Clinical characteristics.

Congenital NAD deficiency disorder (CNDD) is a multisystem condition in which cardiac, renal, vertebral, and limb anomalies are common, mimicking the clinical features described in VACTERL association. Congenital heart defects can include left-sided heart lesions, right-sided heart lesions, or both. Almost all surviving individuals have short stature, many with disproportionately shortened limbs. Vertebral anomalies, including hemivertebrae and vertebral fusion, occur frequently, often with rib anomalies. Renal anomalies may be severe, including dysplasia/hypoplasia and renal agenesis. Developmental delay / intellectual disability has been reported in more than half of affected individuals, although some affected individuals have had normal development, and some individuals succumbed to their congenital anomalies before developmental assessment could be performed. Other less common features may include cleft palate, eye anomalies, sensorineural hearing loss, tracheoesophageal fistula, polysplenia, anteriorly displaced anus, tethered spinal cord, cystic hygroma, epilepsy, hypothyroidism, and hypoparathyroidism.

Diagnosis/testing.

The diagnosis of CNDD is established in a proband with suggestive findings and biallelic pathogenic variants in HAAO, KYNU, or NADSYN1 identified by molecular genetic testing.

Management.

Treatment of manifestations: There is no cure for CNDD. Supportive care includes standard treatment for congenital anomalies (congenital heart defects, cleft palate, limb anomalies, scoliosis, tethered spinal cord, renal anomalies, tracheoesophageal fistula / pyloric stenosis / laryngeal web, polysplenia, and strabismus/ptosis) and for functional/medical issues (hearing loss, developmental delay / intellectual disability, epilepsy, hypothyroidism, and hyperparathyroidism).

Surveillance: At each visit: measurement of growth parameters; evaluation of nutrition status and safety of oral intake; assessment of mobility and self-help skills; monitoring of developmental progress and educational needs; monitoring of seizures; and assessment for new manifestations, such as changes in tone. At each visit until skeletal maturity: monitoring for scoliosis. Annually or as clinically indicated: audiology evaluation; ophthalmology evaluation; assessment of thyroid function; and serum calcium levels in those with hypoparathyroidism. For those with renal anomalies: measurement of blood pressure at each visit and renal function tests annually or as clinically indicated.

Agents/circumstances to avoid: Avoidance of medications that impair kidney function, in those with renal aplasia (solitary kidney) and/or known impaired kidney function.

Genetic counseling.

CNDD is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for a CNDD-related pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once the CNDD-related pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal and preimplantation genetic testing are possible.

Suggestive Findings

CNDD should be suspected in individuals with the following imaging findings, further clinical features, and family history.

Imaging findings

• Congenital heart defects affecting:
  • Both the left- and right-sided structures (tetralogy of Fallot) OR
  • The left-sided structures (hypoplastic left heart, mitral valve defects, coarctation of the aorta, bicuspid aortic valve) OR
  • The right-sided structures (absent pulmonary trunk, double-outlet right ventricle)
• Renal anomalies, including renal aplasia, hypoplasia, and dysplasia
• Vertebral anomalies, including butterfly vertebra, hemivertebra, wedge-shaped vertebra, and fused vertebra, on spinal radiographs
• Shortened long bones, including rhizomelia and brachymelia, usually affecting both the arms and legs
• Short metacarpals with accessory ossicles on hand radiographs

Further clinical features

• Short stature, frequently but not always with shortened long bones
• Microcephaly
• Nonspecific dysmorphic features, including cupped and/or low-set ears (See Clinical Description.)
• Sensorineural hearing loss
• Nuchal redundancy or cystic hygroma
• Cutaneous syndactyly of fingers and/or toes
• Other hand anomalies, including hyperphalangism, short phalanges, and/or short metacarpals
• Developmental delay / intellectual disability, ranging from mild to severe, although some affected individuals have no developmental issues
• Sacral dimple or other sacral stigmata, such as a sacral hair tuft
• Clubfeet

Family history is consistent with autosomal recessive inheritance (e.g., affected sibs and/or parental consanguinity). Absence of a known family history does not preclude the diagnosis.

