Alternative titles; symbols
HGNC Approved Gene Symbol: RFX6
Cytogenetic location: 6q22.1 Genomic coordinates (GRCh38) : 6:116,877,242-116,932,161 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 6q22.1 | Mitchell-Riley syndrome | 615710 | Autosomal recessive | 3 |
RFX6 is a member of the regulatory factor X (RFX) family of transcription factors (see RFX1, 600006) (Aftab et al., 2008).
By database analysis to search for sequences containing the RFX DNA-binding domain (DBD), Aftab et al. (2008) identified RFX6 and 5 corresponding mammalian orthologs. The deduced 928-amino acid protein is a member of the winged helix family of DNA-binding proteins with high similarity over the DBDs and highest overall similarity to RFX4 (603958). RFX6 contains a winged helix region, predicted to interact with the major groove of DNA, and a conserved helix H3 predicted to interact with the minor groove. EST database analysis showed expression of RFX6 primarily in pancreas with lower expression in liver, which was confirmed by analysis of mouse SAGE libraries.
Aftab et al. (2008) determined that the RFX6 gene contains 19 exons.
By database analysis, Aftab et al. (2008) mapped the RFX6 gene to chromosome 6q22.2.
By large-scale yeast 2-hybrid proteome analysis of protein interactions, Aftab et al. (2008) determined that RFX6 interacted with RFX family members RFX2 (142765) and RFX3 (601337), in addition to interactions with DTX1 (602582), DTX2 (613141), FHL3 (602790), CCNK (603544), and SS18L1 (606472).
Smith et al. (2010) demonstrated that the transcription factor Rfx6 in mice directs islet cell differentiation downstream of Neurog3 (604882). Mice lacking Rfx6 failed to generate any of the normal islet cell types, except for pancreatic polypeptide-producing cells.
Huang et al. (2014) found that an evolutionarily conserved region in intron 4 of the RFX6 gene functions as a transcriptional enhancer with allele-specific activity. The T allele of a single-nucleotide polymorphism (SNP) in the region, rs339331, enhances HOXB13 (604607) chromatin binding and drives allele-specific upregulation of RFX6.
To identify early disease-driving events in type 2 diabetes (T2D; see 125853), Walker et al. (2023) performed traditional and multiplexed pancreatic tissue imaging, sorted islet cell transcriptomics, and islet cell functional analysis of early-stage T2D and control donors. By integrating diverse modalities, Walker et al. (2023) showed that early-stage T2D is characterized by beta cell-intrinsic defects that could be divided into different gene regulatory modules. They identified RFX6 as a beta-cell hub gene and showed multiple layers of genetic risk that converge on an RFX6-mediated network to reduce insulin secretion by beta cells. RFX6 expression is reduced in T2D.
Mitchell-Riley Syndrome
Smith et al. (2010) analyzed the candidate gene RFX6 in 6 patients with neonatal diabetes, hypoplastic or annular pancreas, intestinal atresia and/or malrotation, and gallbladder hypoplasia or agenesis (Mitchell-Riley syndrome; MTCHRS; 615710), and identified homozygosity or compound heterozygosity for RFX6 mutations in 5 of the 6 probands (612659.0001-612659.0006). The authors noted that the 3 patients with mutations resulting in complete loss of function died within the first few months of life, whereas the 2 patients with mutations associated with residual function were still alive at 4.5 and 9 years, respectively.
In two 9-year-old Turkish double first cousins with Mitchell-Riley syndrome, Sansbury et al. (2015) identified compound heterozygosity for 2 nonsense mutations in the RFX6 gene (R726X, 612659.0007; R866X, 612659.0008). Noting that the 2 affected cousins exhibited a relatively milder phenotype than previously reported patients, the authors suggested that their mutations might result in incomplete inactivation of RFX6.
