CHICAGO (Reuters) - International teams of researchers using advanced gene sequencing technology have uncovered a single genetic mutation responsible for a rare brain disorder that may have stricken families in Turkey for some 400 years.

The discovery of this genetic disorder, reported in two papers in the journal Cell, demonstrates the growing power of new tools to uncover the causes of diseases that previously stumped doctors.

Besides bringing relief to affected families, who can now go through prenatal genetic testing in order to have children without the disorder, the discovery helps lend insight into more common neurodegenerative disorders, such as ALS, also known as Lou Gehrig's disease, the researchers said.

The reports come from two independent teams of scientists, one led by researchers at Baylor College of Medicine and the Austrian Academy of Sciences, and the other by Yale University, the University of California, San Diego, and the Academic Medical Center in the Netherlands.

Both focused on families in Eastern Turkey where marriage between close relatives, such as first cousins, is common. Geneticists call these consanguineous marriages.

In this population, the researchers focused specifically on families whose children had unexplained neurological disorders that likely resulted from genetic defects.

Both teams identified a new neurological disorder arising from a single genetic variant called CLP1. Children born with this disorder inherit two defective copies of this gene, which plays a critical role in the health of nerve cells.

Babies with the disorder have small and malformed brains, they develop progressive muscle weakness, they do not speak and they are increasingly prone to seizures.

Dr Ender Karaca, a post-doctoral associate in the department of molecular and human genetics at Baylor, first encountered the disorder in 2006 and 2007 during his residency training as a clinical geneticist in Turkey.

"We followed them for years," said Karaca, a lead author on one of the papers. Karaca said he and his colleagues performed some basic genetic tests on the families but to no avail.

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Researchers discover that two defective copies of a single gene cause rare brain disorder