Expanding the clinical and genetic spectrum of CAD deficiency: an epileptic encephalopathy treatable with uridine supplementation

Abstract

Purpose

Biallelic CAD variants underlie CAD deficiency (or early infantile epileptic encephalopathy-50, [EIEE-50]), an error of pyrimidine de novo biosynthesis amenable to treatment via the uridine salvage pathway. We further define the genotype and phenotype with a focus on treatment.

Methods

Retrospective case series of 20 patients.

Results

Our study confirms CAD deficiency as a progressive EIEE with recurrent status epilepticus, loss of skills, and dyserythropoietic anemia. We further refine the phenotype by reporting a movement disorder as a frequent feature, and add that milder courses with isolated developmental delay/intellectual disability can occur as well as onset with neonatal seizures. With no biomarker available, the diagnosis relies on genetic testing and functional validation in patient-derived fibroblasts. Underlying pathogenic variants are often rated as variants of unknown significance, which could lead to underrecognition of this treatable disorder. Supplementation with uridine, uridine monophosphate, or uridine triacetate in ten patients was safe and led to significant clinical improvement in most patients.

Conclusion

We advise a trial with uridine (monophosphate) in all patients with developmental delay/intellectual disability, epilepsy, and anemia; all patients with status epilepticus; and all patients with neonatal seizures until (genetically) proven otherwise or proven unsuccessful after 6 months. CAD deficiency might represent a condition for genetic newborn screening.

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Fig. 1: Pyrimidine synthesis: de novo versus salvage pathway and Neuroimaging in CAD-deficiency.
Fig. 2: Distribution of novel and known variants in the CAD gene and The effect of supplementing the growth medium with uridine.

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Acknowledgements

We thank Ms. Schittek (Sana Pharmacy, Düsseldorf, Germany) for ongoing efforts to provide UMP to the patients in Germany and Austria. This work was funded by the Jubiläumsfonds of the OeNB (number 18023) and a research grant restricted to CAD deficiency provided by Milupa metabolics to S.B.W.

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DR, JAM, JB and SBW are responsible for study design, evaluation of data, and writing of the manuscript. All authors read the manuscript and contributed intellectual content.

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Correspondence to Saskia B. Wortmann MD, PhD.

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Rymen, D., Lindhout, M., Spanou, M. et al. Expanding the clinical and genetic spectrum of CAD deficiency: an epileptic encephalopathy treatable with uridine supplementation. Genet Med 22, 1589–1597 (2020). https://doi.org/10.1038/s41436-020-0933-z

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Keywords

  • anemia
  • epilepsy
  • developmental delay
  • early infantile epileptic encephalopathy-50
  • EIEE

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