Prostate Cancer Susceptibility
Huang et al. (2014) found that a prostate cancer (176807) risk-associated SNP on chromosome 6q22, rs339331, lies within an evolutionarily conserved region in intron 4 of the transcription factor RFX6 gene that functions as a HOXB13-binding site. The risk-associated T allele at rs339331 increases binding of HOXB13 to a transcriptional enhancer, conferring allele-specific upregulation of RFX6. Suppression of RFX6 diminishes prostate cancer cell proliferation, migration, and invasion. Clinical data indicated that RFX6 upregulation in human prostate cancers correlates with tumor progression, metastasis, and risk of biochemical relapse. Huang et al. (2014) observed a significant association between the risk-associated T allele at rs339331 and increased RFX6 mRNA levels in human prostate tumors. The authors concluded that rs339331 affects prostate cancer risk by altering RFX6 expression through a functional interaction with the prostate cancer susceptibility gene HOXB13.
Associations Pending Confirmation
Patel et al. (2017) sequenced a cohort of European patients with maturity-onset diabetes of the young (MODY; see 606391) and compared them with population controls. In the discovery cohort of 36 patients, 2 unrelated probands were identified with heterozygous nonsense variants in RFX6. Patel et al. (2017) found that RFX6 protein truncating variants were enriched in the MODY discovery and replication cohorts compared to the European control population within ExAC (odds ratio (OR) = 131, p = 1 x 10(-4)) and found similar results in replication cohorts of 348 non-Finnish European individuals (OR = 43, p = 5 x 10(-5)) and 80 Finnish individuals (OR = 22, p = 1 x 10(-6)). MODY segregated with variants reported in the 2 families, but with later age at onset (32, range 24 to 46) and incomplete penetrance compared with other causes of MODY. The hyperglycemia was associated with beta-cell dysfunction and was associated with lower levels of gastric inhibitory polypeptide (GIP; 137240) in the fasted and stimulated state.
Smith et al. (2010) generated Rfx6-null mice. They also generated mice in which the Rfx6 locus is marked by beta-galactosidase expression, and these studies showed that Rfx6 is initially expressed broadly in the definitive endoderm after gastrulation and becomes restricted to the gut and pancreatic bud at midgestation. Furthermore, Rfx6 is reactivated by Neurog3 in islet progenitor cells and is also restricted to pancreatic islets in the mature pancreas. Rfx6-null mice were born at the expected mendelian ratio, but failed to feed normally, exhibited gross bowel distention to small bowel obstruction, and died within 2 days postpartum. Some of the Rfx6-null mice also had reduced pancreas size. To test for effects on gene expression before birth, Smith et al. (2010) collected RNA from embryonic day 17.5 pancreata, and showed that the null mice had almost no expression of islet hormone genes, except for pancreatic polypeptide (Ppy).
In a female infant, born of consanguineous Pakistani parents, with neonatal diabetes, duodenal and jejunal atresia, annular pancreas, and gallbladder agenesis (MTCHRS; 615710), originally reported by Mitchell et al. (2004) as 'family 1,' Smith et al. (2010) identified homozygosity for a +2T-C transition at the donor splice site in intron 2 of the RFX6 gene. The unaffected parents were heterozygous for the mutation. Amplification of RFX6 mRNA from autopsy pancreas from the patient, who died of multiorgan failure at 6.5 months of life, demonstrated that there was no normally spliced transcript, and no RNA was detected from exons 1 and 2, upstream of the splicing mutation, consistent with nonsense-mediated decay. The patient's similarly affected deceased older brother, who had neonatal diabetes, patent foramen ovale, duodenal and jejeunal atresia, and hypoplastic pancreas and gallbladder, died at 5 months of age with multiorgan failure.
In a female infant who was conceived by in vitro fertilization with a donated egg and had neonatal hyperglycemia, duodenal web with malrotation, and hypoplastic pancreas and gallbladder (MTCHRS; 615710), originally reported by Mitchell et al. (2004), Smith et al. (2010) identified compound heterozygosity for splice site mutations in the RFX6 gene: a -12A-G transition at the acceptor site in intron 1 and a +2T-G transversion at the donor site in intron 6 (612659.0003). The patient was alive at 9 years of age and intermittently off insulin.
