Alternative titles; symbols
HGNC Approved Gene Symbol: HAAO
Cytogenetic location: 2p21 Genomic coordinates (GRCh38) : 2:42,767,089-42,792,583 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 2p21 | Vertebral, cardiac, renal, and limb defects syndrome 1 | 617660 | Autosomal recessive | 3 |
3-Hydroxyanthranilate 3,4-dioxygenase (HAAO; EC 1.13.11.6) is a monomeric cytosolic protein belonging to the family of intramolecular dioxygenases containing nonheme ferrous iron. It is widely distributed in peripheral organs, such as liver and kidney, and is also present in low amounts in the central nervous system (Foster et al., 1986). Within rat brain, Haao appears to be mainly located in glial cells (Kohler et al., 1988). HAAO catalyzes the synthesis of quinolinic acid (QUIN) from 3-hydroxyanthranilic acid (3HAA). QUIN is an excitotoxin whose toxicity is mediated by its ability to activate glutamate N-methyl-D-aspartate receptors (see 602717). Increased cerebral levels of QUIN may participate in the pathogenesis of neurologic and inflammatory disorders. HAAO has been suggested to play a role in disorders associated with altered tissue levels of QUIN (summary by Malherbe et al., 1994).
HAAO is also involved in the de novo NAD(H) synthesis pathway, using niacin from dietary input (summary by Shi et al., 2017).
By screening a human hepatoma cell line (HepG2) cDNA library with a rat Haao cDNA, Malherbe et al. (1994) isolated a full-length human HAAO cDNA. The deduced 286-amino acid HAAO protein has a calculated molecular mass of approximately 32.6 kD. Immunoblot analysis of recombinant HAAO expressed in human embryonic kidney fibroblast cells detected a polypeptide with an apparent molecular mass of 32 kD. Northern blot analysis of human liver and HepG2 cells showed that HAAO is expressed as an approximately 1.3-kb transcript.
Gross (2014) mapped the HAAO gene to chromosome 2p21 based on an alignment of the HAAO sequence (GenBank BC029510) with the genomic sequence (GRCh37).
In 2 unrelated patients, each born of consanguineous parents, with vertebral, cardiac, renal, and limb defects syndrome-1 (VCRL1; 617660), Shi et al. (2017) identified homozygous truncating mutations in the HAAO gene (604521.0001 and 604521.0002). The mutations, which were found by whole-exome or whole-genome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the families. In vitro functional expression studies showed that both mutations essentially abolished HAAO enzymatic activity. Analysis of patient plasma showed increased levels of the upstream metabolite 3HAA and decreased levels of the downstream metabolites NAD and NAH(H). Both patients belonged to a pair of dizygotic twins; their twins were unaffected and heterozygous for the mutation. Studies in mice, which have different niacin levels compared to humans, indicated that the congenital malformations found in humans resulted from deficient NAD levels rather than increased 3HAA. Shi et al. (2017) noted that NAD is a cofactor with broad cellular effects, including ATP production, macromolecular biosynthesis, redox reactions, energy metabolism, DNA repair, and modulation of transcription factors, all of which play an important role in embryogenesis.
In 3 unrelated patients with VCRL1, Szot et al. (2021) identified compound heterozygous or homozygous mutations in the HAAO gene (604521.0003-604521.0007). Yeast with a homozygous knockout for bna1, the ortholog of human HAAO, were transformed with plasmids containing HAAO with each mutation or with wildtype HAAO. Each mutant HAAO resulted in smaller yeast mass compared to wildtype when grown in niacin-free culture media. NAD levels were also reduced in yeast transformed with the mutant HAAO plasmids compared to wildtype. Szot et al. (2021) concluded that the compromised growth of the bna1 knockout yeast transfected with each mutant HAAO was a result of abnormal HAAO enzyme activity.
Shi et al. (2017) found that Haao-null mice were viable and normal. Plasma analysis showed increased 3HAA levels, but normal NAD levels. The authors noted that mice have increased niacin levels compared to humans and that mouse embryos may receive niacin from their mothers, resulting in a buffering effect on genetic-based NAD deficiency. These findings suggested that the congenital malformations found in humans with increased levels of 3HAA but decreased levels of NAD, resulted from the deficient NAD levels. Indeed, further studies in mutant mice born to mothers on a niacin-free diet showed that NAD deficiency due to lack of Haao resulted in multiple defects, including defects in vertebral segmentation, heart defects, small kidney, cleft palate, talipes, syndactyly, and caudal agenesis. Supplementation of Haao-null mouse embryos with niacin during gestation restored NAD levels and prevented the disruption of embryogenesis.
In a boy, born of consanguineous Iraqi parents (family A), with vertebral, cardiac, renal, and limb defects syndrome-1 (VCRL1; 617660), Shi et al. (2017) identified a homozygous 1-bp duplication (c.483dupT) in exon 6 of the HAAO gene, resulting in a frameshift and premature termination (Asp162Ter). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. The variant was filtered against the ExAC database and was classified as pathogenic based on the American College of Medical Genetics guidelines. In vitro functional expression studies showed that the mutation essentially abolished HAAO enzymatic activity.
In a girl, born of consanguineous Lebanese parents (family B), with vertebral, cardiac, renal, and limb defects syndrome-1 (VCRL1; 617660), Shi et al. (2017) identified a homozygous c.558G-A transition in exon 7 of the HAAO gene, resulting in a trp186-to-ter (W186X) substitution. The mutation, which was found by whole-genome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. The variant was not found in the ExAC database and was classified as pathogenic based on the American College of Medical Genetics guidelines. In vitro functional expression studies showed that the mutation essentially abolished HAAO enzymatic activity.
