年龄和组织类型对X连锁Alport综合征女性患者X染色体失活方式的影响

Effects of age and tissue types on X-inactivation patterns in females with X-linked Alport syndrome

目的探讨不同年龄和组织类型对X连锁Alport综合征(XLAS)女性患者X染色体失活方式的影响。方法纳入1997年1月至2006年12月北京大学第一医院(我院)儿科肾脏病遗传门诊就诊符合XLAS诊断标准的家系。根据年龄,将XLAS家系中女性患者分为两组,年龄≤30岁为A组,年龄>30岁为B组。采集患者及其家属静脉血3mL,盐析法提取淋巴细胞基因组DNA。对家系中的女性患者在前臂下1/3处进行皮肤活检,并进行成纤维细胞培养。通过PCR扩增雄性激素受体(AR)基因第一外显子CAG重复序列的多肽性分析X染色体失活。每一标本X染色体失活分析均检测2次,取其平均值用于两组X染色体失活的差异分析,以X染色体失活率≥80%作为X染色体失活倾斜的标准。结果研究期间我院儿科肾脏病遗传门诊共诊断XLAS家系186个,符合纳入和排除标准的XLAS家系共32个,包括36例女性患者,32例男性患者。A组和B组分别为13和23例,平均年龄分别为(17.9±11.7)和(38.6±6.2)岁。①36例女性患者中,外周血中AR基因位点杂合者32例,异质性为88.9%;AR基因位点纯合者4例。外周血中X染色体失活倾斜比例为12.5%(4/32例),其中A组0例,B组4/20例(20.0%),两组差异无统计学意义(χ2=2.743,P=0.098)。②12例女性患者同时分析外周血和皮肤成纤维细胞X染色体失活,结果显示两种组织中X染色体失活方式明显不同,3例患者仅皮肤成纤维细胞显示为X染色体失活倾斜而外周血无失活倾斜;1例外周血显示X染色体失活倾斜而皮肤成纤维细胞无失活倾斜。7/12例(58.3%)患者两种组织中以同一条X染色体失活为主;5/12例(41.7%)患者则相反,两种组织间X染色体失活明显不同。结论不同组织类型而不是年龄可影响XLAS女性患者的X染色体失活方式,这可能是有关XLAS女性患者和X染色体失活研究结果不一致的一个主要原因。

Objective Alport syndrome（AS） is a progressive renal disease characterized by hematuria and progressive renal failure. X-linked AS （XLAS） is the major inheritance form caused by COL4A5 gene mutations. X-inactivation has been suspected to be one of the responsible reasons for this phenomenon, but so far definite correlation is not demonstrated. It is supposed that X-inactivation patterns may vary both with age and tissue types within an individual. This study was to explore the effect of age and tissue types on X-inactivation patterns in XLAS females. Methods Females with XLAS were enrolled to compare the X-inactivation ratios between two groups（age≤30 years as group A and age30 as group B）. X-inactivation ratios were analyzed in cultured skin fibroblasts at the same time to compare the X-inactivation ratios between two tissues using HpaII predigestion of DNA followed by polymerase chain reaction （PCR） of the highly polymorphic CAG repeat of the androgen receptor （AR） gene. Results A total of 36 female cases of XLAS were divided into two groups, group A included 13 patients aged under or equal to 30 years and group B included 23 patients aged over 30 years. One patient in group A and 3 patients in group B were uninformative for the X-inactivation assay used, the rate of heterozygosity at the AR locus of the 36 female patients was 88.9%. Only 12.5%（4/32） females detected showed skewed X-inactivation in peripheral blood cells. No（0/12） individual under 30 years of age had skewed X-inactivation while 20%（4/20） individuals over 30 years of age had skewed X-inactivation in peripheral blood cells （P0.05）. The X-inactivation patterns of the 12 patients showed marked variation between blood cells and skin fibroblasts. Seven of 12 patients（58.3%） had similar X-inactivation ratios in both tissues, but the other 5 patients（41.7%） had the opposite X-inactivation patterns in both tissues. Conclusions Different tissue types instead of age may affect the X-inactivation patterns in XLAS females, this may explain the contradictory results between X-inactivation and the variable phenotype of XLAS females.