead to improved genetic diagnoses, counseling and treatment options.
Some DSD children are born with ambiguous or incomplete genitalia, making it difficult to identify gender while others develop female genitalia despite being genetically male and are raised as girls.
The disorder which is usually only diagnosed at puberty, when girls do not begin to menstruate, renders many DSD sufferers infertile because their internal sex organs are not fully developed.
A team at Prince Henry's Institute (PHI) in Melbourne have discovered in the laboratory how an extra copy of a gene on the X chromosome stops testicles developing in babies who are genetically male.
The researchers found that when they increased the presence of the gene, called DAX1, in cells grown in a laboratory, the cells reduced production of a protein critical for testicle formation which in turn prevents the production of testosterone, which is necessary for the development of the penis.
The researchers say they hope their research will help parents and help experts offer the best treatment options, whether it be hormonal therapy or a surgical therapy.
The PHI researchers hope the discovery of the genes responsible for DSD disorders will allow them to map the 80 per cent of cases that remain unexplained genetically.