New Cause of Inherited Low Thyroid Disorder Found

[~MaryO~]

http://story.news.yahoo.com/news?tm....es_dc_1

 

New Cause of Inherited Low Thyroid Disorder Found

Thu Jul 11, 9:28 AM ET

By Alison McCook

 

NEW YORK (Reuters Health) - Changes in one gene involved in the synthesis of thyroid hormone may explain some cases of inherited hypothyroidism, or abnormally low levels of thyroid hormone, Dutch researchers report.

 

 

The investigators found that a child with a severe thyroid hormone deficiency had inherited mutated forms of both copies of a gene called thyroid oxidase 2 (THOX2), which is involved in the process of producing thyroid hormone. Furthermore, three of eight patients with milder, temporary forms of the condition carried one mutated and one normal copy of THOX2.

 

"We have found a new cause of congenital hypothyroidism," lead author Dr. Jose C. Moreno of the University of Amsterdam in the Netherlands told Reuters Health.

 

The thyroid is a gland in the neck that regulates heart rate, metabolism, growth, mental function, energy and mood. During the first months of life, babies need a lot of thyroid hormone to help their brain develop and mature. However, after around 6 months, the need for thyroid hormone drops significantly, and falls to normal, adult levels a few years later.

 

Hypothyroidism, the most common form of inherited endocrine disorder, is diagnosed in 1 of every 3,000 to 4,000 babies. The condition is treated by administering extra doses of thyroid hormone.

 

In some patients born with permanent or temporary hypothyroidism, doctors can pinpoint the cause of the disorder, but in many cases, there is no clear explanation.

 

In the present study, published in the July 11th issue of The New England Journal of Medicine ( news - web sites), Moreno and his team performed DNA analysis on nine patients with unexplained congenital hypothyroidism and their relatives.

 

The researchers found that four of the nine patients carried mutations in the THOX2 gene that affect the functioning of the protein it encoded.

 

However, in the five remaining patients, all of whom carried the mild, transient form of the disease, the investigators did not identify any genetic links to their condition. In an interview with Reuters Health, Moreno said that this lack of finding does not mean no genetic link exists.

 

"It might be that these five kids have mutations in genes that have not yet been discovered," he suggested.

 

One striking aspect of these results is that even a temporary form of hypothyroidism can have a genetic basis, Moreno added. Having only one good copy of THOX2 means patients produce lower than needed amounts of thyroid hormone, a problem that seems to disappear later in life once the patient's need for thyroid hormone decreases.

 

However, the genetic defect that caused the condition never disappears, and some patients may experience a resurgence in symptoms at some point during adulthood, such as during pregnancy, when mothers need more thyroid hormone to feed the brain of the developing fetus, Moreno noted.

 

Currently, children diagnosed with hypothyroidism are given thyroid hormone for many years. However, if they have only one mutated copy of THOX2, their need for extra hormone may significantly decrease earlier in life. These results may help identify those infants who will no longer need extra doses of the drug after the first several months of life, Moreno said.

 

And, of course, researchers may one day be able to correct the genetic defect that is causing the condition. "Gene therapy--replacing defective copies of genes by normal genes--remains a possibility in the long-term perspective," Moreno noted.

 

SOURCE: The New England Journal of Medicine 2002;347:95-102.