We recently mapped the disease locus for severe autosomal recessive lamellar ichthyosis (LI) to chromosome 14q11 and showed complete linkage with TGM1, the gene encoding transglutaminase 1. We have now identified point mutations in TGM1 in two of the multiplex LI families used in the linkage study. Each nucleotide change causes a non-conservative amino acid substitution of histidine for one of two adjacent arginine residues in exon 3 of the gene (Arg141His, Arg142His). Within the transglutaminase family, these arginines are invariant within a conserved region, distant from the catalytic site of the enzyme. We hypothesize that these mutations adversely affect formation of crosslinks essential in production of cornified cell envelopes and a normal stratum corneum layer of the skin.

Phytohemagglutinin causes cultured lymphocytes to agglutinate, divide, and produce gamma-globulin. Most cells are transformed into large lymphocytes, some resembling plasmocytes. Actinomycin D stops gamma-globulin production after 2 hours. When specific antigens are added to lymphocytes from sensitized individuals, only some cells undergo morphological transformation, produce gamma-globulin, and divide. When cells or cell extracts from an unrelated individual are added to a culture, a similar reaction occurs.

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The frequency of isoniazid slow inactivators is very high among Eqyptians, 82% have more than 0.91 y/ml of free INH in serum specimens obtained six hours after a single dose of 10 mgm/kgm. The incidence of the allele for INH acetylase enzyme deficiency is estimated at 0.9059 and that of the heterozygous carrier of this allele at 0.1705.

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