In some patients with gigantism, scientists have discovered a duplication of a short stretch of the X chromosome, according to a study from the National Institute of Child Health and Human Development (NICHD). It is believed that one gene within the region largely impacts how much children grow.

In the mid-1990s, a family had come to the NIH Clinical Center for treatment. The mother had been treated for gigantism, and her two sons were also growing rapidly. Another family from Australia came to the Center with an affected daughter. Researchers noted the same duplication that was seen in the first family. The same duplication was also found in a group of patients in Belgium.

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Researchers used whole-genome analysis to detect major changes in the DNA of 43 people with gigantism. The same duplication of a stretch of the X chromosome was found in every study participant who had gigantism as an infant or a toddler. Family members without gigantism, however, did not exhibit this duplication. The length of DNA duplication was different among the patients, but the same four genes that were duplicated in all patients were identified. After further testing, a gene called GPR101 was isolated as the most probable cause. GPR101’s activity was up to 1,000 times stronger in the children with the duplication than in normally developing children.

In patients with acromegaly, none of the patients displayed the duplication that was seen in patients with gigantism. Eleven of the patients with acromegaly did have a mutation in GPR101, which may imply the gene’s role in this condition as well.

Future studies will be based on understanding how the protein that is derived from GPR101 works.

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