Elevated frequency of carriers for triosephosphate isomerase deficiency in newborn infants

Seven newborns with erythrocyte triosephosphate isomerase (TPI) activity levels consistent with the existence of a "null" allele in heterozygous form were identified among 146 Black infants studied. This allele frequency of 0.024 is ten times the frequency of 0.0024 observed in White newborns (5 heterozygotes/1048 infants). Each carrier infant has one parent with a level of TPI activity expected of a heterozygous deficient (carrier) adult, whereas the other parent has a normal level of TPI activity, as would be expected for an autosomally inherited genetic trait. All probands as well as affected parents, are asymptomatic as anticipated for heterozygotes having 50% of the expected enzymatic activity. The data are consistent with the existence of a "null" allele, designated TPI 1 degree, at the structural locus for TPI, although no immunologic or direct evidence of inactive or altered subunits was obtained. This high allele frequency implies one of every 2000 Black newborns should be homozygous deficient; this is in conflict with the low number of homozygous deficient afflicted individuals which have been actually identified to date.