Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, China.
Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China.
CNS Neurosci Ther. 2023 Dec;29(12):4059-4069. doi: 10.1111/cns.14329. Epub 2023 Jun 28.
Christianson syndrome (CS) is caused by mutations in SLC9A6 and is characterized by global developmental delay, epilepsy, hyperkinesis, ataxia, microcephaly, and behavioral disorder. However, the molecular mechanism by which these SLC9A6 mutations cause CS in humans is not entirely understood, and there is no objective method to determine the pathogenicity of single SLC9A6 variants.
Trio-based whole exome sequencing (WES) was carried out on two individuals with suspicion of CS. qRT-PCR, western blot analysis, filipin staining, lysosomal enzymatic assays, and electron microscopy examination, using EBV-LCLs established from the two patients, were performed.
Trio-based WES identified a hemizygous SLC9A6 c.1560dupT, p.T521Yfs23 variant in proband 1 and a hemizygous SLC9A6 c.608delA, p.H203Lfs10 variant in proband 2. Both children exhibited typical phenotypes associated with CS. Expression analysis in EBV-LCLs derived from the two patients showed a significant decrease in mRNA levels and no detectable normal NHE6 protein. EBV-LCLs showed a statistically significant increase in unesterified cholesterol in patient 1, but only non-significant increase in patient 2 when stained with filipin. Activities of lysosomal enzymes (β-hexosaminidase A, β-hexosaminidase A + B, β-galactosidase, galactocerebrosidase, arylsulfatase A) of EBV-LCLs did not significantly differ between the two patients and six controls. Importantly, by electron microscopy we detected an accumulation of lamellated membrane structures, deformed mitochondria, and lipid droplets in the patients' EBV-LCLs.
The SLC9A6 p.T521Yfs23 and p.H203Lfs10 variants in our patients result in loss of NHE6. Alterations of mitochondria and lipid metabolism may play a role in the pathogenesis of CS. Moreover, the combination of filipin staining with electron microscopy examination of patient lymphoblastoid cells can serve as a useful complementary diagnostic method for CS.
克里斯蒂安森综合征（CS）是由 SLC9A6 基因突变引起的，其特征为全面发育迟缓、癫痫、多动、共济失调、小头畸形和行为障碍。然而，这些 SLC9A6 突变导致人类 CS 的分子机制尚不完全清楚，也没有确定 SLC9A6 单一变异致病性的客观方法。
对两名疑似 CS 的个体进行基于家系的全外显子组测序（WES）。使用源自这两名患者的 EBV-LCLs 进行 qRT-PCR、western blot 分析、filipin 染色、溶酶体酶测定和电子显微镜检查。
基于家系的 WES 鉴定出先证者 1 存在 SLC9A6 c.1560dupT，p.T521Yfs23 半合子变异，先证者 2 存在 SLC9A6 c.608delA，p.H203Lfs10 半合子变异。这两名患儿均表现出与 CS 相关的典型表型。对源自这两名患者的 EBV-LCLs 的表达分析显示，mRNA 水平显著降低，且无法检测到正常的 NHE6 蛋白。患者 1 的 EBV-LCLs 在用 filipin 染色时显示胆固醇酯显著增加，但患者 2 仅显示非显著增加。患者 2 的 EBV-LCLs 中的溶酶体酶（β-己糖胺酶 A、β-己糖胺酶 A+B、β-半乳糖苷酶、半乳糖脑苷脂酶、芳基硫酸酯酶 A）活性与两名患者和六名对照者之间无显著差异。重要的是，通过电子显微镜我们在患者的 EBV-LCLs 中检测到板层膜结构的积累、变形的线粒体和脂滴。
我们患者中的 SLC9A6 p.T521Yfs23 和 p.H203Lfs10 变异导致 NHE6 缺失。线粒体和脂质代谢的改变可能在 CS 的发病机制中起作用。此外，用 filipin 染色结合患者淋巴母细胞系的电子显微镜检查可作为 CS 的一种有用的补充诊断方法。
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