Hereditary orotic aciduria (HOA) is a very rare inborn error of pyrimidine metabolism. It results from a defect of the uridine-5-monophosphate synthase (UMPS) gene. To date, only about twenty patients have been described. We report a case of HOA with a novel variant in the UMPS gene. A 17-year-old Emirati girl was born to first-cousin parents. During the first year, she had recurrent, severe infections including disseminated varicella. After evaluation for immunodeficiency, an impression of immunodeficiency of unknown etiology was presumed. Frequent episodes of pancytopenia were also noted. Bone marrow biopsy showed trilineage megaloblastoid maturation with dysplastic changes that were refractory to hematinic therapy. Also, she was noted to have failure to thrive, developmental delay and epilepsy. She was referred to the Genetics clinic where whole-exome sequencing (WES) was done and showed a novel homozygous variant in the UMPS gene confirming a diagnosis of HOA. She was started on uridine triacetate after which she showed clinical, hematologic and biochemical improvement. Although extremely rare, hereditary orotic aciduria should be suspected in any child with megaloblastic bone marrow, immunodeficiency or when developmental delay and anemia coexist.

遗传性性尿酸尿症（HOA）是嘧啶代谢的一种非常罕见的先天性错误。它是由尿苷5一磷酸合酶（UMPS）基因的缺陷引起的。迄今为止，仅描述了约二十名患者。我们在UMPS中报告了一种带有新颖变体的HOA案例基因。一位17岁的阿联酋女孩出生于表兄弟姐妹的父母。在第一年中，她反复出现了严重的感染，包括弥漫性水痘。在评估免疫缺陷后，推测病因不明的免疫缺陷印象。还注意到全血细胞减少症的频繁发作。骨髓活检显示三系巨细胞样成熟，伴有增生性治疗难治的增生性改变。此外，她还被发现没有ive壮成长，发育迟缓和癫痫病。她被转介至遗传学诊所，在那里完成了全外显子组测序（WES），并在UMPS中显示出一种新的纯合变异体证实HOA诊断的基因。她开始使用三乙酸尿苷，之后显示出临床，血液学和生化方面的改善。尽管极为罕见，但对于任何患有巨幼细胞骨髓，免疫缺陷或发育迟缓和贫血并存的儿童，都应怀疑遗传性尿酸尿。