Rare genetic variations may solve mystery of porphyria severity in some patients

An international research team has linked rare variations in a cell membrane protein to the wide variation in symptom severity that is a hallmark of porphyria, a rare disorder that often affects the skin, liver and nervous system. St. Jude Children’s Research Hospital helped to lead the research.

Porphyrias are a family of diseases usually caused by inherited mutations in one of the eight enzymes involved in assembling heme. Heme is a molecule that plays a critical role in oxygen transport, drug metabolism and other vital physiological processes. 

In this study, researchers discovered rare variations in the ABCB6 gene, also called Lan. The variations were associated with the toxic build-up in cells of chemicals produced during heme assembly. Investigators reported that the variants were more common in patients with severe porphyria than in those with less severe symptoms.

“One of the mysteries of this disease has been why some individuals with the same genetic defect have mild symptoms while others have severe symptoms and require hospitalization in the intensive care unit,” said corresponding author John Schuetz, Ph.D., a member of the St. Jude Department of Pharmaceutical Sciences. “Using gene sequencing, biochemical analysis and a new mouse model of the disease, we have identified variations in ABCB6 as an unexpected genetic modifier of porphyria severity.”

The discovery followed DNA sequencing of the protein-coding regions, or exomes, of seven porphyria patients with a history of life-threatening symptoms and hospitalization in the intensive care unit. They were among the 36 porphyria patients treated at the Royal Prince Alfred Hospital in Sydney, Australia, included in the study.

Researchers found that five of the seven patients carried rare versions of ABCB6 and made little or no functional ABCB6 protein. Sixty-two percent of patients with the rare ABCB6 variants were admitted to the intensive care unit compared to about 7 percent of other patients.

ABCB6 is carried on the surface of red blood cells, where 85 percent of heme is produced. The protein is one of several proteins that export porphyrins and related molecules from liver, blood and other cells.

Jann Ingmire
St. Jude Children’s Research Hospital www.stjude.org/media-resources/news-releases/2016-medicine-science-news/rare-genetic-variations-may-solve-mystery-of-porphyria-severity-in-some-patients.html