Alternative titles; symbols
HGNC Approved Gene Symbol: DIAPH1
SNOMEDCT: 1172900005;
Cytogenetic location: 5q31.3 Genomic coordinates (GRCh38): 5:141,515,021-141,619,000 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 5q31.3 | Deafness, autosomal dominant 1, with or without thrombocytopenia | 124900 | Autosomal dominant | 3 |
| Seizures, cortical blindness, microcephaly syndrome | 616632 | Autosomal recessive | 3 |
The DIAPH1 gene encodes a protein that plays a role in the regulation of cell morphology and cytoskeletal organization (summary by Al-Maawali et al., 2016).
In a large Costa Rican kindred with autosomal dominant, fully penetrant, nonsyndromic sensorineural progressive low-frequency hearing loss (DFNA1; 124900), Lynch et al. (1997) mapped the disease gene to a region on chromosome 5q31 by linkage analysis. They constructed a complete 800-kb bacterial artificial chromosome (BAC) contig of the linked region and identified DIAPH1, a human gene homologous to the Drosophila gene 'diaphanous.' This human homolog of diaphanous has approximately 3,800 bp of coding sequence and a 3-prime untranslated region (UTR) of 918 or 1,891 bp. Lynch et al. (1997) found that the human gene is expressed in brain, heart, placenta, lung, kidney, pancreas, liver, and skeletal muscle. A single transcript of 4.7 kb was observed in all tissues, with highest expression in skeletal muscle. They confirmed expression of the diaphanous homolog in the cochlea by RT-PCR of cochlear RNA. In the course of cloning the DIAPH1 gene, Lynch et al. (1997) identified a second human homolog of the Drosophila diaphanous gene, DIAPH2 (300108), which maps to Xq22.
Ercan-Sencicek et al. (2015) found expression of the DIAPH1 gene in the developing mouse and human forebrain and in neural progenitor cells. During embryogenesis, DIAPH1 was expressed in ventricular and subventricular zone progenitor cells of the dorsal and ventral forebrain and the brainstem. During postnatal development, DIAPH1 expression was detected in the cerebral cortex, basal ganglia, hippocampus, thalamus, and external granular layer of the cerebellum. DIAPH1 colocalized with centrosomal proteins, centrosomes, and mitotic spindles.
Neuhaus et al. (2017) found expression of the Diaph1 gene in the organ of Corti in the mouse cochlea. It was specifically expressed in the inner pillar hair cells as well as at the base of the outer hair cells and in outer pillar cells. Diaph1 was also expressed in neuronal structures in the ear, including spiral ganglion neurons and the cochlear nerve, where it was associated with oligodendrocytes.
Actin polymerization involves proteins known to interact with diaphanous protein in Drosophila and mouse. Lynch et al. (1997) speculated that the biologic role of DIAPH1 in hearing is likely to be the regulation of actin polymerization in hair cells of the inner ear. Given that human DIAPH1 appears to be ubiquitously expressed, and that the only observed phenotype in the Costa Rican family with a DIAPH1 mutation (see MOLECULAR GENETICS) is hearing loss, it seemed likely to Lynch et al. (1997) that the hair cells of the cochlea are particularly sensitive to proper maintenance of the actin cytoskeleton.
Geneste et al. (2002) found that LIM domain kinase-1 (LIMK1; 601329) and diaphanous cooperated to regulate serum response factor (SRF; 600589) and actin dynamics in a rat neural precursor cell line.
Tsuji et al. (2002) found that treatment of serum-starved Swiss 3T3 fibroblasts with specific inhibitors of the Rho (see 165390) downstream effectors Rock (ROCK1; 601702) and Dia1 suppressed formation of LPA-induced stress fibers and focal adhesions. Inhibition of Rock, but not Dia1, also induced membrane ruffles and focal complexes. Rock activation resulted in tyrosine phosphorylation of focal adhesion kinase (FAK, or PTK2; 600758) and paxillin (PXN; 602505), whereas DIA1 activation resulted in phosphorylation of Cas (BCAR1; 602941), followed by activation of Rac (RAC1; 602048). In addition, Rock antagonized Rac activation.
Using human melanocytes and melanoma cell lines, Carreira et al. (2006) identified MITF (156845) as a regulator of DIAPH1. Since DIAPH1 also regulates SKP2 (601436), an F-box protein that promotes degradation of p27(Kip1) (CDKN1B; 600778), depletion of MITF led to downregulation of DIAPH1, followed by p27(Kip1)-dependent G1 arrest, reorganization of the actin cytoskeleton, and increased cellular invasiveness. In contrast, increased MITF expression promoted proliferation. Carreira et al. (2006) concluded that variations in environmental cues that determine MITF activity dictate the differentiation, proliferative, and invasive/migratory potential of melanoma cells.
