Congenital Vertebral-Cardiac-Renal Anomalies Syndrome

1. Disease Information

Overview. Congenital Vertebral-Cardiac-Renal Anomalies Syndrome is the Orphanet/MONDO name for a rare, genetically heterogeneous, autosomal recessive multiple-congenital-anomaly disorder caused by biallelic loss-of-function variants in the de novo NAD⁺ (nicotinamide adenine dinucleotide) biosynthesis pathway. The umbrella clinical/molecular entity is now widely referred to in the literature as Congenital NAD Deficiency Disorder (CNDD) — a name adopted after the causal mechanism was discovered in 2017. CNDD is genetically heterogeneous, comprising three OMIM-numbered subtypes distinguished by which pathway enzyme is disrupted:

Notably, the specific Orphanet/MONDO entity named "Congenital vertebral-cardiac-renal anomalies syndrome" (ORPHA:521438; also indexed as MONDO_0020831 on Open Targets) is described with the severe, infancy-lethal phenotype (hypoplastic/absent left ventricle, transposition of the great arteries, absent pulmonary trunk, hypoplastic/absent kidneys) that corresponds most closely to VCRL3/NADSYN1 (OMIM #618845), while the broader GeneReviews chapter "Congenital NAD Deficiency Disorder" (NBK593504) treats all three genes (HAAO/KYNU/NADSYN1) as one clinically overlapping spectrum. Curators should be aware of this granularity mismatch: the named "vertebral-cardiac-renal anomalies syndrome" label leans toward the NADSYN1-associated, most-severe end of the CNDD spectrum, but shares identical mechanism, evidence base, and management guidance with the HAAO- and KYNU-associated forms.

Key identifiers: - OMIM: #617660 (VCRL1/HAAO), #617661 (VCRL2/KYNU), #618845 (VCRL3/NADSYN1) - Orphanet: ORPHA:521438 - MONDO: MONDO:0020831 (per Open Targets); the term is also cataloged as MONDO:0030077 in some secondary listings — verify against the live MONDO release before binding - GARD (NCATS/NIH): Disease ID 17961 - GeneReviews: NBK593504 ("Congenital NAD Deficiency Disorder") - MedGen Concept IDs: C4540004 (VCRL1), C4540014 (VCRL2), C5394250 (VCRL3) - Gene OMIM (*): HAAO 604521; KYNU 605197; NADSYN1 608285

Synonyms: VCRL syndrome; Vertebral, Cardiac, Renal, and Limb Defects syndrome (1/2/3); Congenital NAD Deficiency Disorder (CNDD); HAAO-related / KYNU-related / NADSYN1-related multiple congenital anomaly syndrome; historically overlaps in the literature with "VACTERL-like association of genetic cause."

Source of information: Nearly all clinical knowledge derives from aggregated disease-level resources — case series and cohort reviews assembled from published case reports (OMIM, GeneReviews, Orphanet) rather than large prospective EHR cohorts, reflecting the rarity of the condition (GeneReviews July 2023 update: 27 reported individuals from 25 families worldwide, of whom 16 were living at time of publication).

2. Etiology

Disease causal factors — genetic. CNDD is caused by biallelic (homozygous or compound heterozygous) loss-of-function variants in one of three non-redundant genes encoding sequential enzymes of the de novo NAD⁺ synthesis pathway from dietary tryptophan: HAAO, KYNU, and NADSYN1. The founding paper, Shi et al. 2017 (PMID: 28792876, N Engl J Med 377:544–552), identified "variants … in two genes encoding enzymes of the kynurenine pathway, HAAO … and KYNU … Three patients carried homozygous variants predicting loss-of-function changes in the HAAO or KYNU proteins (HAAO p.D162, HAAO p.W186, or KYNU p.V57Efs21)," and reported that "the patients had reduced levels of circulating NAD." NADSYN1 was subsequently established as a third causal gene by Szot et al. 2020 (PMID: 31883644, Am J Hum Genet 106:129–136), describing five individuals from four families with biallelic NADSYN1* variants and phenotypes "rang[ing] from the isolated absence of both kidneys to multiple malformations of the vertebrae, heart, limbs, and kidney," with "no affected individual surviv[ing] for more than three months postnatally" in that severe cohort.

Risk factors: - Genetic: Biallelic pathogenic/likely pathogenic variants in HAAO, KYNU, or NADSYN1 (per ACMG/AMP criteria, Richards et al. 2015, PMID: 25741868) are causal, not merely a risk factor — the disorder is fully penetrant when both alleles are null. Parental consanguinity substantially raises a priori risk in any autosomal recessive disorder; multiple reported families are consanguineous. A maternal chromosome 2 isodisomy (uniparental disomy) unmasking a homozygous KYNU exon-5 deletion has been documented as a distinct mechanism producing biallelic loss-of-function from a single carrier parent (Schüle et al. 2021, PMID: 34200361, Genes 12:879, "A Homozygous Deletion of Exon 5 of KYNU Resulting from a Maternal Chromosome 2 Isodisomy … Causes Catel-Manzke-Syndrome/VCRL Syndrome"). - Environmental / maternal metabolic: Because the terminal metabolite is the same essential cofactor (NAD⁺) required in the mother's own developing embryo, maternal dietary niacin/tryptophan insufficiency, and possibly maternal illness or drugs (e.g., isoniazid, which depletes vitamin B6 needed for kynurenine-pathway flux) that impair the mother's own NAD⁺ supply during the periconceptional/early-embryonic window, are hypothesized modifiers of severity and penetrance in genetically at-risk pregnancies, based on the mouse model data below (Shi et al. 2017).

