Alternative titles; symbols
HGNC Approved Gene Symbol: ADH5
Cytogenetic location: 4q23 Genomic coordinates (GRCh38): 4:99,070,978-99,088,788 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 4q23 | AMED syndrome, digenic | 619151 | Digenic recessive | 3 |
There are at least 7 alcohol dehydrogenase (ADH) genes that catalyze the conversion of alcohols to aldehydes. Seven genes exist in a cluster on chromosome 4q (see ADH1A, 103700). ADH class III (ADH5; EC 1.1.1.1) is a zinc-containing dimeric enzyme responsible for the oxidation of long-chain alcohols and omega-hydroxy fatty acids. Unlike ADH classes I and II, ADH class III does not metabolize ethanol (Goldman et al., 1989). ADH5 is the same as formaldehyde dehydrogenase (FDH; EC 1.2.1.1), a widely occurring enzyme that catalyzes the oxidation of S-hydroxymethylglutathione, formed from formaldehyde and glutathione, into S-formylglutathione in the presence of NAD (Koivusalo et al., 1989).
Adinolfi et al. (1984) purified the chi isozyme of ADH (ADH5) from human liver and used it to raise immune sera. Its immunologic properties suggested that it has no structural similarity to either class I (see ADH1A, 103700) or class II (ADH4; 103740) isozymes. The chi isozyme was found in most human tissues, including fetal specimens of 16 weeks gestational age, and showed a preference for long chain primary alcohols with a double bond in the beta position and complex alcohols of high molecular weight, such as cinnamyl alcohol. Adinolfi et al. (1984) concluded that the locus, designated ADH5, has a separate evolutionary origin from class I and II ADH genes.
Using oligonucleotide probes based on the peptide sequence of human class III ADH, Sharma et al. (1989) screened a human placenta cDNA library and isolated an incomplete cDNA clone, which they used to obtain a full-length clone from a human testicular library. The encoded protein was identical to the enzyme purified from human liver by Adinolfi et al. (1984).
Goldman et al. (1989) isolated and sequenced a full-length cDNA for ADH5, the class III alcohol dehydrogenase. In contrast to other ADHs whose expression is more restricted, ADH5 was found to be expressed ubiquitously in human and rodent tissues. Giri et al. (1989) reported 2 possible translation initiation sites that would produce proteins of 374 and 392 amino acid residues. Class III ADH shared highest sequence identity with class II ADH.
Beisswenger et al. (1985) showed that ADH-chi is the only ADH isozyme in brain.
By examining amino acid sequences and structural and kinetic properties, Koivusalo et al. (1989) determined that ADH class III and glutathione-dependent formaldehyde dehydrogenase are identical enzymes.
Pseudogenes
Matsuo and Yokoyama (1990) demonstrated a processed pseudogene most likely derived from the ADH5 gene. Hur and Edenberg (1992) isolated several ADH5 processed pseudogenes.
Hur and Edenberg (1992) determined that the ADH5 gene contains 9 exons. Its 5-prime region contains consensus binding sites for several transcriptional regulatory proteins.
By analysis of gene products in starch gel electrophoresis, Carlock et al. (1985) assigned the class III ADH locus to chromosome 4q21-q25. Smith (1986) gave the regional assignment as 4q21-q24. By analysis of human/hamster hybrid cell lines, Goldman et al. (1989) mapped ADH5 to chromosome 4 where other ADH genes had been located. Analysis of mouse/hamster hybrid cell lines showed that the corresponding gene maps to mouse chromosome 3, which carries the other murine ADH genes.
Meera Khan et al. (1984), Van Cong et al. (1985), Hiroshige et al. (1985), and van der Goes et al. (1985) mapped the FDH gene to chromosome 4. Hiroshige et al. (1985) provided a regional assignment of 4q21-q25 by study of hybrids containing pieces of chromosome 4.
Beisswenger et al. (1985) noted that unlike previously identified ADH enzymes, ADH5 oxidizes ethanol very poorly.
Holmquist and Vallee (1991) noted that the ADH5 enzyme is essentially inactive toward formaldehyde in the absence of glutathione.
Engeland et al. (1993) reported the kinetic characterization of human class III ADH altered at position 115 to asp and to ala by in vitro mutagenesis. The results indicated that the arg115 residue is a component of the binding site for activating fatty acids and is critical for the binding of S-hydroxymethylglutathione in glutathione-dependent formaldehyde dehydrogenase activity.
