Genetic Polymorphisms Associated with Priapism in Sickle Cell Disease.

Priapism, a painful and prolonged erection, has been reported to occur in 30–45% of male patients with sickle cell disease (SCD). However, little is known about the pathological processes and genetic risk factors that contribute to the occurrence of priapism. The identification of genetic variables that are associated with priapism may therefore help define both critical pathophysiologic mechanisms not otherwise apparent, as well as patients at increased risk. We examined genetic variation in our sample of 199 unrelated, adult (>18 years), male patients with Hb SS and Hb Sβ⁰-thalassemia, 83 (42%) of whom reported a history of priapism. Candidate genes for association with priapism were identified based on their involvement in adhesion, coagulation, inflammation, and cell signaling. Additionally, we examined genes involved in NO biology (NOS2, NOS3, SOD1, SLC4A1). Finally, we also examined polymorphisms in the KLOTHO gene, which has previously been associated with priapism. We examined a total of 389 SNPs in 48 candidate genes. Except for the gene encoding the β2 adrenergic receptor, SNP genotyping was performed by TaqMan, using Assays-on-Demand or Assays-by-Design genotyping products (Applied Biosystems). Allele tests were used to detect genetic associations with priapism. Strong evidence of association was found for SNP rs7526590 in the transforming growth factor-β receptor, type III (TGFBR3) gene (p=.00058), SNP rs10244884 in the aquaporin (AQP1) gene (p=.00068), and SNP rs3768780 in the integrin αV (ITGAV) gene (p=0.00090). A second ITGAV SNP (rs3768778), in linkage disequilibrium (r²=.59) with the first, also showed association with priapism (p=.00888). The A1 subunit of coagulation factor XIII (F13A1) had four SNPs (hcv1860621, rs1032045, rs1674074, rs381061) with p-values less than 0.010 (p-values = 0.00156, 0.00415, 0.00648, and 0.00712, respectively). The linkage disequilibrium among these F13A1 SNPs is negligible (r² <.15). We also adjusted for multiple testing using the Benjamini-Hochberg procedure (significance threshold <.10). SNP rs7526590 in TGFBR3, SNP rs10244884 in AQP1 and SNP rs3768780 in ITGAV each had a false discovery rate (FDR) p-value of .09834. SNP rs1674074 in F13A1 had an FDR p-value of .12733. The other SNPs in F13A1 had large FDR p-values, close to .30. We did not detect an association between priapism and genetic variation in the Klotho gene, as was previously reported by Nolan et al. (2005). Specifically, SNPs rs2249358, rs211234 and rs211239 showed a virtually identical distribution of genotypes for individuals with and without a history of priapism. However, our population is not identical to the previous study, which included patients as young as 10 years old. In conclusion, our data support the hypothesis that genetic variation is associated with risk for priapism among males with SCD and suggest that genes involved in the TGFβ pathway, coagulation, cell adhesion and cell hydration pathways may be important.

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