NAD+ and Rare Diseases: The Shared Biology Behind Orphan Conditions

Expert-reviewed by Dr. Vilhelm Bohr, M.D., Ph.D., D.Sc.

Key Takeaways

• Shared mechanism: Many genetically distinct rare diseases converge on the same downstream problems: mitochondrial failure, impaired DNA repair, and NAD+ disruption.
• Preclinical proof‑of‑concept: In multiple models of DNA‑repair disorders, progeroid syndromes, and mitochondrial diseases, restoring NAD+ improves mitophagy, mitochondrial function, and survival.
• Early human signals: Small trials suggest that NAD+ precursors can improve clinical markers and function in conditions like mitochondrial myopathy, Werner’s syndrome, Friedreich’s ataxia, and ataxia‑telangiectasia, though evidence is still early.
• Not a silver bullet: Mixed results in diseases like Duchenne muscular dystrophy show that NAD+ repletion alone is unlikely to be curative and will need to be combined with other targeted therapies.
• Broader implications: Because these disorders compress decades of “normal” aging biology into a short timeframe, they offer a powerful model for NAD‑targeted, mechanism‑driven interventions that could inform treatments well beyond rare disease.

For the millions of people living with a rare disease, the road to answers is rarely straightforward—most go years without a diagnosis, and often never find a treatment. They navigate a maze of misdiagnoses, dismissed symptoms, and specialists who have never encountered their condition before—sometimes remaining in that maze for years, sometimes for a lifetime. These rare conditions, often called “orphan diseases,” span every organ system and every stage of life.

On the surface, these diseases appear to be very different. However, emerging research points to the same underlying breakdown: a crisis in cellular energy production, DNA repair, and mitochondrial function—all of which are tied, at least in part, to a depletion of the vital coenzyme nicotinamide adenine dinucleotide (NAD+).¹ The implication is significant: diseases once seen as entirely unrelated may share a common vulnerability—and, therefore, a potential common therapeutic lever. In this article, we’ll explore that connection, examining what orphan diseases are, what drives them at the cellular level, and how NAD+ depletion may sit at the center of it all. We’ll take a disease-by-disease look at the published research linking declining NAD+ to specific rare conditions—and what that science might mean for the patients and researchers navigating this often-underexplored frontier.

What Is an Orphan Disease? Understanding Rare Conditions That Collectively Affect Millions

The term “orphan disease” is often used interchangeably with “rare disease,” but the word “orphan” carries a specific meaning, tracing back to the idea that these diseases—with their often very small patient populations—had been abandoned by both clinical research funding and the pharmaceutical industry. Because so few people tended to share any one rare diagnosis, there was historically little financial incentive to develop drugs or treatments for them.

However, while individually rare, orphan diseases are collectively not a small number. Across more than 7,000 known rare diseases, an estimated 300 million people worldwide are affected. Still, more than 95% of these conditions have no approved FDA treatment, and the average patient waits nearly five years for a confirmed diagnosis, often navigating a gauntlet of misdiagnoses, clinical dead ends, and limited awareness of their condition even after finally receiving one.²

Approximately 80% of orphan diseases are genetic in origin, and 70% first manifest in childhood,³ meaning families are often managing a progressive and life-limiting condition with little guidance and few options. Despite the enormous diversity among these thousands of diseases—spanning different genes, organ systems, and clinical presentations—researchers are increasingly finding that many orphan diseases share similar underlying biological mechanisms. This includes a breakdown in cellular energy production, DNA repair, and mitochondrial function—and central to these processes is a single molecule—NAD+. This is particularly relevant for the many orphan diseases that exhibit aspects of an accelerated aging process.