Establishing the Diagnosis

The diagnosis of CNDD is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in HAAO, KYNU, or NADSYN1 identified by molecular genetic testing (see Table 1).

Note: (1) Per ACMG/AMP variant interpretation guidelines, the terms "pathogenic variant" and "likely pathogenic variant" are synonymous in a clinical setting, meaning that both are considered diagnostic and can be used for clinical decision making [Richards et al 2015]. Reference to "pathogenic variants" in this section is understood to include "likely pathogenic" variants. (2) Identification of biallelic HAAO, KYNU, or NADSYN1 variants of uncertain significance (or of one known pathogenic variant in a given gene and one variant of uncertain significance in that same gene) does not establish or rule out the diagnosis.

Molecular genetic testing approaches can include a combination of gene-targeted testing (multigene panel) and comprehensive genomic testing (exome sequencing, genome sequencing) depending on the phenotype.

Gene-targeted testing requires that the clinician determine which gene(s) are likely involved, whereas genomic testing does not. Individuals with the distinctive findings described in Suggestive Findings may be diagnosed using gene-targeted testing (see Option 1), whereas those with a phenotype indistinguishable from many other inherited disorders with multiple congenital anomalies are more likely to be diagnosed using genomic testing (see Option 2).

Clinical Description

Congenital NAD deficiency disorder (CNDD) is a multisystem condition in which cardiac, renal, vertebral, and limb anomalies are common. Short stature with shortened long bones, developmental delay / intellectual disability, and other organ system involvement may also be present [Mark 2022]. The morbidity and mortality of these anomalies can be quite variable. To date, 27 individuals have been identified with biallelic pathogenic variants in HAAO, KYNU, or NADSYN1, of which 16 are still living [Shi et al 2017; Ehmke et al 2020; Szot et al 2020; Schüle et al 2021; Szot et al 2021; Kortbawi et al 2022; Aubert-Mucca et al 2023; Erbs et al 2023; Authors, personal observation]. The following description of the phenotypic features associated with this condition is based on these reports.

Cardiovascular anomalies. Structural heart defects have been reported in all affected individuals thus far. Hypoplastic left heart (8 individuals) and tetralogy of Fallot (3 individuals) were the most common. However, coarctation of the aorta, aortic stenosis, bicuspid aortic valve, mitral valve defects, absent pulmonary trunk, double-outlet right ventricle, Shone complex (a combination of membranous or muscular subvalvular aortic stenosis, supravalvular mitral membrane, and parachute mitral valve), ventricular septal defect, atrial septal defect, anomalous left coronary artery from the pulmonary artery, and patent ductus arteriosus have also been reported. Two-vessel umbilical cord has also been described.

Growth issues

• Almost all surviving individuals have short stature, many with disproportionately shortened limbs, which is likely due to NAD deficiency. Height z scores range from +0.25 to −6.1.
• A minority of individuals have microcephaly, with z scores ranging from −2.3 to −6.4.

Musculoskeletal/neuromuscular findings. Vertebral anomalies, including hemivertebrae and vertebral fusion, occur frequently, often with rib anomalies. Disproportionately shortened long bones are common. Joint hypermobility, including hypermobile fingers, has also been described.

• Upper limb anomalies may include single palmar crease, hyperphalangism, short phalanges, and short metacarpals with accessory ossicles. A transverse terminal hand reduction with rudimentary fifth digit has also been observed.
• Lower limb anomalies may include shortened metatarsals, limb asymmetry, and absent toes.
• Syndactyly has been reported in both fingers and toes.
• Neuromuscular limb anomalies may include talipes, arthrogryposis, and pterygia.

Developmental delay / intellectual disability. Some affected individuals died from complications of their congenital anomalies before developmental assessment could be performed. Of those who were assessed, there was a range from normal to severe developmental delay / intellectual disability. One individual had isolated speech delay, and one had global developmental delay and autism spectrum disorder. The etiology of these delays is still uncertain. Four affected individuals have been reported with normal development.

