Alternative titles; symbols
HGNC Approved Gene Symbol: MNX1
SNOMEDCT: 413936007;
Cytogenetic location: 7q36.3 Genomic coordinates (GRCh38) : 7:157,004,854-157,010,663 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 7q36.3 | Currarino syndrome | 176450 | Autosomal dominant | 3 |
Deguchi and Kehrl (1991) found that 2 human homeobox genes, HB9 (MNX1) and HB24 (HLX1; 142995), are highly expressed in CD34-positive (142230) marrow cells but not in CD34-depleted marrow cells. Their expression was readily downregulated during the differentiation of hematopoietic progenitors to specific cell lineages.
Harrison et al. (1994) isolated a human HB9 cDNA encoding a deduced 403-amino acid protein with a predicted molecular mass of 41 kD. The HB9 homeodomain was found to be most similar to that of the Drosophila homeobox box gene proboscipedia. Northern blot analysis detected a major 2.2-kb transcript in hematopoietic cell lines. The transcript was most prevalent in several human B cell lines and K562 cells.
Harrison et al. (1994) determined that the HB9 gene contains 3 exons spread over 6 kb.
Ross et al. (1998) noted that an STS (sequence tagged site) from the 3-prime untranslated region (UTR) of the HLXB9 gene was on the chromosome 7 map; after typing various YACs from the 7q36 region, Ross et al. (1998) determined that the HLXB9 gene is located in the D7S559-D7S2423 interval.
Based on the expression pattern of HLXB9, Harrison et al. (1994) suggested its involvement in regulating gene transcription in lymphoid and pancreatic tissues.
Ross et al. (1998) were prompted to investigate the sacral expression of HLXB9 by a report of tailbud expression of the homolog in Xenopus laevis. Ross et al. (1998) found that HLXB9 was detectable in the sacral region during embryogenesis, albeit predominantly in the anterior horn regions of the spinal cord.
In 2 dominantly inherited sacral agenesis families (see Currarino syndrome, 176450), Lynch et al. (1995) found linkage to 7q36 markers. Ross et al. (1998) refined the subchromosomal localization in several additional hereditary sacral agenesis families and identified causative mutations in the HLXB9 gene (142994.0001-142994.0006).
To define more precisely the involvement of HLXB9 in different phenotypic subgroups of anorectal malformations (ARMs), Belloni et al. (2000) did a mutation screen in 27 individuals showing different sacral conditions. Of the subgroups studied, mutation in HLXB9 was found only in the Currarino syndrome. In 7 of 10 patients with Currarino syndrome, abnormality of the HLXB9 was found. Four patients harbored, within the coding sequence, heterozygous point mutations that would be predicted to cause deleterious changes in the protein; one of these patients had a donor splice site mutation. The entire HLXB9 gene in 2 patients and possibly a third was found to be deleted. The authors found no evidence of HLXB9 involvement in caudal regression (categories III and V) or in total sacral agenesis (categories I and II).
Hagan et al. (2000) reported an extensive mutation survey that identified mutations in the HLXB9 gene in 20 of 21 patients with familial Currarino syndrome. Mutations were also detected in 2 of 7 sporadic patients; the authors suggested that the remainder could be explained by undetected mosaicism for an HLXB9 mutation or by genetic heterogeneity in the sporadic patients. Of the mutations identified in the 22 index patients, 19 were intragenic and included 11 mutations that could lead to the introduction of a premature termination codon. The other 8 mutations were missense mutations that were significantly clustered in the homeodomain, resulting, in each patient, in nonconservative substitution of a highly conserved amino acid. All of the intragenic mutations were associated with comparable phenotypes. The only genotype-phenotype correlation appeared to be the occurrence of developmental delay in the case of 3 patients with microdeletions. HLXB9 expression was analyzed during early human development in a period spanning Carnegie stages 12 to 21. A signal was detected in the basal plate of the spinal cord and hindbrain and in the pharynx, esophagus, stomach, and pancreas. Significant spatial and temporal expression differences were evident when expression of the gene in human and mouse were compared. This may partly explain the significant human-mouse differences in the mutant phenotype.