Protective factors: - Genetic: No protective alleles are established; heterozygous carriers of HAAO/KYNU/NADSYN1 variants are asymptomatic. - Environmental — niacin/nicotinamide supplementation. This is the single most important modifiable factor identified for this disease class. Shi et al. 2017 showed in Haao-null and Kynu-null mouse embryos that malformations mirroring the human phenotype occur "owing to NAD deficiency," and that "niacin supplementation during gestation prevented the malformations in mice." Follow-on commentary (e.g., coverage of the Dunwoodie group's work, Victor Chang Cardiac Research Institute) proposed maternal supplementation strategies (in the range of ~140 mg/day investigated preclinically — roughly 10× the standard RDA for women) as a plausible clinical prevention strategy, though this has not yet been validated in a human interventional trial for genetically confirmed carrier couples. A broader systematic review/meta-analysis of maternal dietary niacin intake and congenital anomalies (PMID: 34748060) supports a population-level association between niacin status and malformation risk.

Gene-environment interactions. The core G×E model of this disease is that haploinsufficient/heterozygous carrier status combines with maternal NAD⁺-precursor insufficiency (low dietary tryptophan/niacin, malabsorption, or drugs interfering with kynurenine-pathway flux) to push total embryonic NAD⁺ below a mechanistic threshold during the vulnerable early-organogenesis window — while frank biallelic loss-of-function in the embryo itself produces a much larger, largely non-nutrition-rescuable NAD⁺ deficit. Mark 2022 (PMID: 35484986, Am J Med Genet A 188:2834–2849, "NAD+ deficiency in human congenital malformations and miscarriage: a new model of pleiotropy") proposes that this G×E axis underlies a wider group of overlapping malformation syndromes (VACTERL association, limb-body wall complex, pentalogy of Cantrell, OEIS complex, oculoauriculovertebral spectrum, MURCS, sirenomelia, urorectal septum malformation sequence) and recurrent miscarriage, framing NAD⁺ deficiency as a pleiotropic developmental mechanism rather than a single-syndrome cause.

3. Phenotypes

Phenotype frequencies below are drawn from the GeneReviews CNDD cohort synthesis (25–27 reported affected individuals; NBK593504, 2023 update) and the founding case series.

Onset: All features are congenital/present at birth or detected prenatally by ultrasound; severity spans a spectrum from prenatal loss/termination to survival into adulthood (oldest reported living patient: age 30, Erbs et al. 2023, PMID: 36649848). Progression: structural anomalies are static congenital malformations rather than progressive; secondary sequelae (e.g., chronic kidney disease from renal hypoplasia, scoliosis progression, hearing loss impact) can evolve postnatally and require longitudinal surveillance. Quality of life impact: driven mainly by the combination of congenital heart disease, renal insufficiency, developmental/intellectual disability, and orthopedic complications; no disease-specific QoL instrument has been published, but impact is analogous to other multi-system congenital anomaly syndromes requiring lifelong multidisciplinary care.

4. Genetic/Molecular Information

Causal genes (all three are non-redundant, sequential enzymes of the de novo NAD⁺ pathway):

Variant classification and type. Reported variants span nonsense (e.g., HAAO p.D162, p.W186), frameshift (KYNU p.V57Efs21), splice-site, missense (NADSYN1 p.A573T), and structural/copy-number variants (a homozygous KYNU exon-5 deletion via maternal isodisomy). All disease-causing genotypes are biallelic loss-of-function or severely hypomorphic, consistent with a straightforward loss-of-function* mechanism (no dominant-negative or gain-of-function alleles reported). ACMG/AMP criteria (PMID: 25741868) are the standard classification framework applied in the primary literature (all reported variants pathogenic/likely pathogenic).

Population allele frequency: Individual causal variants are, as expected for an ultra-rare autosomal recessive disorder, absent or present only as very rare heterozygous alleles in gnomAD; no common founder variant has been reported across the described families (each family typically carries a private variant), though the maternal UPD2 case represents a distinct, non-Mendelian recurrence mechanism.

Somatic vs. germline: Exclusively germline — this is a developmental/Mendelian disorder, not a somatic/cancer-related condition.

Functional consequences: Uniform loss of enzymatic function, verified in several studies by in vitro expression assays showing "essentially abolished" enzyme activity for KYNU truncating alleles, and confirmed physiologically by reduced circulating NAD⁺ and accumulation of upstream pathway metabolites (3-hydroxyanthranilic acid [3HAA] elevated / NAD(H) reduced for HAAO; 3-hydroxykynurenine [3HK] elevated / NAD(H) reduced for KYNU).

Modifier genes: None formally established; phenotypic variability within and across families (even with identical genotypes) suggests unidentified genetic or environmental (maternal nutritional) modifiers, consistent with the mouse data showing rescue by maternal dietary niacin.

Epigenetic information: Not established as a primary mechanism for this disorder; NAD⁺ itself is a cofactor for epigenetic enzymes (sirtuins, PARPs), so downstream epigenetic dysregulation is mechanistically plausible but not directly documented in patient tissue to date.

Chromosomal abnormalities: Not a chromosomal/copy-number syndrome per se, though the KYNU exon-5 deletion via maternal isodisomy of chromosome 2 (Schüle et al. 2021) is a structural mechanism worth noting for differential/recurrence-risk counseling.