Fan et al. (2010) found that, like RHOA (165390), activated human RIF (RHOF; 618867) triggered formation of actin stress fibers in epithelial cells by interacting with DIAPH1. Induction of stress fibers by RIF was also dependent on ROCK1 activity. In the absence of DIAPH1, RIF-induced stress fibers were lost and RIF-induced filopodia changed to bleb-like structures, suggesting that DIAPH1 plays a role in maintaining the integrity of these structures.
Crystal Structure
Rose et al. (2005) presented the crystal structure of RhoC (165380) in complex with the regulatory N terminus of mouse Diaph1 containing the GBD/FH3 region, an all-helical structure with armadillo repeats. Rho uses its 'switch' regions for interacting with 2 subdomains of GBD/FH3. Rose et al. (2005) showed that the FH3 domain of Diaph1 forms a stable dimer and identified the diaphanous autoregulatory domain (DAD)-binding site. Although binding of Rho and DAD on the N-terminal fragment of Diaph1 are mutually exclusive, their binding sites are only partially overlapping.
Lynch et al. (1997) determined that the DIAPH1 gene contains at least 18 exons.
By BAC analysis, Lynch et al. (1997) mapped the DIAPH1 gene to chromosome 5q31.
Autosomal Dominant Deafness 1 with or without Thrombocytopenia
In affected members of a large Costa Rican kindred with autosomal dominant deafness-1 (DFNA1; 124900), Lynch et al. (1997) identified a splice donor mutation in the penultimate exon of the DIAPH1 gene (602121.0001).
In 8 affected individuals from 2 unrelated families with DFNA1 with thrombocytopenia (see DFNA1, 124900), Stritt et al. (2016) identified a heterozygous truncating mutation in the DIAPH1 gene (R1213X; 602121.0005). The mutation, which was found by high-throughput sequencing and confirmed by Sanger sequencing, segregated with the disorder in both families. Megakaryocytes derived from 1 of the patients showed defective maturation and defective proplatelet formation compared to controls. Mutant platelets also showed an altered cytoskeleton with disorganized microtubules, aberrant organization of F-actin, increased microtubule content, and increased microtubule stability. Stritt et al. (2016) hypothesized that the R1213X mutation results in constitutive activation of DIAPH1 with cytoskeletal defects causing reduced proplatelet formation.
In affected members of 2 unrelated families with DFNA1 with thrombocytopenia, Neuhaus et al. (2017) identified heterozygous truncating mutations in exon 27 of the DIAPH1 gene, R1213X and a 2-bp deletion (602121.0006). The mutation in the first family was found by next-generation sequencing and confirmed by Sanger sequencing; the mutation in the second family was found by targeted Sanger sequencing of the DIAPH1 gene. Functional studies of the variants were not performed, but Neuhaus et al. (2017) hypothesized that since the mutation occurs in the penultimate exon, the mutant transcript likely escapes nonsense-mediated mRNA decay, resulting in the production of a truncated protein with a gain-of-function effect.
In affected members of a Japanese family segregating autosomal dominant deafness and thrombocytopenia, Ganaha et al. (2017) identified heterozygosity for the R1213X mutation in the DIAPH1 gene. The mutation, which was identified by next-generation sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family.
Seizures, Cortical Blindness, and Microcephaly Syndrome
In 5 sibs, born of consanguineous Saudi Arabian parents, with seizures, cortical blindness, and microcephaly syndrome (SCBMS; 616632), Ercan-Sencicek et al. (2015) identified a homozygous truncating mutation in the DIAPH1 gene (Q778X; 602121.0002). The mutation, which was found by a combination of linkage analysis and whole-exome sequencing, segregated with the disorder in the family.
Al-Maawali et al. (2016) identified 2 different homozygous truncating mutations in the DIAPH1 gene (602121.0003 and 602121.0004) in 4 patients from 2 unrelated consanguineous Arab families with SCBMS. None of the patients or parents in the families reported by Ercan-Sencicek et al. (2015) or Al-Maawali et al. (2016) were reported to have deafness.
Ercan-Sencicek et al. (2015) found that mice with homozygous deletion of the Diaph1 gene developed unilateral dilatation of the ventricles without blockage of the cerebral aqueduct. However, mutant mice did not have microcephaly or hypoplasia of the corpus callosum, and absence of Diaph1 did not grossly alter the organization of actin filaments or tubulin.
