Abstract: Objective To explore the possible correlation between the genetic variations of the melanocortin receptors (MCRs, including MC2R, MC3R and MC4R) and adrenocorticotropic hormone (ACTH) responsiveness in patients with infantile spasms, and to investigate the function of single nucleotide polymorphism (SNP) found in this study. Methods Direct sequencing method was used to test variations and polymorphisms in the promoter and coding regions of the MC2R, MC3R and MC4R gene. Haplotypes were structured by using SHEsis and Haploview3.32 programs to analyze the distribution frequencies of polymorphism genotypes, alleles and structured haplotypes in Chinese patients with infantile spasms and normal controls. The association between ACTH responsiveness and genetic variations was also assessed. Results Four SNPs were identified in the MC2R promoter region, one of which was new -found locus named-2T > C. Three SNPs (rs1893220, rs2186944 and -2T > C) showed a significant difference between the cases and controls (P = 0.04, 0.02, 0.01). The common haplotype TCCT may give protection against the development of infantile spasms (P = 0.00). Besides, TCCT carriers were more sensitive to ACTH therapy than non-carriers (P = 0.00). The in vitro study proved that the translational efficiency of TCCT promoter in MC2R gene was four times higher than that of TCCC promoter (P = 0.00). MC2R expression assay showed a 5-fold increase in the TCCT promoter in presence of ACTH, compared with that in absence of ACTH (P = 0.00). However, responsiveness to ACTH in expression by TCCC promoter showed only 1.50-fold increase after ACTH stimulation (P > 0.05). The SNP rs11872992 in MC4R gene was related to the development of infantile spasms, as the efficiency of TC genotype in cases was lower than that of normal controls (P = 0.00). The ACTH therapy results of T-allele-carriers were better than that of non-T-allele-carriers (P = 0.01). The difference of SNP distribution frequencies in MC3R gene was not statistically significant (P > 0.05). Conclusion The study revealed an association between polymorphism in MCRs (MC2R and MC4R) promoter and the development of infantile spasms, and ACTH responsiveness in patients with infantile spasms. These findings may provide a clue for clinicians to find an early predictive marker for the responsiveness to ACTH and improve the understanding of pathogenesis in infantile spasms.

Key words: Receptors, melanocortin, Polymorphism, genetic, Genes, Spasms, infantile, Adrenocorticotropic hormone

摘要： 目的  探讨黑皮质素受体（MC2R ~ MC4R）基因变异及单核苷酸多态性与婴儿痉挛症发病及促肾上腺皮质激素治疗反应性的关系，并对研究中发现的最具意义的单核苷酸多态性进行深入的功能学研究。方法  采用DNA 直接测序法检测MC2R ~ MC4R 基因编码区及启动子区基因突变及多态性；SHEsis 和Haploview3.32 程序构建单体型，分析不同多态性基因型、等位基因及所构建单体型在婴儿痉挛症患儿和正常对照受试儿童中的分布频率，并观察其与促肾上腺皮质激素治疗反应的相关性。结果  测序显示，MC2R 基因启动子区共存在4 个单核苷酸多态性位点，其中-2T > C 为新发现位点，3 个单核苷酸多态性位点（rs1893220、rs2186944 和-2T > C）组间分布频率差异具有统计学意义（P = 0.04，0.02，0.01）。常见单体型TCCT 对婴儿痉挛症的发生具有保护作用（P = 0.00），且TCCT 携带者比非携带者对促肾上腺皮质激素治疗更为敏感（P = 0.00）。体外功能学研究证实，MC2R 基因TCCT 型启动子转录效率是TCCC 的4 倍（P = 0.00），经促肾上腺皮质激素刺激后含TCCT 单体型启动子MC2R mRNA 表达水平上调5 倍（P = 0.00），而含TCCC 单体型启动子仅上调1.50 倍（P > 0.05）。MC4R 基因启动子区单核苷酸多态性位点rs11872992 与婴儿痉挛症的发生有关，婴儿痉挛症组患儿TC 型频率低于正常对照组（P =0.00）；T 型等位基因携带者对促肾上腺皮质激素治疗效果优于非T 型等位基因携带者（P = 0.01）。但MC3R 单核苷酸多态性组间分布频率差异无统计学意义（P > 0.05）。结论  黑皮质素受体单核苷酸多态性与婴儿痉挛症的发生有一定关系，并可影响促肾上腺皮质激素治疗的反应性。这一发现有助于理解婴儿痉挛症的发病机制，并为临床早期预测促肾上腺皮质激素治疗反应提供一定线索。

关键词: 受体, 黑皮质素； 多态现象, 遗传； 基因； 痉挛, 婴儿； 促肾上腺皮质激素