Frequency of enzyme deficiency variants in erythrocytes of newborn infants.

The frequency of enzyme deficiency variants, defined as alleles whose products are either absent or almost devoid of normal activity in erythrocytes, was determined for nine erythrocyte enzymes in some 675 newborn infants and in approximately 200 adults. Examples of this type of genetic abnormality, which in the homozygous condition are often associated with significant health consequences, were detected for seven of the nine enzymes studied. Fifteen inherited enzyme deficiency variants in 6142 determinations from the newborn population and 5 variants in 1809 determinations from adults were identified. Seven of the deficiency variants involved triosephosphate isomerase, a frequency of 0.01 in the newborn population. The average frequency of 2.4/1000 is 2-3 times the frequency observed for rare electrophoretic variants of erythrocyte enzymes in this same population.