बुधवार, जनवरी 17, 2007

Here's what I found in today's "Deccan Chronicle" -

DISCOVERY - Found: Fully functional man with female genes:
A person with XX chromosomes is a woman, while XY chromosomes mark out a man. But scientists have come across a man with female XX chromosomes who is sexually functional. This is rare since men with XX chromosomes, who are one in about 25,000, do not have male characteristics.

Scientists speculate that an unknown gene could have mutated and lost its sex-determination function, or from a mutation in a gene in the Sex-determining Region (SRY). SRY however is not the only, or even the most common sexdetermining gene.

Mr XX, whose identity is being withheld, turned up at the genetic clinic of the Institute of Reproductive Medicine, Kolkata, with complaint of infertility. He is 156 cm and weighs 64 kg. He had fully mature normal male genitalia with no symptom of undervirilisation. Among others, he had normal levels of testorone hormone, smaller testicles but elevated levels of serum concentrations of reproductive hormones.

No one knows how Mr XX could be a fully functional man with a woman’s genes. Kumarasamy Thangaraj, senior scientist at the Hyderabad-based Centre for Cellular and Molecular Biology (CCMB), where Mr XX’s data landed up, said, “Despite the identification of SRY almost 15 years ago, the pathway downstream to SRY remains largely unknown.” According to the CCMB study, an increasing number of reports suggest that the male trait can develop even in the absence of SRY. Such persons exist in three categories: XX males with normal genitalia; XX males with ambiguous genitalia; and XX true hermaphrodites with ovarian and testicular tissues.

Dr Thangaraj says the existence of SRY-negative males ruled out the notion that mere presence of SRY determines maleness.

The most common observation that the individuals are male shows that it is the presence or absence of a normal SRY gene which determines maleness, provided all downstream genes are intact.

In majority of the cases, XX maleness should result either from the loss of function mutations in a gene normally inhibiting testes formation in females or from the gain of function mutations in a gene downstream to SRY in testis determining pathway.

The hypothetical gene may be X-linked or autosomal (non-sex chromosome). If the gene is autosomal, the degree of the male trait will be dependent on the extent of the loss or gain of function in the mutant gene, Dr Thangaraj says.

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