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A new genetic test may help identify persons at risk for inheriting Huntington's disease, a disease whose effects show in adults and which is characterized by progressive mental deterioration, jerky movements (chorea), and clumsiness. The new test involves analyzing the number of CAG trinucleotide repeats in a gene on the chromosome that mutates and creates Huntington's disease. Ninety-nine per cent of the 1,007 persons studied with a diagnosis of Huntington's disease had expanded CAG repeats. CAG results of persons with other neuropsychiatric disorders were compared to the Huntington's group. These individuals did not exhibit expanded CAG repeats. Previously, the main test to prove whether a person had inherited the mutant gene for Huntington's disease was to obtain DNA samples from key relatives. The new test is more accurate than the DNA tests, and helps maintain the privacy of the individual being tested.

Multiple endocrine neoplasia type 2A (MEN 2A) is a prevalent cancer syndrome affecting the neural ectodermal derived tissues. Medullary Thyroid Carcinoma (MTC) and phaeochromocytoma are characteristic of the MEN 2A. At lower levels of the human thyroid and in MTC and phaeochromocytoma, a receptor tyrosine kinase gene, the RET photo-oncogene, is invested in the DNA segment. A recent study identified 20 RET proto-oncogene missense mutations from 23 apparently distinct MEN 2A families, but not in 23 normal controls. Of the 20 mutations, 19 affect similar conserved cysteine residue of the RET extracellular and transmembrane domains at the boundary.