Harvard Doctors Discover Disease That Produces Mental Retardation

A team of Harvard doctors has discovered a new hereditary disease, caused by an enzyme deficiency, which leads to mental retardation.

Children afflicted with the disease exhibit a built-in aversion to meat and milk products, and often go into a diabetes-like coma after eating these foods.

The cause appears to be the lack of a single enzyme which is supposed to aid in the breakdown of something called isovaleric acid into simpler compounds. If the enzyme is missing, the acid accumulates in the body and a whole chain of chemical reactions is broken.

Drs. Kurt J. Isselbacher, Matthew A. Budd, and Lewis B. Holmes of the Medical School, and Dr. Kay Tanaka, a visiting assistant professor at the Med School from the University of Tokyo, believe that a special low-protein diet may prevent the brain damage

Isovaleric acid is produced from auamino acid called leucine which is found in many proteins. If most of the protein can be removed from the diet the problem of the blocked chemical chain can be indirectly solved by eliminating the chain entirely.

Thousands of chemical reactions in the body require the aid of enzymes, and the breakdown of any one of them could lead to a disease like this. There are about 30 such conditions now on record, according to Isselbacher.

Damage From Broken Chain

There are many ways in which the broken chemical chain can lead to brain damage. If the reaction "A goes to B" breaks down, the brain may be affected by the accumulation of A in the bloodstream, or the lack of B, or by some chemical which is produced by the surfeit of A. It is believed that in this particular case, the acid itself causes brain damage.

The disease has been studied in two children, now five and three years old, at the Massachusetts General Hospital. They were first brought in two years ago, but these four doctors became involved in the case last summer.

The clue which led to the understanding of the disease was an odor quite similar to the odor of cheese or sweaty feet which accompanied the attacks in the children. Chemical tests led to the identification of isovaleric acid, in doses up to 100 times normal.

At least two more cases that seem to be the same disease have been found, and others are expected to turn up now that scientists know what to look for.

The four researchers prepared a paper on their work which Dr. Tanaka deliverd to the Federation of American Societies for Experimental Biology in Atlantic City, N.J. on Saturday.