Genetically related (allelic) disorders (per GeneReviews): - HAAO: no other associated phenotype reported. - KYNU: biallelic variants can also cause isolated hydroxykynureninuria (xanthurenic aciduria) — a biochemical excretory phenotype without the full malformation syndrome — indicating allelic/dosage heterogeneity. - NADSYN1: preliminary evidence (Lin et al. 2021, PMID: 34681008) suggests monoallelic variants may be associated with a milder spectrum of vertebral/cardiac/renal/limb/hepatic defects and intraspinal anomalies, though this requires confirmation.

Suggested GO terms for pathway annotation: - GO:0034354 — "NAD biosynthesis via nicotinamide riboside salvage pathway" (salvage, contrast pathway) - GO:0009435 — "NAD biosynthetic process" (parent term covering the de novo route) - GO:0043420 — "anthranilate metabolic process" - GO:0019805 — "quinolinate biosynthetic process" (product of the HAAO reaction, immediate NAD⁺ precursor) - GO:0033721 — "3-hydroxyanthranilate 3,4-dioxygenase activity" (HAAO molecular function) - GO:0030429 — "kynureninase activity" (KYNU molecular function) - GO:0008795 — "NAD+ synthase activity" (NADSYN1 molecular function)

5. Environmental Information

Environmental factors: The dominant environmental modifier for this specific gene-driven disorder is maternal NAD⁺-precursor (niacin/tryptophan) nutritional status during the periconceptional and early-embryonic period, as established mechanistically in the Shi et al. 2017 mouse model. This is distinct from a classical toxin-exposure etiology — the "environmental" axis here operates through nutrient sufficiency for a genetically compromised biosynthetic pathway rather than through an exogenous toxicant.

Lifestyle factors: Maternal diet quality/adequacy of niacin (vitamin B3) and tryptophan intake is the principal modifiable lifestyle factor implicated; standard prenatal multivitamins in most jurisdictions do not include niacin at the doses studied preclinically (~140 mg/day, ~10× US RDA for women), so this is an area of active clinical translation rather than settled guideline recommendation.

Infectious agents: None implicated; this is a purely genetic/metabolic developmental disorder with no known infectious trigger.

Drug/xenobiotic interactions (plausible, not disease-specific evidence): Agents that deplete vitamin B6 (a cofactor for kynurenine-pathway enzymes upstream of HAAO/KYNU, e.g., isoniazid) or otherwise impair tryptophan/kynurenine-pathway flux are biologically plausible aggravating exposures in a genetically at-risk pregnancy, based on pathway biology, though disease-specific human data linking a named xenobiotic exposure to CNDD severity have not been published.

6. Mechanism / Pathophysiology

Causal chain (numbered, from initiating lesion to clinical manifestation):

1. Biallelic loss-of-function variants in HAAO, KYNU, or NADSYN1 each abolish or severely reduce the catalytic activity of a sequential enzyme in the de novo NAD⁺ biosynthesis pathway that converts dietary tryptophan → kynurenine → 3-hydroxykynurenine → 3-hydroxyanthranilic acid (HAAO substrate) → quinolinic acid → nicotinic acid adenine dinucleotide (NAAD) → NAD⁺ (NADSYN1's product) — directly demonstrated by loss of enzymatic activity in expression assays (Shi et al. 2017, PMID:28792876).
2. This leads to accumulation of the immediate upstream metabolite for each block (3HAA for HAAO deficiency; 3HK for KYNU deficiency) and a reduction in de novo–synthesized NAD⁺ — directly measured as reduced circulating NAD⁺/NADH in affected patients and in Haao-null/Kynu-null mouse embryos (demonstrated).
3. Because the salvage pathway cannot fully compensate during early embryogenesis (the bulk of adult cellular NAD⁺ is normally salvage-derived, but the embryo appears to rely disproportionately on de novo synthesis in a defined developmental window), this results in a critical, tissue-wide NAD⁺ deficit specifically during early organogenesis — inferred from the mouse rescue experiments and the stereotyped, organ-selective malformation pattern rather than directly visualized in human embryos (partly inferred).
4. NAD⁺ deficiency impairs core NAD⁺-dependent cellular processes required for organogenesis, including its role as an electron acceptor for ATP synthesis (oxidative phosphorylation/glycolysis), and as a substrate for NAD⁺-consuming enzymes (sirtuins, PARPs, cADPR synthases) that regulate chromatin state, DNA-damage response, and cell signaling — this leads to disrupted proliferation, differentiation, and patterning signals in the developing mesoderm-derived organ primordia (largely inferred from general NAD⁺ biology; not yet organ-specifically dissected in this disease).
5. Because heart, kidney, and vertebral column all arise from tightly time-linked mesodermal developmental programs active in the same early post-gastrulation window, this results in the disease's signature co-occurring triad of cardiac, renal, and vertebral malformation, with limb, craniofacial, and neurodevelopmental structures affected to a variable, generally lesser degree depending on the residual NAD⁺ level (dose-dependent severity — supported by the genotype-severity gradient across HAAO/KYNU vs. the more severe NADSYN1/VCRL3 cohort).
6. In the most severe cases (particularly biallelic NADSYN1 loss), this leads to profound structural cardiac defects (hypoplastic/absent left ventricle, transposition of the great arteries, absent pulmonary trunk) and bilateral renal agenesis/hypoplasia incompatible with postnatal survival — resulting in pregnancy loss or death within the first year of life (demonstrated clinically; Szot et al. 2020).
7. In milder allelic combinations (partial residual enzyme activity), this results in the broader, non-lethal CNDD phenotypic spectrum — short stature, isolated or combined vertebral/cardiac/renal/limb anomalies, developmental delay, and hearing loss — with survival into childhood and, in the mildest known case, adulthood (demonstrated).
8. Restoring embryonic NAD⁺ supply via maternal dietary niacin supplementation during gestation bypasses the enzymatic block (niacin enters NAD⁺ synthesis through the separate Preiss-Handler pathway, independent of HAAO/KYNU/NADSYN1) and prevents the malformation cascade in Haao-null and Kynu-null mouse embryos — demonstrated experimentally and the strongest direct mechanistic proof of the causal chain (Shi et al. 2017).