Renal anomalies. Renal findings are common and frequently severe. Renal dysplasia/hypoplasia (8 individuals) is the most reported defect, along with unilateral renal agenesis (6 individuals). Bilateral renal agenesis, ureter agenesis, and hydronephrosis have occurred with less frequency.

Craniofacial features. A minority of affected individuals have a range of nonspecific dysmorphic features. Such features may include brachycephaly, low or high anterior hairline, narrow forehead, prominent supraorbital ridges, highly arched eyebrows, widely spaced eyes, narrow spaced eyes, upslanted and downslanted palpebral fissures, short palpebral fissures, epicanthal folds, depressed nasal bridge, broad nose, and thick nasal alae. Microretrognathia and cleft of the soft palate have also been reported. There does not appear to be a recognizable facial gestalt.

Neurologic

• One individual with seizures (Lenox-Gastaut syndrome) has been reported.
• Small brain on autopsy was recorded in two individuals. Five other individuals had documented microcephaly (see Growth issues above).
• Other findings on brain imaging include hydrocephalus and hypoplastic cerebellum.

Ears/hearing. Sensorineural hearing loss has been reported in four individuals, two of whom had documented inner ear abnormalities. Cupped ears and low-set ears are common, and posteriorly rotated ears have been reported.

Gastrointestinal findings. Tracheoesophageal fistula, polysplenia, hepatomegaly (from congestion), anteriorly displaced anus, and likely pyloric stenosis have all been identified.

Other findings

• Eyes. Strabismus and ptosis were noted in one affected individual, while ocular crystals and hypopigmented iris with nodules were reported in another affected individual.
• Respiratory findings include hypoplastic right lung and laryngeal web.
• Endocrine findings include hypothyroidism identified at birth in two affected individuals and hypoparathyroidism identified at birth in one affected individual.
• Lymphatic findings include cystic hygroma and nuchal redundancy or thickening.

Prognosis. The life span for individuals with this condition is not known, although it is likely dependent on the severity and type of congenital anomalies in any given affected individual. Of the nine known individuals who did not survive, five were either terminated or did not survive pregnancy due to their anomalies, while four did not survive the first year of life due to severe birth defects. The current oldest known living person is age 30 years [Erbs et al 2023].

Phenotype Correlations by Gene

The phenotype does not differ by the associated gene.

Genotype-Phenotype Correlations

No genotype-phenotype correlations for HAAO, KYNU, or NADSYN1 have been identified.

Prevalence

To date, there are 27 reported individuals from 25 families with CNDD, of whom 16 are still living.

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs in an individual diagnosed with CNDD, the evaluations summarized in Table 4 (if not performed as part of the evaluation that led to the diagnosis) are recommended.

Treatment of Manifestations

There is no cure for congenital NAD deficiency disorder.

Supportive care to improve quality of life, maximize function, and reduce complications is recommended. This ideally involves multidisciplinary care by specialists in relevant fields (see Table 5).

Surveillance

To monitor existing manifestations, the individual's response to supportive care, and the emergence of new manifestations, the evaluations summarized in Table 6 are recommended.

Agents/Circumstances to Avoid

Avoidance of medications that impair kidney function, in those with renal aplasia (solitary kidney) and/or known impaired kidney function.

Evaluation of Relatives at Risk

It is appropriate to clarify the genetic status of apparently asymptomatic older and younger at-risk relatives of an affected individual in order to identify as early as possible those who would benefit from more in-depth evaluation for occult congenital malformations.

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Mode of Inheritance

Congenital NAD deficiency disorder (CNDD) is inherited in an autosomal recessive manner.

