Valle and his colleagues next scored each gene in these four major categories based on the clinical features of the diseaseincluding age of onset, mode of inheritance, frequency, severity, extent of tissue involvement and association with malformations.

The analysis yielded a number of striking general insights, said Valle. For example, the scientists found that genes that encoded transcription factors are over-represented among genes that cause malformation diseases that begin in utero. This frequency, said Valle, reflects the importance of transcription factors in embryonic development.

The analyses also indicated that "an extraordinarily high" fraction of diseases with onset in the first year of life are caused by defects in genes that encode enzymes. Such a finding is expected, wrote the scientists, because the mothers metabolic system protects the fetus from enzyme deficiencies until birth. Metabolic deficiencies are usually identified after birth.

The scientists found that diseases caused by genes that encode enzymes are primarily recessive, while those caused by genes whose proteins influence other proteins are evenly split between dominant and recessive. Also, diseases caused by transcription factors are more likely to be dominant, found the researchers.

Each of the four major functional categories of gene showed a different peak age of onset, found the scientists. Diseases due to transcription factors peaked in utero; those due to enzymes in the first year; those for receptors between one year and puberty, and those due to protein modifiers in early adulthood.

"These insights represent only the beginning of the kinds of discoveries of general principles that can be made as a comprehensive list of disease genes is developed and compared to the list of all human genes," said Valle. "Clearly, the human genome projects will enable us to make this
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
11-Feb-2001