1. Introduction
Nicotinamide adenine dinucleotide (NAD) has been unveiled to be essential for embryonic development. Patients with genetic variants in the NAD+ de novo synthesis pathway often have congenital NAD deficiency disorder (CNDD), a multisystem condition inherited in an autosomal recessive manner. In the context of NAD+ deficiency, all organs and systems, not just vertebrae, heart, kidneys, and limbs, may be affected.
2. The association between NAD synthetase 1 (NADSYN1) and CNDD
Individuals delivering biallelic NADSYN1 variants share similar clinical features to those with CNDD. Up till now, almost all of the identified CNDD cases can be attributed to biallelic loss-of-function variants in any of 3 nonredundant genes of the NAD de novo synthesis pathway, including kynureninase (KYNU), 3-hydroxyanthranilate 3,4-dioxygenase (HAAO), or NADSYN1. Among individuals with CNDD identified to date, those with biallelic pathogenic NADSYN1 variants are the most diverse in phenotype.
3. The impact of NADSYN1 variants upon enzymatic activity and phenotype
Specifically, NADSYN1 can catalyse the amidation of nicotinic acid adenine dinucleotide (NaAD) to NAD. Biallelic pathogenic variants in NADSYN1 cause a metabolic block in both the de novo pathway and the Preiss-Handler pathway, leading to NAD deficiency. Biallelic NADSYN1 loss-of-function variants impact the NAD metabolome of humans. Post-birth phenotypes involve feeding difficulties, developmental delay, short stature, etc.
4. Mouse embryogenesis disrupted by the loss of NADSYN1
In NADSYN1-/- mouse embryos, NAD-dependent malformations occur when maternal dietary NAD precursors are limited during gestation. The affected Nadsyn1-/- embryos most frequently present malformations of the kidneys, eyes, and lungs.
5. The preventative effect of amidated NAD precursor supplementation against CNDD
NADSYN1-dependent embryo loss and malformation in mice are preventable by dietary supplementation of amidated NAD precursors (NMN and NAM) during pregnancy. Maternal diet–derived NAD precursors primarily determine the development of healthy embryos.
6. Conclusion
NAD-boosting supplements are essential for individuals with biallelic loss-of-function variants in NADSYN1. Maternal NAD precursor supplementation, to some extent, can reduce the risk of developing CNDD.
Reference
Szot JO, Cuny H, Martin EM, et al. A metabolic signature for NADSYN1-dependent congenital NAD deficiency disorder. J Clin Invest. 2024;134(4):e174824. Published 2024 Feb 15. doi:10.1172/JCI174824
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