Gupta Swati, Fahiminiya Somayyeh, Wang Tracy, Dempsey Nunez Laura, Rosenblatt David S, Gibson William T, Gilfix Brian, Bergeron John J M, Jerome-Majewska Loydie A
Department of Human Genetics, McGill University, Montreal, Quebec H3A 1B1, Canada;
Department of Human Genetics, McGill University, Montreal, Quebec H3A 1B1, Canada;; Department of Pediatrics, McGill University, Montreal, Quebec H4A 3J1, Canada;
Cold Spring Harb Mol Case Stud. 2016 May;2(3):a000737. doi: 10.1101/mcs.a000737.
Using whole-exome sequencing, we identified homozygous mutations in two unlinked genes, SEC23A c.1200G>C (p.M400I) and MAN1B1 c.1000C>T (p.R334C), associated with congenital birth defects in two patients from a consanguineous family. Patients presented with carbohydrate-deficient transferrin, tall stature, obesity, macrocephaly, and maloccluded teeth. The parents were healthy heterozygous carriers for both mutations and an unaffected sibling with tall stature carried the heterozygous mutation in SEC23A only. Mutations in SEC23A are responsible for craniolenticosultura dysplasia (CLSD). CLSD patients are short, have late-closing fontanels, and have reduced procollagen (pro-COL1A1) secretion because of abnormal pro-COL1A1 retention in the endoplasmic reticulum (ER). The mutation we identified in MAN1B1 was previously associated with reduced MAN1B1 protein and congenital disorders of glycosylation (CDG). CDG patients are also short, are obese, and have abnormal glycan remodeling. Molecular analysis of fibroblasts from the family revealed normal levels of SEC23A in all cells and reduced levels of MAN1B1 in cells with heterozygous or homozygous mutations in SEC23A and MAN1B1. Secretion of pro-COL1A1 was increased in fibroblasts from the siblings and patients, and pro-COL1A1 was retained in Golgi of heterozygous and homozygous mutant cells, although intracellular pro-COL1A1 was increased in patient fibroblasts only. We postulate that increased pro-COL1A1 secretion is responsible for tall stature in these patients and an unaffected sibling, and not previously discovered in patients with mutations in either SEC23A or MAN1B1. The patients in this study share biochemical and cellular characteristics consistent with mutations in MAN1B1 and SEC23A, indicating a digenic disease.
通过全外显子组测序，我们在一个近亲家庭的两名患者中发现了两个不连锁基因中的纯合突变，即SEC23A基因的c.1200G>C（p.M400I）和MAN1B1基因的c.1000C>T（p.R334C），这些突变与先天性出生缺陷相关。患者表现出转铁蛋白缺乏、身材高大、肥胖、巨头畸形和牙齿咬合不正。父母是这两种突变的健康杂合携带者，一名身材高大的未受影响的同胞仅携带SEC23A基因的杂合突变。SEC23A基因突变导致颅骨缝早闭发育不良（CLSD）。CLSD患者身材矮小，囟门闭合延迟，由于前胶原（pro-COL1A1）在内质网（ER）中异常滞留，前胶原（pro-COL1A1）分泌减少。我们在MAN1B1基因中鉴定出的突变先前与MAN1B1蛋白减少和糖基化先天性疾病（CDG）有关。CDG患者也身材矮小、肥胖，并且有异常的聚糖重塑。对该家族成纤维细胞的分子分析显示，所有细胞中SEC23A水平正常，而在SEC23A和MAN1B1基因有杂合或纯合突变的细胞中，MAN1B1水平降低。同胞和患者的成纤维细胞中前胶原（pro-COL1A1）的分泌增加，前胶原（pro-COL1A1）保留在杂合和纯合突变细胞的高尔基体中，尽管仅在患者成纤维细胞中细胞内前胶原（pro-COL1A1）增加。我们推测，前胶原（pro-COL1A1）分泌增加是这些患者和一名未受影响的同胞身材高大的原因，而在SEC23A或MAN1B1基因突变的患者中尚未发现这一现象。本研究中的患者具有与MAN1B1和SEC23A基因突变一致的生化和细胞特征，表明这是一种双基因疾病。