NAD+, DNA Repair, and Mitochondria: The Biological Breakdown Behind Rare Disease

NAD+ is a coenzyme found in every living cell. While it has many critical functions, two of its core roles are especially relevant to orphan diseases: cellular energy production and DNA repair. On the energy side, NAD+ acts as an electron carrier in the mitochondria, helping to create fuel from the food we eat.⁴ It also stimulates the process of mitophagy, which is how cells get rid of damaged mitochondria. If these damaged mitochondria remain in the cells, it is detrimental to cellular functions. On the repair side, NAD+ is used as fuel by enzymes called PARPs, which detect and initiate repairs of damaged DNA.⁵

Under normal conditions, this system works in balance. But when DNA damage accumulates, whether from aging, disease, or a genetic defect, PARP enzymes can go into overdrive, consuming NAD+ faster than cells can replenish it.⁶ The result is a damaging cascade of depleted NAD+ driving mitochondrial dysfunction, followed by impaired mitochondria generating oxidative stress, and oxidative damage causing further DNA damage.¹ Over time, this self-reinforcing cycle drives progressive cellular degeneration and sometimes cell death. 

This cycle mirrors the one that drives normal cellular aging—just on a more dramatically accelerated timeline. In many orphan diseases, a single genetic defect compresses what would typically unfold over decades into years or even months, making these patients' cells biochemically resemble those of someone far older.⁷ This accelerated “aging” is why children with certain rare conditions show signs of premature aging and why their mitochondria fail early.⁸ Because this breakdown follows a shared biochemical logic, NAD+ has emerged as a potential therapeutic target across multiple orphan diseases. 

Preclinical research and a growing number of human studies suggest that replenishing NAD+ may affect the cycle and support mitochondrial function. The science is still evolving, but the mechanistic rationale is strong—and it’s driving a new wave of investigation into what NAD+ replenishment might offer patients and families with few other options.

Orphan Diseases & Their Connection to NAD+: A Condition-by-Condition Breakdown

Although each disease covered in this section has its own distinct genetic origin, many arrive at the same biochemical destination: mitochondrial dysfunction, impaired DNA repair, and progressive degeneration in the tissues that depend most heavily on cellular energy. Conditions like Friedreich’s ataxia, Leigh syndrome, and Duchenne muscular dystrophy are among the more recognized names in the rare mitochondrial and neuromuscular disease space. But the research connecting NAD+ depletion to orphan diseases extends well beyond these, reaching into DNA repair disorders like ataxia-telangiectasia and Cockayne syndrome, progeroid conditions like Werner syndrome and Hutchinson-Guilford syndrome, and mitochondrial diseases including Alpers disease, Barth syndrome, and mitochondrial myopathy.

Across these conditions, the common thread is the same cascade described above: impaired energy metabolism, elevated oxidative stress, and the failure of cellular maintenance and repair systems that normally keep damage in check. Most of the orphan disease research with a connection to NAD+ has been done with its precursors—primarily nicotinamide riboside (NR), followed by a smaller number of studies using nicotinamide mononucleotide (NMN) and niacin. In the sections that follow, we examine each of these conditions in turn, the research connecting them to NAD+, and what that science may mean for patients and clinicians.

Alpers Disease

Alpers disease (also called Alpers syndrome or Alpers-Huttenlocher syndrome) is a rare and progressive neurodegenerative disorder affecting 1 in 40,000 individuals and caused by mutations in the POLG gene, which encodes the main and essential enzyme for replicating mitochondrial DNA. It primarily affects the brain, vision, muscles, and liver (organs with greater energy demands), leading to a progressive depletion of mitochondrial DNA that impedes the cell’s ability to produce energy. Alpers disease typically presents in early childhood—most commonly between ages 2 and 4—and causes intractable seizures, developmental regression, muscle weakness, and liver failure. It is invariably fatal, and no disease-modifying treatment currently exists. 

