Inherited variations in human phosphohexose isomerase

SUMMARY 1. The elctrophoretic pattern of phosphohexose isomerase has been examine in the blood of 3397 unrelated individuals from several different populations groups. 2. Eight variant phenotypes were identinfied and these were designated PHI 2‐1, 3‐1, 4‐1, 5‐11 6‐1, 7‐1, 8‐1, 9‐1. All of these were rare in the populations studied except the variant designated PHI 3‐1, which was observed with a frequency of about 1% in a mixed population of Asiatic Indians. 3. Studies of selected families indicated that the variants occured in individuals who are heterozygous for one or another of a series of rare alleles at an autosomal locus. 4. Studies on the family of a patient that the patient was heterozygous for two different rare alleles at the PHI locus, each associated with reduced PHI activity. The patinet's mother showed the PHI 9‐1 phenotype and his father showed a new phenotype designated PHI 10‐1. The patient's phenotype has been designeated PHI 9‐10. 5. The enzyme appears to be a dimer and in heterozygotes isozymes of hybrid submit compostion as well as isozymes of like subunit compostion are apparently formed.