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NZ Family Provides Clues To Gene "Switch" In Intersex Babies

Fuseworks Media
Fuseworks Media
Harry Ostrer
Harry Ostrer

Wellington, Nov 3 NZPA - An international team of scientists have pinpointed a genetic "switch" in a New Zealand family with inherited "intersex" conditions, where biologically male or female children display some of the physical characteristics of the opposite sex.

Human genetics programme director Harry Ostrer at New York University's Langone medical centre spent nine years with his team exploring the potential impact of a gene labelled MAP3K1 on intersex conditions, through genetic analysis of the New Zealand family and a French family, and two sporadic cases.

"We have discovered a new molecular switch that seems to modulate the pathways between male and female development," Dr Ostrer, said in a statement. The findings were reported today in the American Journal of Human Genetics.

Some researchers believe the MAP3K1 gene may act as a controlling on/off switch, effectively prompting or discouraging an intersex condition.

"MAP3K1 may hold the key to understanding how these various genes are connected," Dr Ostrer noted.

About one in 1000 people are affected by intersex conditions.

Normally, male babies are distinguished by a pairing of an X chromosome alongside a Y chromosome, while female babies are determined by a pairing of two X chromosomes.

But problems occur when a male baby born with an X/Y pairing nonetheless develops some physical attributes of a female child, such as a urethral opening on the underside of the penis or abnormalities such as an underdeveloped or extremely small penis.

Such Y-chromosome intersex children may develop as females but without the ability to menstruate, with partially developed ovaries, an overdeveloped clitoris, excess hair, or ovarian tumours, the research team noted. Infertility can also result.

Mutations in MAP3K1 emerged in individuals with XY chromosomes, but female physical development, in two of 11 sporadic cases and both families with inherited cases.

But the pathway now also appears to play an important role in normal testicular development, mediating the balance between male and female hormonal signals to determine which genitalia the body will produce, researchers explained online in the American Journal of Human Genetics.

Previously-known genetic mutations -- whether a single gene, such as the "master" gene SRY on the Y chromosome, or even omission of an entire chromosome -- account for only a minority of intersex cases.

The MAP3K1 findings will mean more affected individuals will get a reason for their disorder, and XY females should be routinely tested for mutations in the MAP3K1 gene, his team recommended.

Once the cause of a sex development disorder is found, he suggested, other family members should be tested, since the abnormal gonadal tissue left in the abdomen may increase their risk of cancer.

The French family -- in which six women had XY chromosomes and complete or partial gonadal deformation and four men had genital abnormalities -- discovered three women had gonadal tumours.

After gene sequence analysis turned up an unidentified variant in MAP3K1, the researchers sequenced the gene in a second family from New Zealand, also of European descent, with five XY females with complete gonadal deformation.

All members of both families had normal SRY genes.

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