Protein O-fucosyltransferase-1 (POFUT1) adds O-fucose monosaccharides to epidermal growth factor-like (EGF) repeats found on approximately 100 mammalian proteins, including Notch receptors. Haploinsufficiency of POFUT1 has been linked to adult-onset Dowling Degos Disease (DDD) with hyperpigmentation defects. Homozygous deletion of mouse Pofut1 results in embryonic lethality with severe Notch-like phenotypes including defects in somitogenesis, cardiogenesis, vasculogenesis and neurogenesis, but the extent to which POFUT1 is required for normal human development is not yet understood. Here we report a patient with a congenital syndrome consisting of severe global developmental delay, microcephaly, heart defects, failure to thrive and liver disease with a previously unreported homozygous NM_015352.1: c.485C>T variant (p.Ser162Leu) in POFUT1 detected by exome sequencing. Both parents are heterozygotes and neither manifests any signs of DDD. No other detected variant explained the phenotype. This variant eliminated a conserved N-glycosylation sequon at Asn160 in POFUT1 and profoundly decreased POFUT1 activity in patient fibroblasts compared to control fibroblasts. Purified p.Ser162Leu mutant protein also showed much lower POFUT1 activity with a lower affinity for EGF acceptor substrate than wild type POFUT1. Eliminating the N-glycan sequon by replacing Asn160 with Gln had little effect on POFUT1 activity, suggesting that loss of the glycan is not responsible for the defect. Furthermore, the p.Ser162Leu mutant showed weaker ability to rescue Notch activity in cell-based assays. These results suggest that this N-glycan of POFUT1 is not required for its proper enzymatic function, and that the p.Ser162Leu mutation of POFUT1 likely causes global developmental delay, microcephaly with vascular and cardiac defects.

中文翻译：

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人POFUT1的变异会降低酶的活性，并可能导致隐性小头畸形，整体发育延迟，并伴有心脏和血管特征

O-岩藻糖基转移酶-1（POFUT1）蛋白将O-岩藻糖单糖添加到在包括Notch受体在内的大约100种哺乳动物蛋白质中发现的表皮生长因子样（EGF）重复序列中。POFUT1的单倍剂量不足与成人色素沉着缺陷的Dowling Degos病（DDD）有关。小鼠Pofut1的纯合缺失导致严重Notch的胚胎致死率类表型，包括体发生，心脏发生，血管发生和神经发生中的缺陷，但POFUT1正常人类发育所需的程度尚不清楚。在这里，我们报道了一位先天性综合征患者，包括严重的全球发育迟缓，小头畸形，心脏缺陷，failure壮衰竭和肝病，此前未报道纯合子NM_015352.1：在POFUT1中检测到c.485C> T变体（p.Ser162Leu）通过外显子组测序。父母双方都是杂合子，都没有表现出DDD的迹象。没有其他检测到的变体解释该表型。此变体消除了保守的N与对照成纤维细胞相比，POFUT1中Asn160的糖基化序列会显着降低患者成纤维细胞中POFUT1的活性。纯化的p.Ser162Leu突变蛋白也显示出比野生型POFUT1低得多的POFUT1活性，对EGF受体底物的亲和力也低。通过用Gln替代Asn160来消除N-聚糖序列对POFUT1活性的影响很小，这表明聚糖的丢失与缺陷无关。此外，在基于细胞的测定中，p.Ser162Leu突变体显示出较弱的抢救Notch活性的能力。这些结果表明，POFUT1的这种N-聚糖不是其适当的酶功能所必需的，并且POFUT1的p.Ser162Leu突变可能导致整体发育延迟，具有血管和心脏缺陷的小头畸形。