Molecular pathways: Kynurenine pathway / tryptophan catabolism (KEGG: hsa00380 Tryptophan metabolism); de novo NAD⁺ biosynthesis pathway (KEGG: hsa00760 Nicotinate and nicotinamide metabolism; Reactome: "Tryptophan catabolism"). No canonical developmental signaling pathway (Wnt/MAPK/mTOR) has been shown to be the direct downstream effector — the current model treats NAD⁺ depletion itself, and its downstream effects on ATP generation and NAD⁺-dependent enzymes, as the proximate lesion (Dunwoodie et al. 2023 review, "Nicotinamide Adenine Dinucleotide Deficiency and Its Impact on Mammalian Development," Antioxid Redox Signal, doi:10.1089/ars.2023.0349, is the most current mechanistic synthesis).

Cellular processes: Impaired cellular bioenergetics (ATP synthesis) and NAD⁺-dependent enzymatic signaling (sirtuin-mediated deacetylation, PARP-mediated DNA repair) in rapidly proliferating embryonic mesodermal progenitors during organogenesis are the leading hypothesized cellular mechanisms; oxidative stress has also been proposed as a downstream consequence of impaired NAD⁺/NADH redox balance.

Protein dysfunction: Straightforward loss of enzymatic function (not misfolding/aggregation) for HAAO, KYNU, and NADSYN1 — nonsense, frameshift, and splice variants predominate, consistent with a null mechanism; the one recurrent missense allele (NADSYN1 p.A573T) has been functionally shown to impair NAD⁺ synthetase activity in vitro.

Metabolic changes: Central to this disease — this is fundamentally a tryptophan/NAD⁺ pathway metabolic disorder. Biochemically diagnostic findings include elevated upstream metabolites (3HAA in HAAO deficiency; 3HK, xanthurenic acid, kynurenine in KYNU deficiency) and reduced NAD⁺/NADH; a dedicated "metabolic signature" study for NADSYN1-associated disease has been published (PMC10866660) proposing a biochemical biomarker panel for diagnosis/monitoring.

Advanced/omics technologies: A 2025 preprint/publication (Dunwoodie group, bioRxiv 10.1101/2025.01.10.632366; PMID: 39829932) establishes a zebrafish model of NAD⁺ deficiency-derived congenital disorders, extending the mouse data and explicitly raising the hypothesis that CNDD and VACTERL association "possess similar underlying causes," while noting that "the mechanism by which NAD⁺ deficiency causes CNDD developmental anomalies has not been determined" at the cellular/molecular signaling level — an open mechanistic gap appropriate to flag as a KNOWLEDGE_GAP or HUMAN_MODEL_MISMATCH discussion node in a KB entry (mouse/zebrafish recapitulate gross structural phenotype and confirm niacin rescue, but the precise cell-signaling explanation for organ selectivity remains undetermined).

Suggested GO (biological process) / CL (cell type) terms: GO:0009435 (NAD biosynthetic process), GO:0006979 (response to oxidative stress), GO:0006974 (cellular response to DNA damage stimulus, PARP-relevant); relevant cell types are broadly mesodermal cardiac progenitor cells (CL:0000499), metanephric mesenchyme/nephron progenitor cells (CL:1000384), and sclerotome-derived vertebral precursor cells — none of the primary literature has yet performed single-cell resolution of the affected embryonic compartments in this specific human disorder.

7. Anatomical Structures Affected

Organ level (primary): Heart (all major structural compartments — left ventricle, outflow tract, septa, valves), kidneys (parenchyma and collecting system), vertebral column (vertebral bodies, ribs). Secondary/associated: limbs (long bones, hands/feet), craniofacial skeleton and palate, inner ear, brain (microcephaly, hydrocephalus, cerebellar hypoplasia in a subset), thyroid and parathyroid glands, spleen (polysplenia), esophagus/trachea (TEF), eyes.

Body systems involved: Cardiovascular, renal/urinary, musculoskeletal (axial and appendicular), nervous (central and peripheral/hearing), endocrine, gastrointestinal, ophthalmologic, lymphatic (cystic hygroma).

Suggested UBERON terms: UBERON:0000948 (heart); UBERON:0002113 (kidney); UBERON:0002298 (vertebral column); UBERON:0002101 (limb); UBERON:0001456 (face); UBERON:0001690 (ear); UBERON:0000955 (brain); UBERON:0002046 (thyroid gland); UBERON:0001132 (parathyroid gland); UBERON:0002106 (spleen).