Considerable evidence indicates that nitric oxide biology involves a family of NO-related molecules and that S-nitrosothiols are central to signal transduction and host defense. Liu et al. (2001) purified a single activity from E. coli, S. cerevisiae, and mouse macrophages that metabolizes S-nitrosoglutathione (GSNO), and demonstrated that it is the glutathione-dependent formaldehyde dehydrogenase. Although the enzyme is highly specific for GSNO, it controls intracellular levels of both GSNO and S-nitrosylated proteins. Such 'GSNO reductase' activity is widely distributed in mammals. Deleting the reductase gene in yeast and mice abolished the GSNO-consuming activity and increased the cellular quantity of both GSNO and protein S-nitrosothiol. Furthermore, mutant yeast cells showed increased susceptibility to a nitrosative challenge, whereas their resistance to oxidative stress was unimpaired. Liu et al. (2001) concluded that GSNO reductase is evolutionarily conserved from bacteria to humans, is critical for S-nitrosothiol homeostasis, and protects against nitrosative stress.
Benkmann et al. (1991) found no polymorphism of the FDH protein in blood samples from Koreans, Chinese, Hungarians, and Germans, when analyzed by isoelectric focusing on polyacrylamide gels followed by a specific staining for FDH activity.
In 10 patients from 8 unrelated Japanese families with AMED syndrome (AMEDS; 619151), Oka et al. (2020) identified homozygous or compound heterozygous mutations in the ADH5 gene (103710.0001-103710.0003). The mutations, which were found by whole-exome sequencing, segregated with the disorder in the families from whom parental DNA was available. Immunoblot analysis of fibroblasts from some of the patients showed a significant reduction in ADH5 protein levels compared to controls, consistent with a loss-of-function effect. Patient cells showed increased sensitivity to formaldehyde treatment compared to controls. Of note, the Fanconi anemia (see, e.g., FANCA; 227650) pathway of DNA interstrand crosslink (ICL) repair was intact. No homozygous ADH5 loss-of-function variants were identified in gnomAD or in several large Japanese control databases. However, through screening of large Japanese control databases, a homozygous S75N variant in the ADH5 gene was identified in a healthy 55-year-old woman. In vitro functional expression studies using an S75N construct showed that the mutation resulted in severely decreased protein levels and that S75N mutant cells were as sensitive to formaldehyde as ADH5-null cells, consistent with a loss-of-function effect. This suggested that ADH5 deficiency alone is not sufficient to cause AMEDS, prompting a search for another genetic contributor. Analysis of the E504K variant in the ALDH2 gene (rs671; 100650.0001) revealed that all 10 patients with AMEDS carried either 1 copy (7 cases) or 2 copies (3 cases) of the defective ALDH2 allele, confirming a digenic disorder. The healthy woman with the S75N ADH5 variant carried a homozygous wildtype ALDH2 allele. Furthermore, all 3 AMEDS cases homozygous for the E504K allele (N1254, N1037, and N1270) had more severe phenotypes with additional neurologic abnormalities (frontal lobe atrophy, leukoencephalopathy), prominent motor deterioration, AML, and early death. These findings suggested that the aldehyde detoxification activity determined by E504K influences the severity of AMEDS. In vitro functional expression studies in U2OS cells showed that while loss of either ADH5 or ALDH2 attenuated cell cycle progression, loss of both genes led to significant inhibition of DNA replication after formaldehyde treatment. ADH5-null cells were not adversely affected by treatment with certain aldehydes. Patient-derived AMEDS cells showed significant DNA damage after formaldehyde exposure, which could be completely rescued by ectopic expression of either wildtype ADH5 or ALDH2, suggesting that both genes are involved in formaldehyde detoxification. CD34+ hematopoietic progenitor stem cells with loss of ADH5 combined with the ALDH2 variant had impaired proliferation and differentiation capacity, suggesting that formaldehyde detoxification deficiency can cause a wide range of hematopoietic abnormalities. Loss of Adh5 function in combination with reduced Aldh2 activity recapitulated the phenotype of AMEDS in mice (see ANIMAL MODEL). Oka et al. (2020) emphasized that AMEDS is a true digenic disorder, since variations in 2 distinct genes (ADH5 and ALDH2) are necessary and sufficient to cause the disease. Although the ALDH2 variant influences the severity of the disease, it is still essential for disease development. The findings suggested a mechanism in which defects in the enzymatic detoxification processes of highly reactive genotoxic chemicals, such as formaldehyde, results in the accumulation of DNA damage that overburdens DNA repair pathways, thus causing multisystemic effects.