For discussion of the +2T-G transversion at the donor site in intron 6 of the RFX6 gene that was found in a patient with Mitchell-Riley syndrome (MTCHRS; 615710) by Smith et al. (2010), see 612659.0002.
In a Pakistani girl, born to first-cousin parents, who had neonatal diabetes, duodenal atresia, gallbladder agenesis, and an anteriorly placed anus (MTCHRS; 615710), previously reported by Chappell et al. (2008), Smith et al. (2010) identified homozygosity for a ser217-to-pro (S217P) substitution in exon 5 of the RFX6 gene, at a highly conserved residue between the DNA-binding and dimerization domains. Functional analysis showed that S217P only modestly reduced DNA binding and did not affect dimer formation. The patient, who had no pancreatic abnormality by ultrasound, was alive at 4.5 years and insulin dependent. The unaffected parents were heterozygous for the mutation.
In a male infant, born to consanguineous parents of Moroccan descent, who had congenital hemochromatosis, neonatal diabetes, duodenal and jejunal atresia, intestinal malrotation, hypoplastic pancreas, and gallbladder agenesis (MTCHRS; 615710), originally reported by Martinovici et al. (2010), Smith et al. (2010) identified homozygosity for an arg181-to-gln (R181Q) substitution in exon 4 of the RFX6 gene. Functional analysis demonstrated that the R181Q mutation, which alters a highly conserved amino acid in the DNA-binding domain, completely abrogates DNA binding. The patient died in the third month of life. Both the mother, who had insulin-dependent diabetes, and the father, who had impaired fasting glucose, were heterozygous for the mutation.
In a male infant, born to nonconsanguineous parents, who had intrauterine growth retardation and duodenal atresia and was diagnosed with neonatal diabetes on day 2 of life (MTCHRS; 615710), Smith et al. (2010) identified homozygosity for an out-of-frame 13-bp deletion encompassing the last 5 nucleotides of exon 7 and the first 8 nucleotides of intron 7 of the RFX6 gene. The patient had a complicated course and died of gastrointestinal hemorrhage at 2.5 months of age. Both the mother, who had gestational diabetes during the pregnancy, and the father, who had been diagnosed with type 1 diabetes, were heterozygous for the mutation.
In two 9-year-old Turkish double first cousins with Mitchell-Riley syndrome (MTCHRS; 615710), Sansbury et al. (2015) identified compound heterozygosity for 2 mutations in the RFX6 gene: a c.2176C-T transition in exon 17, resulting in an arg726-to-ter (R726X) substitution, and a c.2596C-T transition in exon 18, resulting in an arg866-to-ter (R866X; 612659.0008) substitution. The 4 parents were each heterozygous for 1 of the mutations. Noting that the 2 affected cousins exhibited a relatively milder phenotype than previously reported patients, including later onset of diabetes, no liver pathology apart from absent gallbladder in 1 patient, and a greater age of survival, the authors suggested that their mutations might result in incomplete inactivation of RFX6.
For discussion of the c.2596C-T transition in exon 18 of the RFX6 gene, resulting in an arg866-to-ter (R866X) substitution, that was found in compound heterozygous state in 2 Turkish cousins with Mitchell-Reilly syndrome (MTCHRS; 615710) by Sansbury et al. (2015), see 612659.0007.
