Dofash Lein N H, Miles Lee B, Saito Yoshihiko, Rivas Eloy, Calcinotto Vanessa, Oveissi Sara, Serrano Rita J, Templin Rachel, Ramm Georg, Rodger Alison, Haywood Joel, Ingley Evan, Clayton Joshua S, Taylor Rhonda L, Folland Chiara L, Groth David, Hock Daniella H, Stroud David A, Gorokhova Svetlana, Donkervoort Sandra, Bönnemann Carsten G, Sud Malika, VanNoy Grace E, Mangilog Brian E, Pais Lynn, O'Donnell-Luria Anne, Madruga-Garrido Marcos, Scala Marcello, Fiorillo Chiara, Baratto Serena, Traverso Monica, Malfatti Edoardo, Bruno Claudio, Zara Federico, Paradas Carmen, Ogata Katsuhisa, Nishino Ichizo, Laing Nigel G, Bryson-Richardson Robert J, Cabrera-Serrano Macarena, Ravenscroft Gianina
Harry Perkins Institute of Medical Research, Centre for Medical Research, University of Western Australia, Perth, WA 6009, Australia.
School of Biological Sciences, Monash University, Melbourne, VIC 3800, Australia.
Brain. 2025 May 13;148(5):1707-1722. doi: 10.1093/brain/awae371.
Rigid spine syndrome is a rare childhood-onset myopathy characterized by slowly progressive or non-progressive scoliosis, neck and spine contractures, hypotonia and respiratory insufficiency. Biallelic variants in SELENON account for most cases of rigid spine syndrome, however, the underlying genetic cause in some patients remains unexplained. We used exome and genome sequencing to investigate the genetic basis of rigid spine syndrome in patients without a genetic diagnosis. In five patients from four unrelated families, we identified biallelic variants in HMGCS1 (3-hydroxy-3-methylglutaryl-coenzyme A synthase). These included six missense variants and one frameshift variant distributed throughout HMGCS1. All patients presented with spinal rigidity primarily affecting the cervical and dorso-lumbar regions, scoliosis and respiratory insufficiency. Creatine kinase levels were variably elevated. The clinical course worsened with intercurrent disease or certain drugs in some patients; one patient died from respiratory failure following infection. Muscle biopsies revealed irregularities in oxidative enzyme staining with occasional internal nuclei and rimmed vacuoles. HMGCS1 encodes a critical enzyme of the mevalonate pathway and has not yet been associated with disease. Notably, biallelic hypomorphic variants in downstream enzymes including HMGCR and GGPS1 are associated with muscular dystrophy resembling our cohort's presentation. Analyses of recombinant human HMGCS1 protein and four variants (p.S447P, p.Q29L, p.M70T, p.C268S) showed that all mutants maintained their dimerization state. Three of the four mutants exhibited reduced thermal stability, and two mutants showed subtle changes in enzymatic activity compared to the wildtype. Hmgcs1 mutant zebrafish displayed severe early defects, including immobility at 2 days and death by Day 3 post-fertilisation and were rescued by HMGCS1 mRNA. We demonstrate that the four variants tested (S447P, Q29L, M70T and C268S) have reduced function compared to wild-type HMGCS1 in zebrafish rescue assays. Additionally, we demonstrate the potential for mevalonic acid supplementation to reduce phenotypic severity in mutant zebrafish. Overall, our analyses suggest that these missense variants in HMGCS1 act through a hypomorphic mechanism. Here, we report an additional component of the mevalonate pathway associated with disease and suggest biallelic variants in HMGCS1 should be considered in patients presenting with an unresolved rigid spine myopathy phenotype. Additionally, we highlight mevalonoic acid supplementation as a potential treatment for patients with HMGCS1-related disease.
僵硬脊柱综合征是一种罕见的儿童期起病的肌病，其特征为缓慢进展或非进展性脊柱侧弯、颈部和脊柱挛缩、肌张力减退和呼吸功能不全。大多数僵硬脊柱综合征病例由SELENON基因的双等位基因变异引起，然而，部分患者潜在的遗传病因仍未明确。我们采用外显子组和基因组测序来研究未明确遗传诊断的患者中僵硬脊柱综合征的遗传基础。在来自四个无关家庭的五名患者中，我们在HMGCS1（3-羟基-3-甲基戊二酰辅酶A合酶）基因中鉴定出双等位基因变异。这些变异包括六个错义变异和一个移码变异，分布于整个HMGCS1基因。所有患者均表现出主要影响颈段和胸腰段的脊柱僵硬、脊柱侧弯和呼吸功能不全。肌酸激酶水平有不同程度升高。部分患者在并发疾病或使用某些药物后临床病程恶化；一名患者在感染后死于呼吸衰竭。肌肉活检显示氧化酶染色异常，偶见肌纤维内细胞核和镶边空泡。HMGCS1编码甲羟戊酸途径中的一种关键酶，此前尚未发现其与疾病相关。值得注意的是，包括HMGCR和GGPS1在内的下游酶的双等位基因低表达变异与类似于我们队列表现的肌营养不良有关。对重组人HMGCS1蛋白和四个变异体（p.S447P、p.Q29L、p.M70T、p.C268S）的分析表明，所有突变体均保持其二聚化状态。四个突变体中的三个表现出热稳定性降低，与野生型相比，两个突变体的酶活性有细微变化。Hmgcs1突变的斑马鱼表现出严重的早期缺陷，包括受精后2天不动，3天内死亡，而HMGCS1 mRNA可挽救这种情况。我们证明，在斑马鱼挽救试验中，所测试的四个变异体（S447P、Q29L、M70T和C268S）与野生型HMGCS1相比功能降低。此外，我们证明补充甲羟戊酸有可能降低突变斑马鱼的表型严重程度。总体而言，我们的分析表明，HMGCS1中的这些错义变异通过低表达机制起作用。在此，我们报告了甲羟戊酸途径中与疾病相关的另一个组成部分，并建议对于表现出未明确的僵硬脊柱肌病表型的患者应考虑HMGCS1基因的双等位基因变异。此外，我们强调补充甲羟戊酸是治疗HMGCS1相关疾病患者的一种潜在方法。
