IN-VITRO AND RAPID IN-SITU TRANSGLUTAMINASE ASSAYS FOR CONGENITAL ICHTHYOSES - A COMPARATIVE-STUDY

Autosomal recessive congenital ichthyoses are a heterogeneous group of disfiguring skin diseases. They are generally characterized by variab le scaling and erythroderma, and patients are frequently collodion bab ies at birth. Autosomal recessive congenital ichthyoses are represente d in 25 of our 50 families by a defective keratinocyte transglutaminas e (TGK). Pathogenic classification is difficult to assess on clinical grounds for autosomal recessive congenital ichthyoses and impossible f or collodion babies. Thus, we have established a rapid TGK assay in si tu on frozen skin sections using incorporation of dansyl-cadaverin to assess transglutaminase (TG) activity in combination with immunohistoc hemistry for TGK protein. Results were compared with TG activity level s measured in cultured differentiating keratinocytes. Sixteen of 26 pa tients, including a collodion baby, had strongly diminished TG activit y in the cell periphery of differentiating keratinocytes and membrane- bound TG activities in vitro, ranging from 2.2 to 281.3 pmol per h mg. Nine of 26 patients, including a collodion baby, showed strong TG act ivity in the cell periphery of differentiating keratinocytes in situ a nd membrane-bound TG activities in vitro ranged front 1519 to 10917 pm ol per h mg. In one case, TG assay in situ was ambiguous; however, mem branous TG activity in vitro was very low at 76.9 pmol/h X mg. Our res ults demonstrate an excellent correlation of TG assays in vitro and in situ. In addition, we present a novel test with prognostic value for the collodion baby phenotype. This assay allows rapid pathogenic class ification of autosomal recessive congenital ichthyoses with only one c aveat that ill rare ambiguous cases it might be necessary for groper c lassification to assess membrane-bound TG activity in vitro.