Four-fold Rise in CMT Cases Seen in Denmark from 1988 to 2012, Study Reports

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by Alice Melao |

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Researchers report finding a more than four-fold increase in the prevalence of Charcot-Marie-Tooth disease in Denmark between 1988 and 2012, possibly because of better disease diagnosis. They also report significantly higher mortality rates among CMT patients compared to the general public than is thought to exist.

Conducted by a team at Aarhus University Hospital, the study is titled “Charcot-Marie-Tooth disease in Denmark: a nationwide register-based study of mortality, prevalence and incidence” and appeared at the journal BMJ Open.

CMT is a common neurological disorder, and more than 80 genes are identified as involved in its development. Despite advances in understanding this disease and its natural development, little is known about its epidemiology, or its distribution and rates across a population.

This disease is characterized by slowly progressive muscle weakness, deformities of the feet and hands, and loss of tendons reflexes. But its symptoms and progression can vary widely, even among patients in the same family — making  CMT a challenge both to diagnose in individuals and to detect broader patterns within countries.

To conducted a nationwide analysis of CMT incidence, prevalence, and mortality rates, the Danish team used data from the Danish National Patients Registry (DNPR). The registry  is a confirmed and valid source of CMT diagnostic records.

The study included all DNPR records of CMT primary diagnosis at a hospital between 1977 and 2012. A total of 1,534 patients, 882 men and 652 women, were included in the study. People were diagnosed at age 42.5 on average, and their average age at death was 70.

Analysis of disease incidence between 1988 and 2012 revealed a  four-fold increase, with CMT found to affect 22.5 in every 100,000 people in Denmark in 2012. But the researchers think even this finding is an underestimation, because CMT is frequently misdiagnosed or patients are not recorded.

Technical advances in diagnosing disease like CMT during the study period, such as availability of faster and accurate genetic testing, likely contributed to the reported increase in disease incidence.

“In 1992 the first genetic analysis for CMT became available to clinicians, and since then the number of genes available for analysis, as well as the general awareness of hereditary disorders, has increased steadily,” they wrote.

But, “patients with milder signs and symptoms, or patients to whom CMT is already a well-known part of their family history, might never be referred to a hospital department” and therefore not part of the database used, they added.

A total of 295 deaths were reported during this 24-year period, representing an increase in mortality rates of 36% compared to the general population.

The disease was also seen to be significantly more prevalent in men than in women, and less prevalent in those age 29 or younger.

“Until now, it has been generally assumed that the lifespan of patients with CMT was unaffected. However, our study of a large group of patients diagnosed with CMT reveals a significant increase in mortality,” the study states. “This finding brings to light a new set of intriguing questions and areas for further research to what causes this increase in mortality.”

Further understanding here can also help to steer research and public health resources to areas that could best benefit CMT patients, the researchers concluded.