Friday, May 1, 2020

CAD deficiency: a neurometabolic disorder treatable with uridine

Zhou L, Xu H, Wang T, Wu Y. A Patient With CAD Deficiency Responsive to Uridine and Literature Review. Front Neurol. 2020 Feb 5;11:64. doi:10.3389/fneur.2020.00064.

CAD encodes a multifunctional enzyme involved in de novo pyrimidine biosynthesis, and pyrimidine can be alternatively recycled from uridine. Trio whole-exome sequencing identified CAD compound heterozygous mutations in a new male patient with global developmental delay (DD), refractory epilepsy, and anemia with anisopoikilocytosis. We further reviewed all published cases with CAD deficiency. Five patients were collected from two publications, including three males and two females, and all presented with DD, drug-resistant epilepsy, and anemia with anisopoikilocytosis. Four out of six patients (including the present case) were supplemented with uridine, which led to immediate cessation of seizures, resolved anemia with anisopoikilocytosis, and progress in global development. The other two patients, who were not treated with uridine, died at the ages of 4 and 5 years. In summary, CAD deficiency is probably a treatable neurometabolic disorder.

Koch J, Mayr JA, Alhaddad B, Rauscher C, Bierau J, Kovacs-Nagy R, Coene KL, Bader I, Holzhacker M, Prokisch H, Venselaar H, Wevers RA, Distelmaier F, Polster T, Leiz S, Betzler C, Strom TM, Sperl W, Meitinger T, Wortmann SB, Haack TB. CAD mutations and uridine-responsive epileptic encephalopathy. Brain. 2017 Feb;140(2):279-286.

Unexplained global developmental delay and epilepsy in childhood pose a major socioeconomic burden. Progress in defining the molecular bases does not often translate into effective treatment. Notable exceptions include certain inborn errors of metabolism amenable to dietary intervention. CAD encodes a multifunctional enzyme involved in de novo pyrimidine biosynthesis. Alternatively, pyrimidines can be recycled from uridine. Exome sequencing in three families identified biallelic CAD mutations in four children with global developmental delay, epileptic encephalopathy, and anaemia with anisopoikilocytosis. Two died aged 4 and 5 years after a neurodegenerative disease course. Supplementation of the two surviving children with oral uridine led to immediate cessation of seizures in both. A 4-year-old female, previously in a minimally conscious state, began to communicate and walk with assistance after 9 weeks of treatment. A 3-year-old female likewise showed developmental progress. Blood smears normalized and anaemia resolved. We establish CAD as a gene confidently implicated in this neurometabolic disorder, characterized by co-occurrence of global developmental delay, dyserythropoietic anaemia and seizures. While the natural disease course can be lethal in early childhood, our findings support the efficacy of uridine supplementation, rendering CAD deficiency a treatable neurometabolic disorder and therefore a potential condition for future (genetic) newborn screening.

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