Origin of the polymorphism of the involucrin gene in Asians

The involucrin gene, encoding a protein of the terminally differentiated keratinocyte, is polymorphic in the human. There is polymorphism of marker nucleotides a two positions in the coding region, and there are over eight polymorphic forms based on the number and kind of 10-codon tandem repeats in that part of the coding region most recently added in the human lineage. The involucrin alleles of Caucasians and Africans differ in both nucleotides and repeat patterns. We show that the involucrin alleles of East Asians (Chinese and Japanese) can be divided into two populations according to whether they possess the two marker nucleotides typical of Africans or Caucasians. The Asian population bearing Caucasian-type marker nucleotides has repeat patterns similar to those of Caucasians, whereas Asians bearing African-type marker nucleotides have repeat patterns that resemble those of Africans more than those of Caucasians. The existence of two populations of East Asian involucrin alleles gives support for the existence of a Eurasian stem lineage from which Caucasians and a part of the Asian population originated.