Weill Cornell Researchers Identify Gene That Causes Heart Tumors And Limb Deformity

The mutation causes muscle protein dysfunction and is linked to both a crippling muscle condition and a type of rare heart tumor, Dr. Basson and colleagues report in the July 29 issue of the New England Journal of Medicine. By fingering the one gene connecting these two diverse conditions, the researchers believe they've solved a longstanding medical mystery.

Even more intriguing, the mutation's connection to heart tumors hints at the existence of stem cells within the adult human heart — cells doctors might someday use to repair failing cardiac muscle. Experts have hotly debated the very existence of these cells for decades.

"We've opened the door to a very exciting set of possibilities. Not only was the door closed before — no one even knew the door was there," said Dr. Craig T. Basson, Director of Cardiovascular Research in the Greenberg Division of Cardiology, and Professor of Medicine and Professor of Cell & Developmental Biology at Weill Cornell Medical College. Dr. Basson is also Attending Physician at New York-Presbyterian Hospital/Weill Cornell Medical Center.

The study focused on a rare form of a benign, but still quite dangerous, heart tumor called a myxoma. These types of heart tumors affect about 1 in every 100,000 people, and have genetic roots.

In what's been a medical puzzle, a subset of individuals with cardiac myxomas are also afflicted with a seemingly unrelated muscle disorder called trismus-pseudocamptodactyly syndrome, or TPC, for short.

In TPC, which also runs in families, infants are born with "a tightening of the muscles in the hands, feet, and jaw," Dr. Basson explained. "None of these muscles move right. In the jaw they can't open the mouth fully; in the feet and in the hands they can't bend fully."

Why do heart tumors and TPC appear so often in the same patients? To find out, Basson's team used hi-tech gene analysis techniques to zero in on the genetic mutation responsible for both.

" We found that there's a change in one particular amino acid in a gene for a muscle protein called perinatal myosin," Dr. Basson said.

The myosin proteins play key roles in the contraction-expansion dynamic that allows muscles to work the way they do. The genetic mutation responsible for TPC appears to undermine myosin's role in normal muscle growth in the developing fetus. Genetic mutations in other myosins cause abnormalities in skeletal muscles as well as a potentially lethal heart disorder, hypertrophic cardiomyopathy.

More puzzling, Dr. Basson said, was the question of how a mutation governing a muscle protein encourages heart tumors.

"No one has ever suspected that changes in muscle myosin could be involved in tumor formation," he said. "It is possible that they promote survival of embryonic cells that are still able to divide within the adult heart."

It's this theory that has Dr. Basson and his colleagues most excited.

"A debate has raged recently as to existence of stem cells in the heart," he explained. "If they are there, then in cardiac myxomas, we may be seeing the survival of heart embryonic stem cells into adulthood, and these cells may carry this abnormal myosin into adult life."

This means that, besides identifying the genetic causes of two serious inherited conditions, the study may provide evidence of "cells competent to divide within the adult heart," Dr. Basson said.

"In heart myxomas, these cells are dividing to make a tumor, of course. But imagine if we could control that growth — growing new heart cells. If there are already stem cells resident in the heart, and if you could manipulate those stem cells, you wouldn't have to give someone stem cells from elsewhere. And you wouldn't have to worry about transplanting stem cells into the patient's heart — they're already there."

In the near future, the findings have practical implications for patients with TPC. Because TPC and some cardiac myxomas share the same genetic origin, "we have to recommend now that anybody who has this contracture syndrome should be considered at risk for developing a heart tumor, and they should get surveillance echocardiography on an annual basis," Dr. Basson said.

Pinpointing the gene responsible for TPC also raises hopes for early diagnosis and treatment of the condition — including, perhaps, gene therapy at some point in the future.

Dr. Basson stressed that his theory into myosin's links to possible stem cell activity in the heart remains just that — a theory — and more work needs to be done.

But myosin's role in heart tumor development "does shed a whole new light on what this protein does," he said. "It might help regulate, somehow, cell survival and cell growth in the heart. That's not something we ever expected."

Dr. Basson's work on the study was funded by a grant from the National Institutes of Health. Study co-authors included Dr. Mark Veugelers, Michael Bressan, and Deborah A. McDermott, all of Weill Cornell Medical College, New York; Dr. Stanislawa Weremowicz and Dr. Cynthia C. Morton, Brigham and Women's Hospital, Boston; Dr. C. Charlton Mabry, of the University of Kentucky College of Medicine, Lexington; Dr. Jean-Francois Lefaivre, University of South Carolina School of Medicine, Columbia; Dr. Alan Zunamon, Evanston Northwestern Healthcare, Evanston, Ill.; Dr. Anne Destree, Insititut de Pathologie et de Genetique, Loverval, Belgium; and Dr. Jean-Marie Chaudron, Jolimont Hospital, Jolimont, Belgium.