In members of a large kindred of Costa Rica affected with DFNA1 (124900), Lynch et al. (1997) demonstrated a guanine-to-thymine transversion in the splice donor of the penultimate exon of the human diaphanous homolog on chromosome 5q31. The substitution disrupted the canonical splice donor sequence AAGgtaagt and resulted in insertion of 4 nucleotides in the gene transcript of affected individuals. The mechanism for the insertion was splicing at a cryptic site 4 bp 3-prime of the wildtype site. The insertion leads to a frameshift, encoding 21 aberrant amino acids, followed by protein termination that truncated 32 amino acids from the mature protein. The sequence of the RT-PCR product from cochlear RNA was wildtype. Hence, if alternate splice forms of the gene exist, normal cochlear transcripts include the region of the gene that is improperly spliced in affected members of the kindred. Lynch et al. (1997) noted that the DFNA1 mutation in the Costa Rican family is relatively subtle, in that it affects only the C-terminal 52 amino acids of a protein that must have more than 1,200 amino acid residues. The mutation may represent a partial loss of function of the gene.
In 5 sibs (family SAR1008), born of consanguineous Saudi Arabian parents, with seizures, cortical blindness, and microcephaly syndrome (SCBMS; 616632) Ercan-Sencicek et al. (2015) identified a homozygous c.2332C-T transition (c.2332C-T, chr5.140,953,085) in the DIAPH1 gene, resulting in a gln778-to-ter (Q778X) substitution predicted to result in a truncated protein lacking a conserved domain responsible for the generation of linear actin filaments. The mutation, which was found by a combination of linkage analysis and whole-exome sequencing, segregated with the disorder in the family. Patient cells showed a 4-fold decrease in DIAPH1 expression compared to controls, consistent with nonsense-mediated mRNA and a complete loss of function.
In a boy (family MC2500) , born of consanguineous Arab parents, with seizures, cortical blindness, and microcephaly syndrome (SCBMS; 616632), Al-Maawali et al. (2016) identified a homozygous 1-bp deletion (c.2769delT, NM_005219.4) in the DIAPH1 gene, resulting in a frameshift and premature termination (Phe923fsTer). The mutation, which was found by exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family and was not found in the Exome Variant Server or ExAC databases or in 1,200 in-house control exomes. Although studies of patient cells and functional studies were not performed, the nature of the mutation was consistent with a loss of protein function.
In 3 sibs (family MC36500), born of consanguineous Arab parents, with seizures, cortical blindness, and microcephaly syndrome (SCBMS; 616632) Al-Maawali et al. (2016) identified a homozygous c.3145C-T transition (c.3145C-T, NM_005219.4) in the DIAPH1 gene, resulting in an arg1049-to-ter (R1049X) substitution. The mutation, which was found by exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family and was not found in the Exome Variant Server or ExAC databases or in 1,200 in-house control exomes. Although studies of patient cells and functional studies were not performed, the nature of the mutation was consistent with a loss of protein function.
In 8 affected individuals from 2 unrelated families with autosomal dominant deafness-1 with thrombocytopenia (see DFNA1, 124900), Stritt et al. (2016) identified a heterozygous c.3637C-T transition (c.3637C-T, ENST00000398557) in exon 27 of the DIAPH1 gene, resulting in an arg1213-to-ter (R1213X) substitution within the DAD autoregulatory domain. The mutation, which was found by high-throughput sequencing and confirmed by Sanger sequencing, segregated with the disorder in both families. It was not found in the ExAC database or in 4,151 exomes of an in-house database. Megakaryocytes derived from 1 of the patients showed defective maturation and defective proplatelet formation compared to controls. Patient platelets showed abnormal localization of the mutant DIAPH1 protein throughout the cytoplasm rather than to the peripheral marginal band as observed in control platelets. Mutant platelets also showed an altered cytoskeleton with disorganized microtubules, aberrant organization of F-actin, increased microtubule content, and increased microtubule stability. Similar abnormalities were observed in cells transfected with the mutation. Stritt et al. (2016) hypothesized that the R1213X mutation results in constitutive activation of DIAPH1 with cytoskeletal defects causing reduced proplatelet formation.
Neuhaus et al. (2017) identified a heterozygous R1213X mutation in the DIAPH1 gene (c.3637C-T, NM_005219.4) in a father and son with DFNA1 with thrombocytopenia. The mutation was found by targeted Sanger sequencing. Functional studies of the variant were not performed, but Neuhaus et al. (2017) noted that since the mutation occurs in the penultimate exon, the mutant transcript likely escapes nonsense-mediated mRNA decay, resulting in the production of a truncated protein with a gain-of-function effect.
In affected members of a Japanese family segregating autosomal dominant deafness and thrombocytopenia, Ganaha et al. (2017) identified heterozygosity for the R1213X mutation in the DIAPH1 gene. The mutation, which was identified by next-generation sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family.
In 5 members of a 3-generation family with autosomal dominant deafness-1 with thrombocytopenia (see DFNA1; 124900), Neuhaus et al. (2017) identified a heterozygous 2-bp deletion (c.3624_3625delAG, NM_005219.4) in exon 27 of the DIAPH1 gene, resulting in a frameshift and premature termination (Ala1210SerfsTer31). The mutation, which was found by next-generation sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. Functional studies of the variant were not performed, but Neuhaus et al. (2017) hypothesized that since the mutation occurred in the penultimate exon, the mutant transcript likely escapes nonsense-mediated mRNA decay, resulting in the production of a truncated protein with a gain-of-function effect.