Kochling et al. (2001) identified a total of 5 HLXB9 mutations (4 of which were novel) in 4 of 4 families and 1 of 5 sporadic cases with Currarino syndrome. A detailed clinical investigation failed to identify any obvious genotype-phenotype correlation. In all familial cases an autosomal dominant transmission was observed. Although 10 of 23 patients with HLXB9 mutations were asymptomatic, radiologic investigation revealed characteristic phenotypic features in all patients. The complete triad, consisting of a presacral mass, anorectal malformation, and sacral agenesis, was found in only 8 of the 23 patients. A highly variable phenotype was seen within 3 of the families, whereas affected members of 1 family showed almost identical phenotypes. The distribution of these and previously described HLXB9 mutations indicated mutational predilection sites within exon 1 and within the homeodomain (including all missense mutations). All reported mutations directly or indirectly affected the DNA-binding homeodomain, as all in-frame mutations were located within the homeodomain and mutations N-terminal of the homeodomain were frameshift mutations leading to HB9 haploinsufficiency. Since mutations have been detected in most patients with familial Currarino syndrome, Kochling et al. (2001) found somatic mosaicism to be the best explanation for the low mutation detection in sporadic cases.
In affected members of a 3-generation family segregating Currarino syndrome, Urioste et al. (2004) identified a frameshift mutation in the HLXB9 gene (142994.0009). Malignant transformation of a presacral teratoma was observed in the 22-year-old proband, and presacral teratomas were found in 6 other family members, including the 3 asymptomatic individuals. Of 9 affected members, only 2 displayed the complete triad.
In affected members of a 4-generation family with Currarino syndrome, Wang et al. (2006) identified heterozygosity for a nonsense mutation in the HLXB9 gene (142994.0010).
In most mammals, the pancreas develops from the foregut endoderm as ventral and dorsal buds. These buds fuse and develop into a complex organ composed of endocrine, exocrine, and ductal components. This developmental process depends upon an integrated network of transcription factors. Gene targeting experiments in mice revealed critical roles for PDX1 (600733), ISL1 (600366), PAX4 (167413), PAX6 (607108), and NKX2.2. The HLXB9 gene is prominently expressed in adult human pancreas. To facilitate study of the role of HLXB9 in the development and function of the pancreas, Harrison et al. (1999) isolated the mouse HLXB9 ortholog, Hlxb9. They found that during mouse development, the dorsal and ventral pancreatic ducts and mature beta cells in the islets of Langerhans express Hlxb9. In gene targeting experiments, mice homozygous for a null mutation of the Hlxb9 gene failed to show development of the dorsal lobe of the pancreas. The remnant Hlxb9 -/- pancreas had small islets of Langerhans with reduced numbers of insulin-producing beta cells. Hlxb9 -/- beta cells expressed low levels of the glucose transporter Glut2 (138160) and homeodomain factor Nkx6.1 (602563). Thus, Harrison et al. (1999) concluded that HLXB9 is key to normal pancreas development and function.
Catala (2002) reviewed caudal development, the evidence coming from analyses of mutant mice, indicating the involvement of T-box transcription factors and components of the Wnt signaling pathway in cellular migration and mesoderm formation in the caudal embryo. The basis of sacral agenesis in the human in mutations of the HLXB9 transcription factor provides further insight on the developmental program of the caudal embryo.
Najfeld et al. (1992) used HB9 and HB24 cDNA probes to map the corresponding genes to 1q41-q42.1 by fluorescence in situ hybridization. The HB9 gene was later found to map to chromosome 7 (Ross et al., 1998).
In affected members of a previously reported sacral agenesis syndrome (176450) family from northern England (Lynch et al., 1995), Ross et al. (1998) found heterozygosity for deletion of an A from an AA dinucleotide at positions 652-653 of the HLXB9 gene.
In affected members of an Irish family with sacral agenesis syndrome (176450) previously reported by Lynch et al. (1995), Ross et al. (1998) found heterozygosity for a nonsense mutation at position 4213 in the homeobox, replacing glutamate codon 261 (CAG) with the TAG termination codon.