Tissue/cell level: Cardiac muscle and endocardial/outflow-tract mesenchyme; nephron epithelium and metanephric mesenchyme; sclerotome-derived vertebral chondro-osseous tissue; limb bud mesenchyme/chondrocytes. Cell Ontology suggestions: CL:0000746 (cardiac muscle cell), CL:0002518 (kidney epithelial cell), CL:0000138 (chondrocyte).

Subcellular level: Mitochondria (site of NAD⁺-dependent oxidative phosphorylation; GO:0005739) and nucleus (site of NAD⁺-dependent sirtuin/PARP chromatin and DNA-repair activity; GO:0005634) are the most mechanistically relevant compartments, given NAD⁺'s dual roles as a redox cofactor and enzymatic substrate.

Localization/laterality: Renal involvement can be unilateral (agenesis in 6 cases) or bilateral; cardiac and vertebral anomalies are generally midline/structural rather than strictly lateralized; limb involvement, when present, is typically bilateral and symmetric (consistent with a systemic metabolic rather than a focal teratogenic insult).

8. Temporal Development

Onset: Congenital — all structural anomalies originate during embryonic organogenesis (roughly weeks 3–8 post-conception for the heart, kidney, and vertebral primordia), detectable prenatally by ultrasound in many cases and at birth in others. This is a true prenatal-onset disorder; there is no pediatric/adult-onset variant.

Progression: The structural malformations themselves are static (fixed at the point of embryogenesis), but their functional consequences progress postnatally — e.g., renal hypoplasia can evolve into progressive chronic kidney disease, scoliosis from vertebral segmentation defects can worsen through skeletal growth, and developmental delay/intellectual disability trajectories unfold through childhood. Disease course is therefore best described as a stable structural lesion with a progressive secondary functional burden.

Disease stages: No formal staging system exists; clinical severity is best stratified by genotype/residual enzyme activity, ranging from prenatal lethality (most severe NADSYN1 cases) to survival into adulthood (mildest reported cases, oldest known patient age 30).

Course pattern: Non-relapsing, non-remitting — a fixed congenital anomaly burden with the natural history of any structural birth-defect syndrome (i.e., defined by the severity of the initial malformations rather than an episodic or fluctuating pathobiology).

Critical period: Explicitly established mechanistically — the mouse rescue experiments (Shi et al. 2017) demonstrate that maternal niacin supplementation during gestation (i.e., during the embryonic organogenesis window) is sufficient to prevent malformation, defining early gestation as the critical intervention window for any future preventive strategy in genetically at-risk pregnancies.

9. Inheritance and Population

Epidemiology: Extremely rare — GeneReviews (2023) documents 27 reported affected individuals from 25 families worldwide across all three genes combined, almost certainly an underascertainment given likely underdiagnosis of stillbirths/terminations and phenotypic overlap with VACTERL association. No formal population prevalence or incidence estimate (per 100,000) has been published; the disorder should be classified as ultra-rare / cases-in-literature only for prevalence-banding purposes.

Inheritance pattern: Autosomal recessive for all three subtypes (HAAO/KYNU/NADSYN1). GeneReviews: "The diagnosis of CNDD is established in a proband with suggestive findings and biallelic pathogenic variants in HAAO, KYNU, or NADSYN1."

Penetrance: Essentially complete for biallelic null genotypes, based on the consistency of the malformation phenotype across reported families, though expressivity (see below) varies widely.

Expressivity: Markedly variable, even for identical genotypes within a family, ranging from isolated bilateral renal agenesis to the full multi-organ syndrome — reflecting the hypothesized gene-environment (maternal NAD⁺ precursor sufficiency) interaction described in Section 2.

Genetic anticipation: Not applicable/not reported (mechanism is enzymatic loss-of-function, not a repeat-expansion disorder).

Germline mosaicism: Not directly documented but should be considered in recurrence-risk counseling per general AR-disorder practice; the GeneReviews chapter recommends confirmatory parental testing partly to exclude occult mosaicism/de novo scenarios.

Founder effects: No population-specific founder variant has been established; each reported family generally carries a private variant.

Consanguinity: A recognized risk factor, as for any rare autosomal recessive disorder; several reported families are consanguineous.

Carrier frequency: Not established (too rare for population carrier-frequency databases such as gnomAD to yield a meaningful estimate for any single pathogenic allele).

Population demographics: No ethnic, geographic, or sex-specific enrichment has been reported; cases have been described across multiple continents/ancestries in the literature (North America, Europe, Australia most represented, reflecting the discovering research groups' referral bases rather than a true epidemiological signal). No male:female skew is expected or reported for an autosomal recessive disorder.

Age distribution: By definition, congenital onset; postnatal survivors range from neonatal death (severe cases) to age 30 at last published report.

10. Diagnostics

Suggestive findings (GeneReviews): prenatal/postnatal imaging showing congenital heart defects (left- and/or right-sided), renal anomalies (aplasia/hypoplasia/dysplasia), vertebral anomalies (butterfly/hemi-/wedge/fused vertebrae), shortened long bones (rhizomelia/brachymelia), and short metacarpals with accessory ossicles; clinical findings of short stature, microcephaly, dysmorphic (cupped/low-set) ears, sensorineural hearing loss, nuchal redundancy/cystic hygroma, cutaneous syndactyly, hyperphalangism, developmental delay/ID, sacral dimple, clubfeet; and a compatible autosomal recessive family history (though its absence does not exclude the diagnosis).

