What is Poly-T?

Poly-T refers to a group of genetic mutations which cause the disease cystic fibrosis. Cystic fibrosis is caused by an autosomal recessive genetic mutation which results in a sticky mucosal buildup, primarily in the lungs but also in other organs such as the pancreas, kidneys, liver and digestive tract.

Individuals with cystic fibrosis inherit mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. There are two copies of every autosomal gene (genes that are not on the XY chromosomes) and as the disorder is autosomal recessive, both copies must be deficient to result in disease. Individuals with one mutated CFTR gene and one functional gene do not exhibit symptoms and are known as carriers. Offspring of two carriers have a 25% chance of inheriting two faulty genes and developing cystic fibrosis, 50% chance of being a carrier and 25% chance of having two functional copies of the gene.

There are several different potential mutations which can result in a faulty CFTR gene. Among known mutations are 5T, 7T and 9T variants, referred to as polythymidine (Poly-T). These mutations have been shown to modulate the severity of the disease when in combination with the R117H mutation on the second copy of the gene.

Cystic fibrosis cannot be cured, and lifelong treatments are required to reduce symptoms sufficiently for a relatively normal life. Individuals with cystic fibrosis are also prone to secondary infections.  

Why take the test?

This test screens for poly-t mutations of the CFTR gene. It is typically used to see if you are a carrier of any of these mutations but can be used to diagnose the exact genetic cause of cystic fibrosis in an individual.