For one family, a young girl’s diagnosis with a rare genetic disease ended years of tests and referrals to explain her puzzling symptoms: an overgrowth of fatty tissue on specific parts of her body including her belly and one leg.

For the researchers who made the diagnosis, it provides insight into a rare, poorly understood disease and may shed light on the genes that cause obesity.

“This case illustrates how studying rare genetic diseases can inform our understanding of common diseases,” says Dr. William Gibson, the lead author on the study. “Improving our understanding of fibroadipose hyperplasia may help to explain why some fat deposits grow more than others, even in patients without this rare genetic mutation.”

Dr. Gibson is a Senior Clinician Scientist at the Child & Family Research Institute at BC Children’s Hospital, Medical Geneticist at BC Children’s and an Associate Professor in the Department of Medical Genetics at the University of British Columbia.

Fibroadipose hyperplasia is caused by a mutation in a gene called PIK3CA. Fewer than 1 in 1 million people are estimated to have the disease. Because it was discovered recently, every new case provides fresh insights into the nature of the disease and may help doctors diagnose fibroadipose hyperplasia in other children.

“For rare diseases, getting the right diagnosis is critical to getting the best possible care, and that often means research-based diagnostic tests like the one we used here,” says Dr. Gibson. “We hope that this family’s story will raise awareness of fibroadipose hyperplasia and how we can diagnose it better.”

For the young girl with fibroadipose hyperplasia, this diagnosis means the family no longer has to worry that their daughter will need surgery to remove the excess belly fat. Previously, her doctors were worried that her belly fat might turn into a more aggressive tumour, but now they know that this is very unlikely because that tends not to happen in patients with PIK3CA mutations.

This research was recently published in the American Journal of Medical Genetics. Genetic testing was done in collaboration with by Dr. Stephen Yip, Neuropathologist at Vancouver General Hospital and Assistant Professor in the Department of Pathology at UBC.

This study was funded by an operating grant from the Canadian Institutes of Health Research and by a microgrant from the Rare Disease Foundation.

For more information:

Somatic mosaicism for the p.His1047Arg mutation in PIK3CA in a girl with mesenteric lipomatosis, William Gibson et al., American Journal of Medical Genetics, June 5, 2014