Respiratory Disease and CHD Linked Through Genes

A study by researchers at the University of North Carolina Chapel Hill School of Medicine has found that a common genetic defect might be responsible behind a rare respiratory disease and some types of congenital heart disease (CHD). The findings have been published in the journal Circulation.

The connection was first noticed by researchers in children with primary ciliary dyskinesia (PCD), a respiratory disease that affects cilia. These are the tiny hair-like extensions that help the lungs clear of mucus and remove contaminants such as dust. The disease is caused when movement of these cilia becomes impaired due to genetic mutation.

The researchers observed that some of the children treated for PCD and UNC-Chapel Hill also suffered from heterotaxy. This is a condition associated with congenital heart disease in which the heart and lungs are in an abnormal position. The observation led them to wondering if PCD and heterotaxy were related because certain other types of cilia called nodal cilia, are believed to play an important part in directing and organizing organs in a developing embryo.

To confirm their suspicions the researchers studied 337 patients with PCD. Of these, 6.3% or 21 children also had heterotaxy. When the researchers carried out genetic testing on 12 of the patients with heterotaxy, they found that seven of them also had one of two genetic mutations known to cause PCD.

This led researchers to the conclusion that the link between the two diseases starts with cilia. They found that people with PCD had 200 times higher incidence of heterotaxy and congenital heart defects than in the general population (one in 50 as against one in 10,000).

“This should spur physicians treating patients with congenital heart disease to be more vigilant about testing for and treating respiratory defects,” said Dr. Michael R. Knowles, Professor of Pulmonary and Critical Care Medicine and study senior author. “It is critical for families and physicians to recognize when congenital heart disease develops.”

“Children with both heterotaxy and congenital heart disease typically undergo surgery to repair heart defects, and if they have respiratory complications after surgery, it’s often assumed that the cause is their heart problems,” Knowles said. Their study however indicates that the respiratory problems might also be on account of an underlying genetic cause.

“Now when we see a patient with heterotaxy and a heart defect, then we’re going to know to look for ciliary dysfunction,” said Dr. Blair V. Robinson, Clinical Associate Professor of Pediatrics at UNC-Chapel Hill and an author of the study. “In addition, the associations between ciliary function, the heart defects and the organization of organs in the chest and abdomen will hopefully lead to better understanding of how these defects develop.”

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