The vital cofactors NADH and NADPH are prone to hydration, forming hydroxylated redox-inactive derivatives (NADHX and NADPHX) in cells. These damaged metabolites are repaired by two highly conserved enzymes, an NAD(P)HX dehydratase (NAXD) and an NAD(P)HX epimerase (NAXE). Mutations in NAXE or NAXD cause early onset progressive encephalopathy (PEBEL1 or PEBEL2), typically induced by fever or other triggers, and leading to premature death. To advance our comprehension of the disease mechanism and investigate potential therapeutic strategies, we generated zebrafish lines deficient in naxe or naxd using CRISPR/Cas9 technology. While both models accumulated NADHX, only naxd-/- larvae developed a severe phenotype, showing reduced locomotion and early death, which was partially rescued by nicotinic acid supplementation. Both mutant lines displayed signs of dysregulated immune function based on gene expression analyses and increased neutral red staining in the head region, indicating an increased number or activation of microglial cells. Our findings suggest that immune system perturbations play a role in PEBEL disease development, aligning with its inflammatory trigger-induced nature in humans. The naxd-/- model's responsiveness to nicotinic acid underscores its utility for preclinical drug screening. Overall, these models will be instrumental in furthering our understanding of PEBEL disease mechanisms and enhancing translational research efforts.

This study aims to explore the clinical characteristics of patients with NAD(P)HX metabolic deficiency and their prognosis after nicotinamide treatment. This study retrospectively analyzed the clinical characteristics, efficacy of nicotinamide treatment, and prognosis of patients with genetically confirmed NAD(P)HX metabolic defects admitted to Beijing Children’s Hospital from January 2016 to January 2025, as well as cases previously reported in the literature. The log-rank test was used for survival analysis, and the prognosis was evaluated using the Modified Rankin Scale (mRS). Nine patients were analyzed, including eight with NAXE deficiency and one with NAXD deficiency, seven of whom received nicotinamide treatment (180–500 mg/day). With a median follow-up of 3.92 years [range: 0.50–6 years, interquartile range (IQR) = 2.42 years], the overall prognosis was favourable. All seven treated patients survived, three of whom were able to attend school normally, and no significant adverse reactions were observed during treatment. Combined with previous studies, a total of 59 patients were included for analysis (14 cases of NAXD deficiency and 45 cases of NAXE deficiency), with an overall mortality rate of 66.7%. Among the 21 patients who received niacin/nicotinamide treatment, 17 survived (80.95%), whereas only two untreated patients survived, and 85.45% of the untreated patients died within 2 years of onset. Respiratory failure was the most common cause of death. NAD(P)HX metabolic defects are rare mitochondrial diseases with high mortality and morbidity rates. Early identification and timely initiation of nicotinamide treatment are crucial for improving patient prognosis and quality of life. The online version contains supplementary material available at 10.1186/s13023-026-04218-4.

ATP-dependent (S)-NAD(P)H-hydrate dehydratase (NAXD) is a crucial enzyme in the nicotinamide adenine dinucleotide repair system that regenerates NAD(P)H, an essential electron donor in metabolic redox reactions. NAD+-related metabolic pathways connect cellular metabolism and the expression of genes responsible for adipogenesis; however, the biological significance of the NAXD-mediated repair pathway remains unclear. Herein, we showed that NAXD is essential for normal adipocyte differentiation of 3T3-L1 murine preadipocytes. Silencing of the Naxd gene attenuated differentiation-induced lipid accumulation with excessive accumulation of hydrated NADH (NADHX) without altering NAD+ levels. FK866, a specific inhibitor of NAMPT, further reduced lipid accumulation even in Naxd-silenced cells with substantial decrease in NAD+. Supplementation with nicotinamide mononucleotide, a precursor of NAD+, restored NAD+ levels comparably in Naxd- and LacZ-silenced cells treated with FK866, but failed to recover adipocyte differentiation of Naxd-silenced cells to the level of LacZ-silenced cells. In contrast, exposure of wild-type 3T3-L1 cells to NADHX recapitulated the Naxd deficiency-elicited inhibitory effects on adipocyte differentiation with reduced expression of master transcriptional regulators of adipogenesis, peroxisome proliferator-activated receptor γ and CCAAT/enhancer binding protein α. These results suggest that NAXD supports normal adipogenesis, in part, by inhibiting excessive accumulation of NADHX.

NAD(P)HX dehydratase (NAXD) gene is one of the key enzymes encoding the nicotinamide nucleotide repair system, reportedly associated with Encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy, 2 (PEBEL2). Here, we generated an induced pluripotent stem cell (iPSC) line from the dermal fibroblasts (HDFs) of a PEBEL2 patient who carried biallelic mutations, c.101_102delTA(p.Thr35Phefs*63) and c.318C > G (p.Ile160Met) in NAXD. These iPSCs showed stable amplification in vitro, expressed pluripotent markers, and differentiated spontaneously into three germ layers, as well as NAXD mutations with normal karyotype.

Metabolic pathways are known to generate byproducts-some of which have no clear metabolic function and some of which are toxic. Nicotinamide adenine dinucleotide phosphate hydrate (NAD(P)HX) is a toxic metabolite that is produced by stressors such as a fever, infection, or physical stress. Nicotinamide adenine dinucleotide phosphate hydrate dehydratase (NAXD) and nicotinamide adenine dinucleotide phosphate hydrate epimerase (NAXE) are part of the nicotinamide repair system that function to break down this toxic metabolite. Deficiency of NAXD and NAXE interrupts the critical intracellular repair of NAD(P)HX and allows for its accumulation. Clinically, deficiency of NAXE manifests as progressive, early onset encephalopathy with brain edema and/or leukoencephalopathy (PEBEL) 1, while deficiency of NAXD manifests as PEBEL2. In this report, we describe a case of probable PEBEL2 in a patient with a variant of unknown significance (c.362C>T, p.121L) in the NAXD gene who presented after routine immunizations with significant skin findings and in the absence of fevers.