This study was approved by the National Defense Medical College’s institutional ethics committee, and all procedures were performed in accordance with the Declaration of Helsinki. Written informed consent was obtained from each subject participating in this study before DNA samples and erythrocyte protoporphyrin data were collected.
The study participants comprised 23 Japanese patients (13 males and 10 females) with suspected photosensitivity based on their clinical histories and/or symptoms. Mean age (years) and standard deviation were 55.5 ± 20.1. Patients with systemic, metabolic, or genetic disorders, including porphyria, xeroderma pigmentosum, and systemic lupus erythematosus, were excluded. Those with drug-induced photosensitivity and photocontact dermatitis were also excluded. We performed phototests with UVB (280–380 nm) and UVA (300–430 nm) lamps of Dermaray-200 (Toshiba Medical Supply, Tokyo, Japan). Seven patients were diagnosed with CAD based on the criteria of reduced MED to UVB (50 mJ/cm2) and/or UVA (10 J/cm2). Five CAD patients showed photosensitivity to both UVB and UVA; one CAD patient showed photosensitivity to UVA alone, and another CAD patient showed photosensitivity to UVB alone. The remaining 16 patients exhibited normal reactions to UVB and UVA on phototesting, but had histories of recurrent erythema/papules on sun-exposed areas; therefore, they were grouped as non-CAD patients.
Genomic DNA was extracted from whole peripheral blood cells. Genotyping of two ABCG2 dysfunctional variants, p.Q126X (c.376C > T) and p.Q141K (c.421C > A), was performed using the TaqMan method (Thermo Fisher Scientific, Waltham, MA, USA) with a LightCycler 480 (Roche Diagnostics, Mannheim, Germany), as previously described . Custom TaqMan assay probes were designed as follows. For p.Q126X, VIC-CCACTAATACTTACTTGTACCAC and FAM-CCACTAATACTTACTTATACCAC; for p.Q141K, VIC-CTGCTGAGAACTGTAAGTT and FAM-CTGCTGAGAACTTTAAGTT. To confirm their genotypes, DNA sequencing analysis was performed with the following primers. For p.Q126X, forward 5′-TGTACAATGAAAAGAGAAAGGTGAG-3′ and reverse 5′-CTGCCTTTTCACATAAGTGTC-3′; for p.Q141K, forward 5′-ATGGAGTTAACTGTCAT TTGC-3′ and reverse 5′-CACGTTCATATTATGTAACAAGCC-3′. Direct sequencing was performed with a 3130xl Genetic Analyzer (Thermo Fisher Scientific).
R software (version 3.1.1: http://www.r-project.org/) was used for all the statistical analysis calculations. Linear regression analysis and the Cochran–Armitage test were performed for the association analyses. The P value of the Hardy–Weinberg equilibrium was calculated using the Chi-square test with Yates’ correction. We set the significance threshold to α = 0.05.