Establishing the diagnosis: Biallelic pathogenic variants in HAAO, KYNU, or NADSYN1 confirmed by molecular genetic testing, via either: 1. A gene-targeted VACTERL-association multigene panel including HAAO, KYNU, NADSYN1 (sequence + deletion/duplication analysis), or 2. Exome or genome sequencing when the phenotype overlaps with other multiple-congenital-anomaly syndromes.

Biochemical/metabolomic testing (research/adjunct use): plasma/urine metabolite panels showing elevated upstream kynurenine-pathway intermediates (3HAA, 3HK, xanthurenic acid, kynurenine) and reduced NAD⁺/NADH; a dedicated NADSYN1 "metabolic signature" panel has been proposed (PMC10866660) as a functional confirmatory/monitoring tool alongside genetic testing.

Imaging: Fetal/postnatal echocardiography (cardiac defects), renal/bladder ultrasound (renal anomalies), spinal radiographs ± CT (vertebral segmentation), spinal ultrasound (<3 months) or MRI (>3 months) if dysraphism/tethered cord suspected, brain MRI if microcephaly/seizures/neuromuscular findings.

Differential diagnosis (GeneReviews, summarized): - VACTERL association — the closest clinical mimic; distinguished by CNDD's relative rarity of anal atresia and tracheoesophageal fistula, and its higher frequency of disproportionate short stature, developmental delay, and facial dysmorphism. Mechanistic overlap is now an active research question (see Section 6). - Townes-Brocks syndrome (SALL1, AD) — dysplastic/hearing-impaired ears and thumb malformations much more prominent; imperforate anus in ~84%. - Catel-Manzke syndrome (TGDS, AR) — distinctive hand malformation with accessory ossicles and index-finger shortening; Pierre Robin sequence more common, cardiac/vertebral/renal anomalies rarer. - Fanconi anemia (~23 genes, AR/AD/X-linked) — bone marrow failure and cancer predisposition absent in CNDD; structural anomaly rates markedly lower. - 22q11.2 deletion syndrome (AD) — immune deficiency and palatal anomalies far more prominent. - Teratogen-induced phenocopies: diabetic embryopathy, thalidomide embryopathy, and valproate embryopathy each share partial overlap but differ in the frequency/pattern of neural tube, cleft, and limb-reduction defects (van de Putte et al. 2020, PMID: 32596782, is the key comparative reference for the VACTERL differential specifically).

Screening: No population newborn-screening program exists (metabolite panel is not part of standard newborn screening); prenatal ultrasound is the practical first-line detection modality given the structural nature of the anomalies; carrier/prenatal/preimplantation genetic testing is available once a family's causal variants are identified.

11. Outcome/Prognosis

Survival/mortality: Highly genotype/severity-dependent. In the most severe cohort (biallelic NADSYN1, Szot et al. 2020), "no affected individual survived for more than three months postnatally," with outcomes spanning isolated bilateral renal agenesis to lethal multi-organ malformation. Across the full GeneReviews cohort of 27 individuals, 9 did not survive (5 pregnancy termination/loss, 4 deaths in the first year from severe structural defects), while 16 were living, including one individual reported alive at age 30 (Erbs et al. 2023) — demonstrating that survival to adulthood is possible with milder genotypes and modern multidisciplinary management.

Morbidity/function: Long-term morbidity is driven by chronic kidney disease (in survivors with significant renal hypoplasia), residual cardiac lesions requiring ongoing cardiology follow-up, orthopedic complications (scoliosis, limb-length discrepancy), sensorineural hearing loss, and variable intellectual disability/developmental delay (up to 62% in the reviewed cohort). No standardized disability or QoL instrument has yet been applied to this population in the literature.

Complications: Progressive chronic kidney disease/hypertension (renal survivors), tethered spinal cord (in those with spinal dysraphism), feeding/aspiration issues from TEF or laryngeal web, hypothyroidism/hypoparathyroidism, and — where polysplenia is present — functional asplenia/infection risk.

Recovery potential: Structural anomalies themselves are not reversible; outcome depends on surgical/medical correction of individual organ defects (cardiac surgery, orthopedic correction, hearing aids, etc.) rather than on treating the underlying metabolic lesion, since no NAD⁺-repletion treatment for affected individuals postnatally has yet been validated or recommended (see Section 12).

Prognostic factors: Genotype/gene (NADSYN1-associated disease trends more severe/lethal than HAAO- or KYNU-associated disease in the literature to date, though formal genotype-phenotype correlation is explicitly stated as unestablished by GeneReviews), severity and combination of organ involvement (cardiac + bilateral renal disease carries the worst prognosis), and gestational NAD⁺ status (maternal nutritional modifier, per the mouse model).

12. Treatment

No disease-modifying cure exists. Management is supportive and organ-specific, coordinated through a multidisciplinary genetics/cardiology/nephrology/orthopedics/developmental team, per GeneReviews (NBK593504):

