Keratins as susceptibility genes for end-stage liver disease

Keratins 8 and 18 protect the liver from stress. Keratin 8 and 18 variants in 17 of 467 liver disease explants and 2 of 349 blood bank controls were previously reported in 5 analyzed exonic regions. We asked whether mutations were present in the remaining 10 exons of keratins 8 and 18.

Exonic regions were polymerase chain reaction-amplified from genomic DNA, isolated from the above-mentioned 2 cohorts, and analyzed for the presence of mutations. Mutant keratins were also studied biochemically.

We identified 10 novel keratin 8 and 18 heterozygous variants in 44 of 467 explants and 11 of 349 controls: keratin 18 deletion (delta64-71), a keratin 8 frameshift that truncates the last 14 amino acids; 8 missense keratin 8 and 18 alterations; and several new polymorphisms. The most common variant, keratin 8 R340H, at the highly conserved R340 was found in 30 of 467 explants and 10 of 349 controls (P = .02) and was confirmed in the diseased livers by generation of an R340H-specific antibody. Germline transmission and variant protein expression were verified. The mutations involved a variety of liver diseases, and some variants had an ethnic background preponderance. Mutations that introduced disulfide bonds (keratin 8 G61C or R453C) decreased keratin solubility, particularly after oxidative stress, whereas others decreased keratin 8 phosphorylation (keratin 8 G433S).

The overall frequency of keratin 8 and 18 variants was 12.4% in 467 liver disease explants and 3.7% in 349 blood bank controls (P < .0001). Variants can alter keratin solubility or phosphorylation and may render individuals susceptible to end-stage liver disease, depending on their genetic background and exposure to other insults, such as alcohol or viral infection.