The article by Lo et al1 in this issue, describing a late clinical presentation in a patient with partial carbamyl phosphate synthetase I deficiency, highlights a common diagnostic pitfall. The usual thinking of the medical community is that genetic diseases are so rare that we are not going to see them, and when we do see them there is nothing we can do about them. Both of these misconceptions turn out to be wrong.
As many as 5% of newborns will express a significant genetic disorder during infancy and childhood, and at least a similar if not larger percentage may express a genetic disorder at a somewhat later stage of life.
The group of inborn errors of metabolism (errors of the urea cycle, amino acid metabolism, and organic acid metabolism) represents one of the better examples for the two major concepts of human genetics—heterogeneity and