• Congenital heart defects: Standard pediatric cardiology/cardiac surgical management per lesion type (NCIT:C15329, Surgical Procedure; NCIT:C49236, Therapeutic Procedure).
• Renal anomalies: Nephrology monitoring of function/blood pressure; avoid nephrotoxic agents in those with solitary/hypoplastic kidneys.
• Vertebral/orthopedic anomalies (scoliosis, clubfoot, limb anomalies): Standard orthopedic management (NCIT:C16186, Orthopedic Surgical Procedure); neurosurgical management if tethered cord.
• Cleft palate: Craniofacial team management.
• Hearing loss: Hearing aids/otolaryngology referral (NCIT device pattern applies).
• GI anomalies (TEF, pyloric stenosis, laryngeal web): Gastroenterology/otolaryngology surgical management.
• Polysplenia: Hematology/immunology monitoring for functional asplenia.
• Developmental delay/intellectual disability: Early intervention (0–3), developmental preschool, IEP/504 supports, physical/occupational/speech therapy, ABA for autism-spectrum features, developmental pediatrics.
• Seizures: Standard anti-seizure medication (no CNDD-specific agent shown superior).
• Endocrine (hypothyroidism, hypoparathyroidism): Standard endocrinology management/hormone replacement (NCIT:C15986, Pharmacotherapy).
• Ophthalmologic findings (strabismus, ptosis): Standard ophthalmologic management.
• Family/psychosocial: Genetic counseling, social work, palliative/home-nursing referral where indicated.

A notable and reportable gap: despite NAD⁺ deficiency being the established root mechanism, and despite gestational niacin supplementation preventing malformation in mouse models (Shi et al. 2017), the current GeneReviews chapter does not recommend niacin/nicotinamide/NAD⁺/NMN/NR supplementation as a treatment for affected individuals postnatally, and no human interventional trial of maternal or child NAD⁺-precursor supplementation for this specific disorder has been published as of the most recent literature reviewed. This is an important, explicit KNOWLEDGE_GAP for a KB mechanism entry: the mechanistic and preclinical rationale for prevention (pre-conception/gestational niacin supplementation in confirmed carrier couples) is strong, but translation into a validated treatment/prevention guideline for humans remains an active, unresolved research question.

Experimental/preclinical therapeutics: Gestational niacin supplementation is the sole experimentally validated intervention to date, demonstrated only in Haao-null/Kynu-null mouse embryos (Shi et al. 2017) and now being extended in the 2025 zebrafish CNDD model (PMID: 39829932) to further dissect the rescue mechanism. No registered clinical trial (ClinicalTrials.gov) specific to CNDD/VCRL syndrome niacin prophylaxis was identified in the sources reviewed.

Screening/counseling role of niacin data: Even absent a formal trial, the preclinical prevention data is directly relevant to genetic counseling for known carrier couples planning a subsequent pregnancy, and several review/commentary sources (Dunwoodie group publications and secondary press coverage) explicitly frame periconceptional niacin supplementation as a candidate primary-prevention strategy pending clinical validation.

13. Prevention

Primary prevention: The strongest candidate primary-prevention strategy is periconceptional/gestational niacin (vitamin B3) supplementation in couples known to carry pathogenic HAAO/KYNU/NADSYN1 variants, grounded directly in the mouse rescue data (Shi et al. 2017) — niacin enters the Preiss-Handler NAD⁺-synthesis pathway independently of the three affected de novo-pathway enzymes, restoring embryonic NAD⁺ sufficiency. This remains preclinically validated but not yet clinically proven or formally guideline-recommended in humans, and should be characterized in a KB entry as an emerging/hypothesis-level prevention strategy rather than an established standard of care.

Secondary prevention: Prenatal ultrasound surveillance in known at-risk pregnancies (both parents confirmed carriers) for early detection of cardiac, renal, and vertebral anomalies, enabling informed counseling about pregnancy management and coordinated perinatal/neonatal care planning.

Genetic counseling and reproductive options: Central to prevention in this AR disorder. GeneReviews recommends: confirming parental carrier status by molecular testing (also serving to distinguish true biparental inheritance from de novo variants, parental mosaicism, or uniparental disomy); offering carrier testing to reproductive partners of known carriers, especially where consanguinity is likely; and discussing prenatal diagnosis and preimplantation genetic testing (PGT) once the family's causal variants are known. For each pregnancy where both parents are confirmed carriers, recurrence risk is the standard AR figure: 25% affected, 50% carrier, 25% unaffected/non-carrier.

Public health/behavioral interventions: No population-level screening or public health program exists for this ultra-rare disorder; prevention efforts are necessarily family- and genetics-clinic-based rather than population-based.

Prophylaxis: As above, gestational niacin supplementation is the only biologically targeted prophylactic candidate under discussion in the literature, but is not yet an established prophylactic guideline.

14. Other Species / Natural Disease

Taxonomy of model organisms used: Mus musculus (NCBITaxon:10090) and Danio rerio (NCBITaxon:7955) — no naturally occurring veterinary/companion-animal disease analog has been reported in the literature reviewed (this is a laboratory-modeled human genetic disorder rather than a condition recognized in OMIA/veterinary case series).

Orthologous genes: Mouse Haao (MGI:1919711), Kynu (MGI ortholog), Nadsyn1 (MGI:1926164) are the direct murine orthologs used to generate the null-allele models; zebrafish orthologs (haao, kynu, nadsyn1) were used in the 2025 model.

Comparative biology: The kynurenine pathway and de novo NAD⁺ biosynthesis route are highly evolutionarily conserved from bacteria through vertebrates (noted explicitly in the KYNU/NAD-biosynthesis evolutionary literature), supporting cross-species mechanistic validity of the mouse and zebrafish models for this pathway, even though no spontaneous/natural veterinary disease counterpart is documented.

Zoonotic potential/transmission: Not applicable — this is a non-communicable genetic developmental disorder.

