National Institutes of Health Clinical Center, Bethesda, MD, USA.
The Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
Mol Genet Genomic Med. 2021 Feb;9(2):e1556. doi: 10.1002/mgg3.1556. Epub 2020 Dec 17.
Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is an autosomal recessive disease of steroidogenesis that affects 1 in 15,000. Approximately, 10% of the CAH population also suffer from CAH-X, a connective tissue dysplasia consistent with hypermobility type Ehlers-Danlos syndrome (EDS). Most patients with CAH-X carry a contiguous gene deletion involving CYP21A2 encoding 21-hydroxylase and TNXB encoding tenascin-X (TNX), but some are of unknown etiology.
We conducted clinical evaluation and medical history review of EDS-related manifestations in subjects from two unrelated CAH families who carry a heterozygous TNXB c.12463+2T>C variant that alters the splice donor site of intron 42. A next generation sequencing (NGS) based EDS panel composed of 45 genes was performed for index patients from each family. TNX expression in patient skin biopsy tissues and dermal fibroblasts was assessed by qRT-PCR and Sanger sequencing.
All three evaluated CAH patients carrying the TNXB splice site variant had moderate EDS manifestations. An NGS panel excluded involvement of other known EDS-related variants. RNA assay on skin biopsies and dermal fibroblasts did not detect splicing errors in TNX mRNA; however, the removal of intron 42 was less efficient in the allele harboring the splice site variant as evidenced by the existence of a premature TNX RNA form, leading to an allele specific decrease in TNX mRNA.
Carrying a TNXB c.12463+2T>C variant at the intron 42 splice donor site causes an allele specific decrease in TNX expression, which can be associated with moderate EDS in CAH patients.
由于 21-羟化酶缺乏导致的先天性肾上腺增生（CAH）是一种影响 1/15000 的类固醇生成的常染色体隐性遗传病。大约 10%的 CAH 人群还患有 CAH-X，这是一种与 Ehlers-Danlos 综合征（EDS）高迁移率型一致的结缔组织发育不良。大多数 CAH-X 患者携带涉及 CYP21A2 编码 21-羟化酶和 TNXB 编码 tenascin-X（TNX）的连续基因缺失，但有些病因不明。
我们对两个无关的 CAH 家族中携带异质 TNXB c.12463+2T>C 变体的 EDS 相关表现进行了临床评估和病史回顾，该变体改变了内含子 42 的剪接受体位点。对每个家族的索引患者进行了基于下一代测序（NGS）的 EDS 面板检测，该面板由 45 个基因组成。通过 qRT-PCR 和 Sanger 测序评估患者皮肤活检组织和真皮成纤维细胞中的 TNX 表达。
所有 3 名携带 TNXB 剪接位点变体的评估 CAH 患者均有中度 EDS 表现。NGS 面板排除了其他已知 EDS 相关变体的参与。对皮肤活检和真皮成纤维细胞的 RNA 检测未检测到 TNX mRNA 的剪接错误；然而，在携带剪接位点变体的等位基因中，内含子 42 的去除效率较低，这表现为存在一种过早的 TNX RNA 形式，导致 TNX mRNA 呈等位基因特异性减少。
携带内含子 42 剪接供体位点的 TNXB c.12463+2T>C 变体导致 TNX 表达呈等位基因特异性减少，这可能与 CAH 患者的中度 EDS 相关。