In a patient (family 1), born of unrelated parents of Hispanic origin, with vertebral, cardiac, renal, and limb defects syndrome-1 (VCRL1; 617660), Szot et al. (2021) identified compound heterozygous mutations in the HAAO gene: a c.128G-A transition (c.128G-A, NM_012205.3), resulting in an arg43-to-lys (R43K) substitution, and a c.141C-A transversion, resulting in a his47-to-gln (H47Q; 604521.0004) substitution. The mutations were identified by whole-exome sequencing and the parents were shown to be mutation carriers. Neither mutation was present in the gnomAD database. Yeast with a homozygous knockout for bna1 were transformed with plasmids containing HAAO with each of the mutations or with wildtype HAAO. Each mutant HAAO resulted in smaller yeast mass compared to wildtype when grown in niacin-free culture media. NAD levels were also reduced in yeast transformed with the mutant HAAO plasmids compared to wildtype.
For discussion of the c.141C-A transversion (c.141C-A, NM_012205.3) in the HAAO gene, resulting in a his47-to-gln (H47Q) substitution, that was found in compound heterozygous state in a patient with vertebral, cardiac, renal, and limb defects syndrome-1 (VCRL1; 617660) by Szot et al. (2021), see 604521.0003.
In a patient (family 2), born of unrelated parents with vertebral, cardiac, renal, and limb defects syndrome-1 (VCRL1; 617660), Szot et al. (2021) identified a homozygous 1-bp deletion (c.43del, NM_012205.3) in the HAAO gene, resulting in a frameshift and premature termination (Arg15GlyfsTer99). The mutation was identified by whole-exome sequencing and the parents were shown to be mutation carriers. The mutation had an allele frequency of 0.00000443 in the gnomAD database. Yeast with a homozygous knockout for bna1 were transformed with a plasmid containing HAAO with the c.43del mutation or with wildtype HAAO. The mutant HAAO resulted in smaller yeast mass compared to wildtype when grown in niacin-free culture media. NAD levels were also reduced in the yeast transformed with the mutant HAAO plasmid compared to wildtype.
In a fetus (family 3) with vertebral, cardiac, renal, and limb defects syndrome-1 (VCRL1; 617660), Szot et al. (2021) identified compound heterozygous mutations in the HAAO gene: a c.323G-A transition (c.323G-A, NM_012205.3), resulting in an arg108-to-gln (R108Q) substitution, and a c.301G-T transversion, resulting in a gly101-to-trp (G101W; 604521.0007) substitution. The mutations were identified by trio whole-exome sequencing and the parents were shown to be mutation carriers. Neither mutation was present in the gnomAD database. Yeast with a homozygous knockout for bna1 were transformed with plasmids containing HAAO with either mutation or with wildtype HAAO. Each mutant HAAO resulted in smaller yeast mass compared to wildtype when grown in niacin-free culture media. NAD levels were also reduced in yeast transformed with the mutant HAAO plasmids compared to wildtype. A similarly affected sib fetus was not tested for the mutations.
For discussion of the c.301G-T transversion (c.301G-T, NM_012205.3) in the HAAO gene, resulting in a gly101-to-trp (G101W) substitution, that was found in compound heterozygous state in a fetus with vertebral, cardiac, renal, and limb defects syndrome-1 (VCRL1; 617660) by Szot et al. (2021), see 604521.0006.
Foster, A. C., White, R. J., Schwarcz, R. Synthesis of quinolinic acid by 3-hydroxyanthranilic acid oxygenase in rat brain tissue in vitro. J. Neurochem. 47: 23-30, 1986. [PubMed: 2940338] [Full Text: https://doi.org/10.1111/j.1471-4159.1986.tb02826.x]
Gross, M. B. Personal Communication. Baltimore, Md. 3/24/2014.
Kohler, C., Eriksson, L. G., Okuno, E., Schwarcz, R. Localization of quinolinic acid metabolizing enzymes in the rat brain. Immunohistochemical studies using antibodies to 3-hydroxyanthranilic acid oxygenase and quinolinic acid phosphoribosyltransferase. Neuroscience 27: 49-76, 1988. [PubMed: 2974127] [Full Text: https://doi.org/10.1016/0306-4522(88)90219-9]
Malherbe, P., Kohler, C., Da Prada, M., Lang, G., Kiefer, V., Schwarcz, R., Lahm, H.-W., Cesura, A. M. Molecular cloning and functional expression of human 3-hydroxyanthranilic-acid dioxygenase. J. Biol. Chem. 269: 13792-13797, 1994. [PubMed: 7514594]
Shi, H., Enriquez, A., Rapadas, M., Martin, E. M. M. A., Wang, R., Moreau, J., Lim, C. K., Szot, J. O., Ip, E., Hughes, J. N., Sugimoto, K., Humphreys, D. T., and 21 others. NAD deficiency, congenital malformations, and niacin supplementation. New Eng. J. Med. 377: 544-552, 2017. [PubMed: 28792876] [Full Text: https://doi.org/10.1056/NEJMoa1616361]
Szot, J. O., Slavotinek, A., Chong, K., Brandau, O., Nezarati, M., Cueto-Gonzalez, A. M., Patel, M. S., Devine, W. P., Rego, S., Acyinena, A. P., Shannon, P., Myles-Reid, D., and 17 others. New cases that expand the genotypic and phenotypic spectrum of congenital NAD deficiency disorder. Hum. Mutat. 42: 862-876, 2021. [PubMed: 33942433] [Full Text: https://doi.org/10.1002/humu.24211]