Cottrell Emily, Maharaj Avinaash, Williams Jack, Chatterjee Sumana, Cirillo Grazia, Miraglia Del Giudice Emanuele, Festa Adalgisa, Palumbo Stefania, Capalbo Donatella, Salerno Mariacarolina, Pignata Claudio, Savage Martin O, Schilbach Katharina, Bidlingmaier Martin, Hwa Vivian, Metherell Louise A, Grandone Anna, Storr Helen L
Centre for Endocrinology, William Harvey Research Institute: Barts and The London School of Medicine and Dentistry William Harvey Research Institute, London EC1M 6BQ, UK.
Studies of Campania Luigi Vanvitelli, Department of Woman, Child, General and Specialized Surgery, Naples 80138, Italy.
J Clin Endocrinol Metab. 2021 Jul 28. doi: 10.1210/clinem/dgab550.
Severe forms of growth hormone insensitivity (GHI) are characterized by extreme short stature, dysmorphism, and metabolic anomalies.
This work aims to identify the genetic cause of growth failure in 3 "classical" GHI individuals.
A novel intronic growth hormone receptor gene (GHR) variant was identified, and in vitro splicing assays confirmed aberrant splicing. A 6Ω pseudoexon GHR vector and patient fibroblast analysis assessed the consequences of the novel pseudoexon inclusion and the impact on GHR function.
We identified a novel homozygous intronic GHR variant (g.5:42700940T > G, c.618+836T > G), 44 bp downstream of the previously recognized intronic 6Ψ GHR pseudoexon mutation in the index patient. Two siblings also harbored the novel intronic 6Ω pseudoexon GHR variant in compound heterozygosity with the known GHR c.181C > T (R43X) mutation. In vitro splicing analysis confirmed inclusion of a 151-bp mutant 6Ω pseudoexon not identified in wild-type constructs. Inclusion of the 6Ω pseudoexon causes a frameshift resulting in a nonfunctional truncated GHR lacking the transmembrane and intracellular domains. The truncated 6Ω pseudoexon protein demonstrated extracellular accumulation and diminished activation of STAT5B signaling following GH stimulation.
Novel GHR 6Ω pseudoexon inclusion results in loss of GHR function consistent with a severe GHI phenotype. This represents a novel mechanism of Laron syndrome and is the first deep intronic variant identified causing severe postnatal growth failure. The 2 kindreds originate from the same town in Campania, Southern Italy, implying common ancestry. Our findings highlight the importance of studying variation in deep intronic regions as a cause of monogenic disorders.
严重形式的生长激素不敏感（GHI）的特征是身材极度矮小、畸形和代谢异常。
本研究旨在确定3例“典型”GHI患者生长发育迟缓的遗传原因。
鉴定出一种新的内含子生长激素受体基因（GHR）变异体，体外剪接试验证实剪接异常。构建一个含6Ω假外显子的GHR载体并对患者成纤维细胞进行分析，以评估新的假外显子插入的后果及其对GHR功能的影响。
我们在索引患者中发现了一种新的纯合内含子GHR变异体（g.5:42700940T>G，c.618+836T>G），位于先前识别的内含子6Ψ GHR假外显子突变下游44bp处。两名同胞也携带这种新的内含子6Ω假外显子GHR变异体，与已知的GHR c.181C>T（R43X）突变呈复合杂合状态。体外剪接分析证实野生型构建体中未发现的一个151bp突变型6Ω假外显子被包含在内。6Ω假外显子的插入导致移码突变，产生一个缺乏跨膜和细胞内结构域的无功能截短GHR。截短的6Ω假外显子蛋白在生长激素刺激后表现出细胞外积聚和STAT5B信号激活减弱。
新的GHR 6Ω假外显子插入导致GHR功能丧失，与严重的GHI表型一致。这代表了拉伦综合征的一种新机制，是首次鉴定出的导致严重出生后生长发育迟缓的深度内含子变异体。这两个家族来自意大利南部坎帕尼亚的同一个城镇，暗示有共同的祖先。我们的研究结果强调了研究深度内含子区域变异作为单基因疾病病因的重要性。
