Nucleotide metabolism is a complex pathway regulating crucial cellular processes such as nucleic acid synthesis, DNA repair and proliferation. This study shows that impairment of the biosynthesis of one of the building blocks of DNA, dTTP, causes a severe, early-onset neurodegenerative disease. Here, we describe two unrelated children with bi-allelic variants in DTYMK, encoding dTMPK, which catalyzes the penultimate step in dTTP biosynthesis. The affected children show severe microcephaly and growth retardation with minimal neurodevelopment. Brain imaging revealed severe cerebral atrophy and disappearance of the basal ganglia. In cells of affected individuals, dTMPK enzyme activity was minimal, along with impaired DNA replication. In addition, we generated dtymk mutant zebrafish that replicate this phenotype of microcephaly, neuronal cell death and early lethality. An increase of ribonucleotide incorporation in the genome as well as impaired responses to DNA damage were observed in dtymk mutant zebrafish, providing novel pathophysiological insights. It is highly remarkable that this deficiency is viable as an essential component for DNA cannot be generated, since the metabolic pathway for dTTP synthesis is completely blocked. In summary, by combining genetic and biochemical approaches in multiple models we identified loss-of-function of DTYMK as the cause of a severe postnatal neurodegenerative disease and highlight the essential nature of dTTP synthesis in the maintenance of genome stability and neuronal survival.

核苷酸代谢是一个复杂的途径，调节关键的细胞过程，如核酸合成、DNA 修复和增殖。这项研究表明，DNA 的组成部分之一 dTTP 的生物合成受损会导致严重的早发性神经退行性疾病。在这里，我们描述了两个在DTYMK中具有双等位基因变异的不相关儿童，编码 dTMPK，它催化 dTTP 生物合成的倒数第二步。受影响的儿童表现出严重的小头畸形和生长迟缓，神经发育极少。脑成像显示严重的脑萎缩和基底节消失。在受影响个体的细胞中，dTMPK 酶活性最小，同时 DNA 复制受损。另外，我们生成了 dtymk突变斑马鱼复制了小头畸形、神经元细胞死亡和早期致死的这种表型。在dtymk突变斑马鱼中观察到基因组中核糖核苷酸掺入的增加以及对 DNA 损伤的反应受损，提供了新的病理生理学见解。非常值得注意的是，这种缺陷是可行的，因为不能产生 DNA 的必需成分，因为 dTTP 合成的代谢途径被完全阻断。总之，通过在多个模型中结合遗传和生化方法，我们确定DTYMK的功能丧失是严重的产后神经退行性疾病的原因，并强调了 dTTP 合成在维持基因组稳定性和神经元存活中的本质。