The NAD+ connection in Alpers disease runs through its mitochondrial pathology. Patient-derived cells show pronounced dysregulation of the NADH pathway, as well as depleted mitochondrial DNA and Complex I, the primary enzyme that regenerates NAD+ from NADH in the electron transport chain.⁹ In a 2024 preclinical study, researchers used iPSC-derived cortical organoids—lab-grown brain tissue generated from cells of people with Alpers disease—to model the disease and test NR as an intervention.⁹ After two months of NR treatment, the organoids showed a partial reversal of the disease presentation, including improved cortical structure, increased neuronal markers, reduced astrogliosis (a marker of brain tissue stress and injury), and upregulation of mitochondrial and synaptic pathways.

The authors of this research identified NR as a viable therapeutic candidate for Alpers disease, noting its potential relevance to other mitochondrial diseases, as well. Although this is only preclinical research at this point, the use of patient-derived brain organoids that closely mirror human brain biology makes these findings particularly meaningful. 

Ataxia-Telangiectasia

Ataxia-telangiectasia (AT) is a rare, inherited neurodegenerative disorder caused by mutations in the ATM gene, a master regulator of the DNA damage response. AT typically emerges in early childhood, with children typically developing early-onset cerebellar ataxia (unsteady gait and coordination problems), telangiectasias (small dilated blood vessels, especially in the eyes and skin), tremors, immunodeficiency, and a markedly increased risk of cancer. The disease is progressive and life-limiting, and there is currently no approved therapy that slows its underlying neurodegeneration. 

Loss of ATM function doesn’t just impair DNA repair; it also disrupts mitochondrial function and mitophagy, driving elevated oxidative stress and NAD+ depletion.¹⁰ In a cross-species preclinical study, NAD+ replenishment in AT models—including in neurons, mice, and worms—reduced PARP overactivation, improved mitochondrial quality control, normalized neuromuscular function, and extended lifespan, with benefits tied to both enhanced DNA repair and restored mitophagy.¹¹ Building on these results, an open-label, four‑month clinical study in 24 individuals with AT found that NR was well tolerated and linked to improvements in ataxia scores and increased serum IgG in immunodeficient patients, with benefits fading after NR withdrawal.¹² A subsequent two‑year, single‑arm study reported sustained increases in whole-blood NAD+ and improved motor coordination and eye movements in most participants.¹³ 

Due to this accumulating clinical data, an oral formulation of nicotinamide riboside chloride (NRCl) has received Orphan Drug and Rare Pediatric Disease designations from the U.S. Food and Drug Administration (USFDA) for use in AT, signaling regulatory recognition that targeting NAD+ metabolism may hold therapeutic promise for this otherwise treatment‑limited condition.

Barth Syndrome

Barth syndrome is an X-linked mitochondrial disorder, meaning it occurs almost exclusively in males. It’s caused by mutations in the TAFAZZIN (TAZ) gene, which encodes a protein needed to remodel cardiolipin, a phospholipid that supports mitochondrial membrane structure and electron transport chain function. Barth syndrome leads to symptoms like cardiomyopathy (enlarged or thickened heart muscle), skeletal muscle weakness, exercise intolerance, growth delay, and an abnormally low level of neutrophils with recurrent infections. These characteristics reflect the high energy demands of the heart and skeletal muscle, which are especially vulnerable when ATP production is impaired.

As cardiolipin remodeling is central to mitochondrial function, Barth syndrome is tightly linked to disrupted cellular energy metabolism and NAD+ biology. In a fruit fly model of Barth syndrome, supplemental NR restored exercise capacity and mitochondrial respiration, and increased mitochondrial DNA copy number and cardiolipin content.¹⁴ Another preclinical study introduced the TAZ mutation into 10 different fruit fly genetic backgrounds and found that, while NR frequently improved endurance and mitochondrial respiration, the magnitude of the benefit varied widely.¹⁵ These results suggest both therapeutic potential for NAD+ precursors in Barth syndrome and that individual genetics are likely to shape who responds and how strongly.

