Family studies in psoriasis. II. Inheritance of HLA genotypes.

The study of HLA genotypes in psoriatic families attempts to probe into the genetic transmission of disease. A strong association of psoriasis with HLA antigens determined by locus B is well known, but its relationships are still unsolved. A group of 39 families, living in southern Poland and containing 19 affected parents and 52 psoriatic children, was studied. To discriminate between dominant and recessive modes of 'disease' genes inheritance, two tests were used. No significant differences were found between the observed and the expected distributions of genotypes with HLA-B 13 or HLA-B 17. The expected and the observed numbers of affected sib pairs sharing two, one or no HLA haplotypes were compatible with the proportions of 1/4, 1/2 and 1/4 in the case of independent segregation of psoriasis and HLA antigens. The results support the hypothesis of multifactorial determination of disease. The hypothetical inheritance of parental HLA haplotypes carrying 'psoriatic' genes in cis or trans positions was considered. Of nine possible combinations, two were shown graphically that resulted in offspring compatible with the observed pyenotypical expression of disease.