The key to eternal youth?

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Four Turkish families have helped researchers solve a long-standing mystery about the biological basis of puberty.

The distantly related families include seven children who grew into their teens and 20s without ever reaching puberty. (Another child, a 5-year-old girl, isn’t expected to hit puberty either.) The rare condition is called normosmic idiopathic hypogonadotropic hypogonadism, or nIHH.

A team of scientists from Cukurova University in Adana, Turkey, and the University of Cambridge in England looked for single-letter mutations in their DNA. They zeroed in on two key genes that appear to activate the cascade of hormones that allow adolescents to reach sexual maturity.

In three of the families, affected children had two faulty versions of a gene called TACR3. In the fourth family, two affected siblings had normal TACR3 genes but inherited defective versions of a related TAC3 gene from both parents. A normally functioning TAC3 gene contains instructions for making a peptide called neurokinin B, and TACR3 codes for the neurokinin B receptor.

The researchers surmised that neurokinin B plays the crucial role of instructing the brain to produce gonadotropin-releasing hormone. That, in turn, prompts the release of other hormones that ultimately stimulate the testes to secrete androgens and testosterone or the ovaries to make estrogen and progesterone.

Writing this week in the journal Nature Genetics, the researchers said the discovery helps answer “an enduring enigma of human biology.” The findings could not only help treat nIHH but aid development of new drugs to treat infertility and diseases related to sex steroids, including breast and prostate cancer.