A nonsynonymous substitution of cystatin A, a cysteine protease inhibitor of house dust mite protease, leads to decreased mRNA stability and shows a significant association with atopic dermatitis.

Background: Cystatin A (CSTA) is a strong candidate for atopic dermatitis (AD) because it maps to AD susceptibility locus on chromosome 3q21 and it does inhibit Der p 1 and Der f 1, major house dust mite cysteine proteases and environmental triggers for AD and asthma.
Objective: To examine any association between polymorphisms in CSTA and AD and study the effect on the CSTA mRNA expression level.
Methods: We identified three polymorphisms and characterized the linkage disequilibrium mapping of the CSTA gene. All three CSTA polymorphisms were genotyped in 100 AD patients and 203 matched controls. Subsequently, we performed transfection-based RNA stability assays.
Results: We found a significant association between the CSTA +344C variant and AD [odds ratio (OR) = 1.91; P = 0.024]. When further 61 control samples were genotyped. The association with CSTA +344C allele was enhanced OR = 2.13; P = 0.006. To test whether the CSTA +344 affected the CSTA transcriptional activity, the decay rates of RNAs transcribed from the CSTA +344C and CSTA +344T variants were investigated. COS-7 cells were transfected with a pcDNA3.1-CSTA+344C or a pcDNA3.1-CSTA+344T construct and cultured in the presence or absence of actinomycin D. Real-time RT-PCR revealed that CSTA +344C mRNA is more than two times less stable than the CSTA +344T mRNA (P < 0.001).
Conclusion: These results suggest that the CSTA +344C allele associated with unstable mRNA could result in failing to protect the skin barrier in AD patients from both exogenous and endogenous proteases.