( Studying mutations that give rise to a ...)Gene found for rare disorder may reveal new pathway in mental retardation

An international team of researchers identified two genes that contribute to Cornelia deLange syndrome (CdLS), a multisystem genetic disease that affects an estimated one in 10,000 children. The disease varies from milder to more severe forms, but classically includes mental retardation, impaired growth, heart defects, feeding problems, deformed upper limbs and distinctive facial features.

In the current study, mutations in two genes of interest cause mental retardation, but with less pronounced facial features and none of the limb defects, such as missing hands or fingers, that are hallmarks of classical cases of CdLS. The genes play important roles in early development, and when mutated, cause brain abnormalities.

"Our work suggests that a subset of patients with mental retardation may have mutations in these genes, without showing the broader range of symptoms identified in diseases such as Cornelia deLange syndrome," said study leader Ian D. Krantz, M.D., a specialist in pediatric genetics at The Children's Hospital of Philadelphia. Dr. Krantz and his co-author, Laird S. Jackson, M.D., of Drexel University College of Medicine, led the study team that announced the discovery of NIPBL, the first gene known to cause CdLS, in 2004.

The current study appeared online Jan. 17 in the American Journal of Human Genetics, in advance of print publication in March 2007.

In contrast to the NIPBL gene, in which mutations cause roughly half of known CdLS cases, the researchers found that mutations in the new genes, SMC3 and SMC1A, cause only about 5 percent of CdLS cases. All three genes produce proteins called cohesin proteins. Cohesin proteins have long been known to play an important role in many
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Source:Children's Hospital of Philadelphia