Cockayne Syndrome

Cockayne syndrome is a rare, autosomal recessive DNA repair disorder caused by mutations in the CSA (ERCC8) or CSB (ERCC6) genes, which help cells detect and repair everyday DNA damage. These mutations make cells unusually sensitive to ultraviolet (UV) light, driving photosensitivity and many signs of premature aging. Other characteristics include growth failure, sunken eyes, a beaked nose, prominent ears, microcephaly, hearing and vision loss, progressive neurodegeneration, and often early mortality.

At the cellular level, Cockayne syndrome is characterized by persistent DNA damage, PARP overactivation, reduced NAD+ levels, and mitochondrial dysfunction.¹⁶ A landmark preclinical study found that boosting NAD+—either through NR, PARP inhibition to preserve NAD+, or a high-fat diet that increased ketone bodies—activated SIRT1 and reversed several premature aging features in Cockayne syndrome mice, nematodes, and human cells.¹⁷

Later work demonstrated that short-term NR treatment in Cockayne syndrome mouse models prevented early hearing loss, restored outer hair cells, improved cochlear health, and rescued synaptic ribbon defects in the inner ear.¹⁸ Together, these studies have positioned Cockayne syndrome as one of the most compelling proof-of-concept cases for using NAD+ restoration therapy to meaningfully counteract the downstream effects of a DNA repair-driven disorder. 

Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a severe, X‑linked neuromuscular disease caused by mutations in the DMD gene, which encodes dystrophin, a structural protein that helps stabilize muscle cell membranes. Presenting in boys most often between ages 3 and 6, DMD can cause delayed motor milestones, difficulty running or jumping, calf enlargement, and progressive weakness that leads to loss of ambulation in adolescence, followed by cardiomyopathy and respiratory failure in early adulthood.

On a molecular level, dystrophin loss leads to repeated membrane damage, chronic inflammation, and mitochondrial dysfunction, which, in turn, overactivates PARPs and depletes NAD+.¹⁹ In a translational study, researchers found that DMD patient muscle biopsies showed increased expression of PARP family members and other NAD‑consuming enzymes, while a DMD mouse model had depleted muscle NAD+ levels.²⁰ Dietary NR replenished NAD+, improved muscle and cardiac structure, and reduced inflammation and fibrosis in these animals.

However, the overall picture in DMD is not straightforward, with other research showing that nutraceutical and pharmaceutical “cocktails” containing NR and other compounds did not significantly improve muscle function or histology in a more severe DMD mouse model.²¹ Others found that using NAD+ replacement strategies, including NR, raised NAD+ but failed to provide meaningful protection in dystrophin-deficient muscle.²² Taken together, these findings suggest that, while NAD+ depletion and PARP activation are clearly involved in DMD pathology, restoring NAD+ alone with precursors may not be sufficient as a standalone therapy for this disorder.

Friedreich’s Ataxia

Friedreich’s ataxia (FA) is a rare, inherited, progressive neuromuscular disease caused by a GAA repeat expansion in the FXN gene that silences frataxin, a mitochondrial protein essential for iron-sulfur cluster assembly—which is needed for healthy cellular energy metabolism—as well as iron homeostasis and oxidative stress defense. When frataxin is insufficient, iron accumulates in the mitochondria, generating damaging free radicals and leading to progressive mitochondrial dysfunction.²³ FA typically presents in adolescence with progressive loss of balance and coordination (ataxia), muscle weakness, cardiomyopathy, diabetes, loss of reflexes, and scoliosis. Although it’s the most prevalent inherited ataxia, only one FDA-approved therapy exists.²⁴

The NAD-FA connection runs through the frataxin-depleted heart and muscle, where mitochondrial dysfunction depletes NAD+ and impairs sirtuin-regulated metabolism.²⁵ In a preclinical study using a cardiac-specific frataxin knockout mouse model, NMN supplementation restored cardiac function to near-normal levels and improved mitochondrial energy metabolism, with effects that depended on the activation of SIRT3, an NAD-dependent enzyme that regulates mitochondrial health.²⁶ 

Building on these results, a phase 2 randomized controlled study enrolled 66 children and adults with FA across four groups: placebo, NR alone, exercise alone, or NR plus exercise.²⁷ After 12 weeks, the researchers found that the combination of NR plus exercise significantly improved peak aerobic capacity (VO₂ peak), suggesting that this approach may be a meaningful strategy for addressing the cardiopulmonary deficits in FA.

