He H, Zhang H, Chen H, He F, Yin F, Stauber T, Zou X, Peng J. Functional analysis of two
SLC9A6 frameshift variants in lymphoblastoid cells from patients with Christianson syndrome.
CNS Neurosci Ther 2023;
29:4059-4069. [PMID:
37381736 PMCID:
PMC10651982 DOI:
10.1111/cns.14329]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Revised: 05/30/2023] [Accepted: 06/17/2023] [Indexed: 06/30/2023] Open
Abstract
BACKGROUND
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.
METHODS
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.
RESULTS
Trio-based WES identified a hemizygous SLC9A6 c.1560dupT, p.T521Yfs*23 variant in proband 1 and a hemizygous SLC9A6 c.608delA, p.H203Lfs*10 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.
CONCLUSIONS
The SLC9A6 p.T521Yfs*23 and p.H203Lfs*10 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.
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