In affected members of a Norwegian family with sacral agenesis syndrome (176450), in which 5 members in 2 generations had severe anal stenosis requiring colostomy and 1 patient had the typical Currarino triad, Ross et al. (1998) found that affected members had a heterozygous deletion of a single cytosine from a stretch of 4 cytosines at positions 414-417 in the HLXB9 gene. Some members of this family were asymptomatic but showed sacral abnormalities by x-ray. Several had chronic constipation.
Ross et al. (1998) demonstrated heterozygosity for the HLXB9 gene in a sporadic American case of sacral agenesis (176450). The woman presented with presacral teratoma, severe anal stenosis, and spinal cord tethering. A de novo nonsense mutation in exon 1, a C-to-A transversion at nucleotide 575, resulted in replacement of tyrosine codon 166 (TAC) with a stop codon (TAA).
In an American kindred with sacral agenesis (176450), Ross et al. (1998) found that affected individuals had a heterozygous frameshift insertion of a cytosine into a stretch of 6 cytosines at positions 125-130 in exon 1 of the HLXB9 gene. The first presumably affected member in this family (with 3 affected children out of 4) had constipation but normal sacral x-ray. One member of the family had undeveloped coccyx and urinary tract bilateral ureteropelvic junction obstruction. Several were born with imperforate anus and anterior meningocele, as well as typical sickle-shaped hemisacrum revealed by x-ray. Rectovaginal fistula and vesicoureteric reflux resulted in the need for renal transplantation in one case.
In a 3-generation German family with autosomal dominant sacral agenesis, Kochling et al. (2001) found the 125insC frameshift mutation in the HLXB9 gene. Haplotype analysis in this and 2 previously reported families with the same mutation (Ross et al., 1998; Hagan et al., 2000) revealed different haplotypes in each of the 3 families, suggesting a recurrent mutation.
In affected members of a British family with autosomal dominant sacral agenesis (176450), Ross et al. (1998) found a heterozygous splice site mutation in the HLXB9 gene, replacing the conserved AG at the 3-prime end of intron 2 (positions 4889-4890) with GG. Clinical features in this family included severe anal stenosis requiring anal dilatation, presacral mass (anterior meningocele), imperforate anus, meningitis, and anterior ectopic anus and anal cysts. Some members of the family were asymptomatic, but x-rays revealed sacral abnormalities (the typical scimitar sacrum).
In a female patient with rectoperineal fistula and decreased bladder capacity in association with hemisacrum (176450), Belloni et al. (2000) found a heterozygous splice site mutation in exon 2 (858+1G-A).
In a female patient with hemisacrum and rectoperineal fistula (176450), Belloni et al. (2000) found a heterozygous thr248-to-ser amino acid mutation due to a single nucleotide substitution in exon 2 of the HLXB9 gene.
In affected members of a 3-generation family segregating Currarino syndrome (176450), Urioste et al. (2004) identified a heterozygous 24-bp deletion followed by an insertion of 2 bp (AG) at nucleotide 577 in exon 1 of the HLXB9 gene. The mutation was identified in the proband, a 22-year-old male in whom malignant transformation of a presacral teratoma was observed, as well as in 8 other family members, 3 of whom were asymptomatic but were subsequently found to have presacral teratomas. Of the 9 family members with the mutation, 7 had teratomas, 1 had a presacral 'tumor' removed 15 years previously, and 1 had a presacral mass but refused removal. Only 2 affected members displayed the complete triad.
In affected members of a 4-generation family with Currarino syndrome (176450), Wang et al. (2006) identified heterozygosity for a 4282G-T transversion in the HLXB9 gene, resulting in a glu283-to-ter (E283X) substitution in the DNA-binding domain. The mutation segregated with the disease and was not found in 5 unaffected family members.