Hutchinson-Gilford Progeria Syndrome

Hutchinson-Gilford Progeria Syndrome (HGPS) is an exceptionally rare genetic disorder caused by a mutation in the LMNA gene that leads to the accumulation of a protein called progerin in cell nuclei, triggering dramatically accelerated aging.²⁸ Signs of HGPS typically appear within the first two years of life and include growth failure, loss of body fat, alopecia, stiff joints, and skin changes. However, the most life-threatening consequence is severe, early-onset cardiovascular disease, often leading to early death in the mid-teen years. 

At the cellular level, progerin accumulation leads to nuclear instability, impaired DNA repair, mitochondrial dysfunction, and oxidative stress—another pattern that closely mirrors cellular aging.²⁹ In a preclinical study, NMN supplementation in patient-derived HGPS stem cells enhanced NAD+ biosynthesis, restored mitochondrial function, reduced DNA damage, and mitigated oxidative stress.³⁰ Similarly, in an HGPS mouse model, four months of NMN treatment led to improvements in cardiovascular parameters, skin pathology, and gonadal function, as well as an extended lifespan, positioning NMN as a potential therapeutic candidate for this rare yet fatal condition.

Leigh Syndrome

Leigh syndrome is an inherited mitochondrial disease that typically arises in infancy or early childhood and primarily affects the brainstem and basal ganglia—an area associated with motor control.³¹ This disorder is caused by pathogenic variants in mitochondrial or nuclear genes that disrupt oxidative phosphorylation (most often Complex I), leading to developmental regression, muscle weakness, seizures, breathing difficulties, and, in many cases, death in childhood.

Because many forms of Leigh syndrome involve defects in Complex I—the main entry point for NADH into the electron transport chain—ATP production and the NAD+/NADH redox balance are impaired. In a preclinical study, researchers found that in mouse models of Leigh syndrome, both NAD+ levels and the NAD/NADH ratio were reduced—and that supplementing with NMN partially corrected this imbalance in the muscles and heart, improved cardiac function, and extended lifespan.³² Another study found that in Leigh syndrome models, Complex I defects lowered cellular NAD+ and damaged both heart and brain cells, while NR treatment helped restore NAD+ balance, improved heart rhythm and pumping function, and reduced signs of brain cell stress and damage.³³

Mitochondrial Myopathy

Mitochondrial myopathy is a form of mitochondrial disease that primarily affects skeletal muscle, causing exercise intolerance, muscle weakness, and fatigue. It often coexists with other multi‑system features such as progressive external ophthalmoplegia in adults, a condition in which weakness of the eye muscles leads to drooping eyelids and restricted eye movements.³⁴ Like other mitochondrial diseases, it can result from pathogenic variants in either mitochondrial DNA or nuclear genes that impair oxidative phosphorylation.

Although mitochondrial diseases present with enormous clinical variability—making them among the most difficult of rare diseases to treat—a unifying feature is that they tend to affect the high energy-demanding tissues like the heart, brain, and muscles first.³⁵ These defects disturb mitochondrial ATP production and the NAD+/NADH redox balance, and systemic NAD+ deficiency has been documented in adult‑onset mitochondrial myopathy.³⁶

In a mouse model of mitochondrial myopathy, oral NR was found to raise NAD+ levels, stimulate mitochondrial biogenesis, preserve muscle mitochondrial structure, and significantly delay disease progression,³⁷ while clinical research has shown similar benefits in humans. In a clinical study in patients with adult-onset mitochondrial myopathy, high-dose niacin corrected systemic NAD+ deficiency, increased muscle mitochondrial content and oxidative capacity, and improved muscle performance, supporting the idea that NAD+ repletion can partially restore muscle function in this disorder.³⁶