15. Model Organisms

Mouse (Mus musculus): - Genetic models: Haao-null and Kynu-null knockout mice (Shi et al. 2017, PMID: 28792876) are the foundational models establishing causality. - Phenotype recapitulation: Null mouse embryos develop malformations described as similar to those seen in affected human patients, attributed directly to embryonic NAD⁺ deficiency. - Key experimental result: Gestational niacin supplementation of null-mutant dams prevented malformations in their offspring — the single most important interventional proof-of-concept in the field, directly informing both mechanism (Section 6) and prevention hypotheses (Section 13). - Limitations: Mouse null models represent complete loss-of-function, which may not fully capture the phenotypic range seen with human hypomorphic/missense alleles (e.g., the milder NADSYN1 p.A573T genotype); litter-level variability and resorption patterns in these models have also been used (Mark 2022) to model human miscarriage risk, an extrapolation not yet directly validated in human tissue.

Zebrafish (Danio rerio): - A 2025 study (bioRxiv 10.1101/2025.01.10.632366; PMID: 39829932; also published in a peer-reviewed venue per ScienceDirect indexing) established the first zebrafish model of NAD⁺ deficiency-derived congenital disorders, targeting the same pathway genes, explicitly to further probe the unresolved question of why NAD⁺ deficiency selectively disrupts cardiac, renal, vertebral, and limb development and to test the hypothesis of shared mechanism with VACTERL association. - Applications: Zebrafish offer external embryonic development, rapid generation time, and amenability to high-throughput chemical/genetic screening — well suited to dissecting the still-open cell-signaling mechanism downstream of NAD⁺ depletion and to future compound (e.g., NAD⁺ precursor) screening.

Resources: MGI (Mouse Genome Informatics) for Haao/Kynu/Nadsyn1 mouse alleles; ZFIN for zebrafish CNDD-model lines as they become deposited; no dedicated patient-derived iPSC or organoid model of CNDD was identified in the literature reviewed, representing an additional experimental-model gap relative to many other monogenic disorders.

Summary Table: Key Evidence Citations

Sources

• congenital vertebral-cardiac-renal anomalies syndrome - NORD
• Vertebral, cardiac, renal, and limb defects syndrome 1 - MedGen
• Orphanet: Congenital vertebral-cardiac-renal anomalies syndrome (ORPHA:521438)
• Vertebral, cardiac, renal, and limb defects syndrome 2 - MedGen
• Vertebral, cardiac, renal, and limb defects syndrome 3 - GTR
• OMIM #617660 - VCRL1
• OMIM #617661 - VCRL2
• OMIM #618845 - VCRL3
• Congenital vertebral-cardiac-renal anomalies syndrome - GARD/NCATS
• congenital vertebral-cardiac-renal anomalies syndrome - Open Targets (MONDO_0020831)
• Congenital NAD Deficiency Disorder - GeneReviews (NBK593504)
• NAD Deficiency, Congenital Malformations, and Niacin Supplementation - NEJM 2017
• A Homozygous Deletion of Exon 5 of KYNU Resulting from Maternal Chromosome 2 Isodisomy (UPD2) Causes Catel-Manzke-Syndrome/VCRL Syndrome
• Bi-allelic Mutations in NADSYN1 Cause Multiple Organ Defects - Victor Chang Cardiac Research Institute
• Bi-allelic Mutations in NADSYN1 Cause Multiple Organ Defects - AJHG/ScienceDirect
• A metabolic signature for NADSYN1-dependent congenital NAD deficiency disorder - PMC
• NAD+ deficiency in human congenital malformations and miscarriage: A new model of pleiotropy - AJMG 2022
• Nicotinamide Adenine Dinucleotide Deficiency and Its Impact on Mammalian Development - Dunwoodie et al. 2023
• A zebrafish model of NAD+ deficiency-derived congenital disorders - bioRxiv/PubMed 39829932
• Effect of maternal dietary niacin intake on congenital anomalies: systematic review and meta-analysis
• HAAO Gene - GeneCards / OMIM 604521
• NADSYN1 gene - GeneCards / OMIM 608285
• KYNU - Alliance of Genome Resources (HGNC:6469)
• Could vitamin B-3 be the answer to miscarriages and birth defects? - Medical News Today coverage of Dunwoodie group research

Reference Validation

Checked with linkml-reference-validator 0.2.1.

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

• HP:0002510 (1 mention) - the report calls it "One reported Lennox-Gastaut-type case"; HP calls it Spastic tetraplegia
• GO:0034354 (1 mention) - the report calls it "NAD biosynthesis via nicotinamide riboside salvage pathway"; GO calls it 'de novo' NAD+ biosynthetic process from L-tryptophan
• UBERON:0002298 (1 mention) - the report calls it "vertebral column"; UBERON calls it brainstem

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

• HP:0001180 (obsolete Hand oligodactyly) (1 mention) - replaced by HP:0009380
• GO:0043420 (obsolete anthranilate metabolic process) (1 mention)

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• GO:0043420 (1 mention) - the report calls it "anthranilate metabolic process"; GO calls it obsolete anthranilate metabolic process, and lists "anthranilate catabolic process" among its other names
• GO:0033721 (1 mention) - the report calls it "3-hydroxyanthranilate 3,4-dioxygenase activity"; GO calls it aldehyde dehydrogenase (NADP+) activity
• GO:0006974 (1 mention) - the report calls it "cellular response to DNA damage stimulus, PARP-relevant"; GO calls it DNA damage response, and lists "cellular response to DNA damage stimulus" among its other names

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA, MGI.