Belloni, E., Martucciello, G., Verderio, D., Ponti, E., Seri, M., Jasonni, V., Torre, M., Ferrari, M., Tsui, L.-C., Scherer, S. W. Involvement of the HLXB9 homeobox gene in Currarino syndrome. (Letter) Am. J. Hum. Genet. 66: 312-319, 2000. [PubMed: 10631160] [Full Text: https://doi.org/10.1086/302723]
Catala, M. Genetic control of caudal development. Clin. Genet. 61: 89-96, 2002. [PubMed: 11940082] [Full Text: https://doi.org/10.1034/j.1399-0004.2002.610202.x]
Deguchi, Y., Kehrl, J. H. Selective expression of two homeobox genes in CD34-positive cells from human bone marrow. Blood 78: 323-328, 1991. [PubMed: 1712647]
Hagan, D. M., Ross, A. J., Strachan, T., Lynch, S. A., Ruiz-Perez, V., Wang, Y. M., Scambler, P., Custard, E., Reardon, W., Hassan, S., Nixon, P., Papapetrou, C., and 13 others. Mutation analysis and embryonic expression of the HLXB9 Currarino syndrome gene. Am. J. Hum. Genet. 66: 1504-1515, 2000. Note: Erratum: Am. J. Hum. Genet. 67: 769 only, 2000. [PubMed: 10749657] [Full Text: https://doi.org/10.1086/302899]
Harrison, K. A., Druey, K. M., Deguchi, Y., Tuscano, J. M., Kehrl, J. H. A novel human homeobox gene distantly related to proboscipedia is expressed in lymphoid and pancreatic tissues. J. Biol. Chem. 269: 19968-19975, 1994. [PubMed: 7914194]
Harrison, K. A., Thaler, J., Pfaff, S. L., Gu, H., Kehrl, J. H. Pancreas dorsal lobe agenesis and abnormal islets of Langerhans in Hlxb9-deficient mice. Nature Genet. 23: 71-75, 1999. [PubMed: 10471502] [Full Text: https://doi.org/10.1038/12674]
Kochling, J., Karbasiyan, M., Reis, A. Spectrum of mutations and genotype-phenotype analysis in Currarino syndrome. Europ. J. Hum. Genet. 9: 599-605, 2001. [PubMed: 11528505] [Full Text: https://doi.org/10.1038/sj.ejhg.5200683]
Lynch, S. A., Bond, P. M., Copp, A. J., Kirwan, W. O., Nour, S., Balling, R., Mariman, E., Burn, J., Strachan, T. A gene for autosomal dominant sacral agenesis maps to the holoprosencephaly region at 7q36. Nature Genet. 11: 93-95, 1995. [PubMed: 7550324] [Full Text: https://doi.org/10.1038/ng0995-93]
Najfeld, V., Menninger, J., Ballard, S. G., Deguchi, Y., Ward, D. C., Kehrl, J. H. Two diverged human homeobox genes involved in the differentiation of human hematopoietic progenitors map to chromosome 1, bands q41-42.1. Genes Chromosomes Cancer 5: 343-347, 1992. [PubMed: 1283323] [Full Text: https://doi.org/10.1002/gcc.2870050410]
Ross, A. J., Ruiz-Perez, V., Wang, Y., Hagan, D.-M., Scherer, S., Lynch, S. A., Lindsay, S., Custard, E., Belloni, E., Wilson, D. I., Wadey, R., Goodman, F., Orstavik, K. H., Monclair, T., Robson, S., Reardon, W., Burn, J., Scambler, P., Strachan, T. A homeobox gene, HLXB9, is the major locus for dominantly inherited sacral agenesis. Nature Genet. 20: 358-361, 1998. [PubMed: 9843207] [Full Text: https://doi.org/10.1038/3828]
Urioste, M., Garcia-Andrade, M. C., Valle, L., Robledo, M., Gonzalez-Palacios, F., Mendez, R., Ferreiros, J., Nuno, J., Benitez, J. Malignant degeneration of presacral teratoma in the Currarino anomaly. Am. J. Med. Genet. 128A: 299-304, 2004. [PubMed: 15216552] [Full Text: https://doi.org/10.1002/ajmg.a.30028]
Wang, R. Y., Jones, J. R., Chen, S., Rogers, R. C., Friez, M. J., Schwartz, C. E., Graham, J. M., Jr. A previously unreported mutation in a Currarino syndrome kindred. Am. J. Med. Genet. 140A: 1923-1930, 2006. [PubMed: 16906559] [Full Text: https://doi.org/10.1002/ajmg.a.31420]