Werner’s Syndrome

Werner’s syndrome is a rare autosomal recessive progeroid disorder caused by loss‑of‑function mutations in the WRN DNA helicase, leading to genomic instability and mitochondrial dysfunction.³⁸ A leading characteristic of Werner’s syndrome is premature aging beginning in the 20s and 30s, including early graying and loss of hair, cataracts, diabetes, atherosclerosis, skin ulcers, and increased cancer and cardiovascular risk.³⁸ Both patient samples and model systems of Werner’s syndrome show impaired mitophagy and depletion of NAD+,³⁹ suggesting that disrupted NAD+ metabolism and mitochondrial quality control are key drivers of the premature aging phenotype in this condition.

Preclinical work has demonstrated that boosting NAD+ in Werner syndrome worm and fruit fly models, as well as in human cell lines, restored NAD+ levels, normalized mitophagy, improved mitochondrial function, extended lifespan, and delayed aging-like features.³⁹ In Werner’s syndrome patients, a double-blind randomized crossover study of NR was found to safely increase blood NAD+ and improve clinical markers, including arterial stiffness, skin ulcer burden, and kidney function, supporting NAD+ repletion as a promising therapeutic strategy in this disorder.⁴⁰

Xeroderma Pigmentosum

Xeroderma pigmentosum (XP), particularly the XPA subtype, is a rare autosomal recessive DNA repair disorder caused by defects in nucleotide excision repair, leading to extreme sensitivity to UV light and a dramatically increased risk of early‑onset skin cancers. Affected children develop severe sunburns after minimal sun exposure, as well as early freckling and pigment changes on sun‑exposed skin, ocular involvement, and, in some cases, progressive neurodegeneration with hearing loss, ataxia, and cognitive decline.

Preclinical research has shown that XPA is also associated with mitochondrial dysfunction, PARP1 hyperactivation, and depletion of cellular NAD+, which impairs SIRT1 activity and mitophagy in neurons.⁴¹ The study found that inhibiting PARP1 or replenishing NAD+ in XPA models restored NAD+ levels, reactivated SIRT1, normalized mitophagy, improved mitochondrial function, and prevented neurodegeneration in mice, suggesting that targeting NAD+ metabolism could modify disease progression in this DNA repair disorder.

Conclusion: NAD+ Therapy for Orphan Diseases: What the Research Says and What Comes Next

Despite being different conditions affecting different genes and different organs, all of these rare orphan diseases converge on a similar downstream crisis of mitochondrial dysfunction, cellular aging, oxidative stress, defective DNA repair, and NAD+ depletion. At the same time, conflicting data in Duchenne muscular dystrophy models—where some NAD+ repletion strategies improve muscle function while others fail to deliver durable benefit—underscore that NAD+ biology is not the whole story in every case and will likely be one component of a broader, combination therapeutic approach rather than a stand‑alone cure. 

Overall, the available human data is still early but increasingly encouraging: NR improves clinical markers and NAD+ levels in Werner’s syndrome and ataxia‑telangiectasia, NR plus exercise enhances cardiopulmonary fitness in Friedreich’s ataxia, and high‑dose niacin in adult‑onset mitochondrial myopathy normalizes systemic NAD+ and measurably improves muscle performance—currently the most robust clinical signal in this space. These orphan diseases offer an accelerated window into aging biology and mitochondrial decline that is likely to inform medicine far beyond rare disease, and repurposable, mechanism‑driven interventions such as NAD+ augmentation represent an unusually efficient, scalable opportunity in an area where traditional drug development resources have lagged behind the collective burden of patients.

An important consideration is that many clinical studies with NR have shown it is safe in humans, including some of these vulnerable diseases. Very few, if any, side effects have been reported. It is very important to treat orphan diseases with safe interventions, as they may need to take this for many years and represent a fragile portion of the population.

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