Risk to Family Members

Parents of a proband

• The parents of an affected child are presumed to be heterozygous for a HAAO, KYNU, or NADSYN1 pathogenic variant.
• Molecular genetic testing is recommended for the parents of the proband to confirm that both parents are heterozygous for a causative pathogenic variant and to allow reliable recurrence risk assessment.
• If a pathogenic variant is detected in only one parent and parental identity testing has confirmed biological maternity and paternity, it is possible that one of the pathogenic variants identified in the proband occurred as a de novo event in the proband or as a postzygotic de novo event in a mosaic parent [Jónsson et al 2017]. If the proband appears to have homozygous pathogenic variants (i.e., the same two pathogenic variants), additional possibilities to consider include:
  • A single- or multiexon deletion in the proband that was not detected by sequence analysis and that resulted in the artifactual appearance of homozygosity;
  • Uniparental isodisomy for the parental chromosome with the pathogenic variant that resulted in homozygosity for the pathogenic variant in the proband. Maternal isodisomy of chromosome 2 has been reported in a proband with KYNU-related CNDD [Schüle et al 2021].
• Heterozygotes (carriers) are asymptomatic and are not at risk of developing the disorder.

Sibs of a proband

• If both parents are known to be heterozygous for a CNDD-related pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
• Heterozygotes (carriers) are asymptomatic and are not at risk of developing the disorder.

Offspring of a proband. Unless an affected individual's reproductive partner also has CNDD or is a carrier, offspring will be obligate heterozygotes (carriers) for a CNDD-related pathogenic variant.

Other family members. Each sib of the proband's parents is at a 50% risk of being a carrier of a CNDD-related pathogenic variant.

Carrier Detection

Carrier testing for at-risk relatives requires prior identification of the CNDD-related pathogenic variants in the family.

Related Genetic Counseling Issues

See Management, Evaluation of Relatives at Risk for information on evaluating at-risk relatives for the purpose of early diagnosis and treatment.

Family planning

• The optimal time for determination of genetic risk and discussion of the availability of prenatal/preimplantation genetic testing is before pregnancy.
• It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to young adults who are affected, are carriers, or are at risk of being carriers.
• It is appropriate to offer carrier testing for reproductive partners of known carriers, particularly if consanguinity is likely.

Prenatal Testing and Preimplantation Genetic Testing

Once the CNDD-related pathogenic variants have been identified in an affected family member, prenatal and preimplantation genetic testing are possible.

Differences in perspective may exist among medical professionals and within families regarding the use of prenatal testing. While most centers would consider use of prenatal testing to be a personal decision, discussion of these issues may be helpful.

Molecular Pathogenesis

Nicotinamide adenine dinucleotide in the oxidized form (known as NAD⁺) plays critical cellular functions, including as an electron acceptor required for ATP synthesis. NAD⁺ can be synthesized de novo biologically via one of the following three mechanisms: from tryptophan through the NAD⁺ de novo synthesis pathway; from the deaminated precursor nicotinic acid (NA) through the Preiss-Handler pathway; and from NA derivatives (NAD⁺ precursors nicotinamide mononucleotide [NMN] and nicotinamide riboside [NR]) using a salvage pathway [Zapata-Pérez et al 2021]. Individuals with biallelic pathogenic variants in the NAD⁺ de novo synthesis pathway demonstrate decreased production of NAD, either through measurement of human NAD levels, or in mouse and yeast models of specific pathogenic variants that have been identified in individuals with Congenital NAD deficiency disorder [Shi et al 2017, Szot et al 2020, Szot et al 2021].

Mechanism of disease causation. Loss of function

Acknowledgments

The authors would like to thank all individuals with Congenital NAD deficiency disorder and their families for sharing their medical and personal stories.

We acknowledge funds awarded to SLD to conduct this research by the National Health and Medical Research Council (NHMRC) Principal Research Fellowship (ID1135886), Leadership Level 3 Fellowship (ID2007896), and Project Grant (ID1162878); a NSW Health Cardiovascular Research Capacity Program Senior Researcher Grant; and philanthropic support from the Key Foundation.

Revision History

• 27 July 2023 (ma) Review posted live
• 15 December 2022 (pm) Original submission

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