Aftab, S., Semenec, L., Chu, J. S.-C., Chen, N. Identification and characterization of novel human tissue-specific RFX transcription factors. BMC Evol. Biol. 8: 226, 2008. Note: Electronic Article. [PubMed: 18673564] [Full Text: https://doi.org/10.1186/1471-2148-8-226]
Chappell, L., Gorman, S., Campbell, F., Ellard, S., Rice, G., Dobbie, A., Crow, Y. A further example of a distinctive autosomal recessive syndrome comprising neonatal diabetes mellitus, intestinal atresias and gall bladder agenesis. Am. J. Med. Genet. 146A: 1713-1717, 2008. [PubMed: 18512226] [Full Text: https://doi.org/10.1002/ajmg.a.32304]
Huang, Q., Whitington, T., Gao, P., Lindberg, J. F., Yang, Y., Sun, J., Vaisanen, M.-R., Szulkin, R., Annala, M., Yan, J., Egevad, L. A., Zhang, K., and 10 others. A prostate cancer susceptibility allele at 6q22 increases RFX6 expression by modulating HOXB13 chromatin binding. Nature Genet. 46: 126-135, 2014. [PubMed: 24390282] [Full Text: https://doi.org/10.1038/ng.2862]
Martinovici, D., Ransy, V., Eijnden, S. V., Ridremont, C., Pardou, A., Cassart, M., Avni, F., Donner, C., Lingier, P., Mathieu, A., Gulbis, B., De Brouckere, V., Cnop, M., Abramowicz, M., Desir, J. Neonatal hemochromatosis and Martinez-Frias syndrome of intestinal atresia and diabetes mellitus in a consanguineous newborn. Europ. J. Med. Genet. 53: 25-28, 2010. [PubMed: 19887127] [Full Text: https://doi.org/10.1016/j.ejmg.2009.10.004]
Mitchell, J., Punthakee, Z., Lo, B., Bernard, C., Chong, K., Newman, C., Cartier, L., Desilets, V., Cutz, E., Hansen, I. L., Riley, P., Polychronakos, C. Neonatal diabetes, with hypoplastic pancreas, intestinal atresia and gall bladder hypoplasia: search for the aetiology of a new autosomal recessive syndrome. Diabetologia 47: 2160-2167, 2004. [PubMed: 15592663] [Full Text: https://doi.org/10.1007/s00125-004-1576-3]
Patel, K. A., Kettunen, J., Laakso, M., Stancakova, A., Laver, T. W., Colclough, K., Johnson, M. B., Abramowicz, M., Groop, L., Miettinen, P. J., Shepherd, M. H., Flanagan, S. E., Ellard, S., Inagaki, N., Hattersley, A. T., Tuomi, T., Cnop, M., Weedon, M. N. Heterozygous RFX6 protein truncating variants are associated with MODY with reduced penetrance. Nature Commun. 8: 888, 2017. [PubMed: 29026101] [Full Text: https://doi.org/10.1038/s41467-017-00895-9]
Sansbury, F. H., Kirel, B., Caswell, R., Allen, H. L., Flanagan, S. E., Hattersley, A. T., Ellard, S., Shaw-Smith, C. J. Biallelic RFX6 mutations can cause childhood as well as neonatal onset diabetes mellitus. Europ. J. Hum. Genet. 23: 1744-1748, 2015. Note: Erratum: Europ. J. Hum. Genet. 23: 1750 only, 2015. [PubMed: 26264437] [Full Text: https://doi.org/10.1038/ejhg.2015.161]
Smith, S. B., Qu, H.-Q., Taleb, N. Kishimoto, N. Y., Scheel, D. W., Lu, Y., Patch, A.-M., Grabs, R., Wang, J., Lynn, F. C., Miyatsuka, T., Mitchell, J., and 16 others. Rfx6 directs islet formation and insulin production in mice and humans. Nature 463: 775-780, 2010. [PubMed: 20148032] [Full Text: https://doi.org/10.1038/nature08748]
Walker, J. T., Saunders, D. C., Rai, V., Chen, H.-H., Orchard, P., Dai, C., Pettway, Y. D., Hopkirk, A. L., Reihsmann, C. V., Tao, Y., Fan, S., Shrestha, S., and 21 others. Genetic risk converges on regulatory networks mediating early type 2 diabetes. Nature 624: 621-629, 2023. [PubMed: 38049589] [Full Text: https://doi.org/10.1038/s41586-023-06693-2]