Liu et al. (2004) generated mice with a targeted deletion of the Gsnor gene. Gsnor -/- mice exhibited substantial increases in whole-cell S-nitrosylation, tissue damage, and mortality following endotoxic or bacterial challenge. Furthermore, Gsnor -/- mice had increased basal levels of S-nitrosothiols (SNOs) in red blood cells and were hypotensive under anesthesia. Thus, Liu et al. (2004) proposed that SNOs regulate innate immune and vascular function and are cleared actively to ameliorate nitrosative stress. They concluded that nitrosylation of cysteine thiols is a critical mechanism of nitric oxide function in both health and disease.
S-nitrosoglutathione (GSNO), an endogenous bronchodilator, is depleted from asthmatic (see 600807) airways, suggesting a protective role. Que et al. (2005) reported that, following allergen challenge, wildtype mice exhibiting airway hyperresponsivity had increased airway levels of Gsnor and were depleted of lung S-nitrosothiols (SNOs). In contrast, mice with genetic deletion of Gsnor exhibited increases in lung SNOs and were protected from airway hyperresponsivity. Que et al. (2005) concluded that endogenous SNOs, governed by GSNOR, are critical regulators of airway responsivity.
Oka et al. (2020) generated digenic mice lacking Adh5 and carrying a heterozygous or homozygous Aldh2 E506K allele (equivalent to human E504K). Digenic mutant mice showed severe postnatal growth failure with cachexia, skin hyperpigmentation, and anemia associated with decreased numbers of self-renewing hematopoietic stem cells compared to controls. There was a dose-dependent effect showing that heterozygosity or homozygosity for the Aldh2 variant underlies the severity of the clinical manifestations.
In 5 children from 3 unrelated Japanese families (families 1, 4, and 6), with AMED syndrome (AMEDS; 619151), Oka et al. (2020) identified a homozygous 1-bp deletion (c.966delG) in exon 8 of the ADH5 gene, resulting in a frameshift and premature termination (trp322 to ter, W322X). Four additional patients (from families 3, 5, 7, and 8) with the disorder were compound heterozygous for W322X and a c.832G-C transversion in exon 7 of the ADH5 gene, resulting in an ala278-to-pro (A278P; 103710.0003) substitution. All patients also carried a homozygous or heterozygous E504K variant in the ALDH2 gene (100650.0001), resulting in deficiency of that enzyme and confirming a digenic disorder. The mutations, which were found by whole-exome sequencing (ADH5) or direct sequencing (ALDH2), segregated with the disorders in the families in whom parental DNA was available. No homozygous ADH5 loss-of-function variants were identified in gnomAD or in several large Japanese control databases. Immunoblot analysis of fibroblasts from some of the patients showed a significant reduction in ADH5 protein levels compared to controls, consistent with a loss-of-function effect. Patient cells showed increased sensitivity to formaldehyde treatment and inhibition of DNA replication compared to controls.
In a Japanese girl (patient N0611) with AMED syndrome (AMEDS; 619151), Oka et al. (2020) identified compound heterozygous mutations in the ADH5 gene: a G-to-A transition in intron 5 (c.564+1G-A) of the ADH5 gene, resulting in a splice site defect, and A278P (103710.0003). She also carried a heterozygous E504K variant in the ALDH2 gene (100650.0001), resulting in deficiency of that enzyme and confirming a digenic disorder. The mutations, which were found by whole-exome sequencing (ADH5) or direct sequencing (ALDH2), segregated with the disorder in the family. Immunoblot analysis of patient fibroblasts showed a significant reduction in ADH5 protein levels compared to controls, consistent with a loss-of-function effect. Patient cells showed increased sensitivity to formaldehyde treatment and inhibition of DNA replication compared to controls.
For discussion of the c.832G-C transversion in exon 7 of the ADH5 gene, resulting in an ala278-to-pro (A278P) substitution, that was found in compound heterozygous state in 5 unrelated Japanese patients with AMED syndrome (AMEDS; 619151) by Oka et al. (2020), see 103710.0001 and 103710.0002.
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