Al-Maawali, A., Barry, B. J., Rajab, A., El-Quessny, M., Seman, A., Coury, S. N., Barkovich, A. J., Yang, E., Walsh, C. A., Mochida, G. H., Stoler, J. M. Novel loss-of-function variants in DIAPH1 associated with syndromic microcephaly, blindness, and early onset seizures. Am. J. Med. Genet. 170A: 435-440, 2016. [PubMed: 26463574] [Full Text: https://doi.org/10.1002/ajmg.a.37422]
Carreira, S., Goodall, J., Denat, L., Rodriguez, M., Nuciforo, P., Hoek, K. S., Testori, A., Larue, L., Goding, C. R. Mitf regulation of Dia1 controls melanoma proliferation and invasiveness. Genes Dev. 20: 3426-3439, 2006. [PubMed: 17182868] [Full Text: https://doi.org/10.1101/gad.406406]
Ercan-Sencicek, A. G., Jambi, S., Franjic, D., Nishimura, S., Li, M., El-Fishawy, P., Morgan, T. M., Sanders, S. J., Bilguvar, K., Suri, M., Johnson, M. H., Gupta, A. R., Yuksel, Z., Mane, S., Grigorenko, E., Picciotto, M., Alberts, A. S., Gunel, M., Sestan, N., State, M. W. Homozygous loss of DIAPH1 is a novel cause of microcephaly in humans. Europ. J. Hum. Genet. 23: 165-172, 2015. [PubMed: 24781755] [Full Text: https://doi.org/10.1038/ejhg.2014.82]
Fan, L., Pellegrin, S., Scott, A., Mellor, H. The small GTPase Rif is an alternative trigger for the formation of actin stress fibers in epithelial cells. J. Cell Sci. 123: 1247-1252, 2010. [PubMed: 20233848] [Full Text: https://doi.org/10.1242/jcs.061754]
Ganaha, A., Kaname, T., Shinjou, A., Chinen, Y., Yanagi, K., Higa, T., Kondu, S., Suzuki, M. Progressive macrothrombocytopenia and hearing loss in a large family with DIAPH1 related disease. Am. J. Med. Genet. 173A: 2826-2830, 2017. [PubMed: 28815995] [Full Text: https://doi.org/10.1002/ajmg.a.38411]
Geneste, O., Copeland, J. W., Treisman, R. LIM kinase and Diaphanous cooperate to regulate serum response factor and actin dynamics. J. Cell Biol. 157: 831-838, 2002. [PubMed: 12034774] [Full Text: https://doi.org/10.1083/jcb.200203126]
Lynch, E. D., Lee, M. K., Morrow, J. E., Welcsh, P. L., Leon, P. E., King, M.-C. Nonsyndromic deafness DFNA1 associated with mutation of the human homolog of the Drosophila gene diaphanous. Science 278: 1315-1318, 1997. [PubMed: 9360932]
Neuhaus, C., Lang-Roth, R., Zimmermann, U., Heller, R., Eisenberger, T., Weikert, M., Markus, S., Knipper, M., Bolz, H. J. Extension of the clinical and molecular phenotype of DIAPH1-associated autosomal dominant hearing loss (DFNA1). Clin. Genet. 91: 892-901, 2017. [PubMed: 27808407] [Full Text: https://doi.org/10.1111/cge.12915]
Rose, R., Weyand, M., Lammers, M., Ishizaki, T., Ahmadian, M. R., Wittinghofer, A. Structural and mechanistic insights into the interaction between Rho and mammalian Dia. (Letter) Nature 435: 513-518, 2005. [PubMed: 15864301] [Full Text: https://doi.org/10.1038/nature03604]
Stritt, S., Nurden, P., Turro, E., Greene, D., Jansen, S. B., Westbury, S. K., Petersen, R., Astle, W. J., Marlin, S., Bariana, T. K., Kostadima, M., Lentaigne, C. A gain-of-function variant in DIAPH1 causes dominant macrothrombocytopenia and hearing loss. Blood 127: 2903-2914, 2016. [PubMed: 26912466] [Full Text: https://doi.org/10.1182/blood-2015-10-675629]
Tsuji, T., Ishizaki, T., Okamoto, M., Higashida, C., Kimura, K., Furuyashiki, T., Arakawa, Y., Birge, R. B., Nakamoto, T., Hirai, H., Narumiya, S. ROCK and mDia1 antagonize in Rho-dependent Rac activation in Swiss 3T3 fibroblasts. J. Cell Biol. 157: 819-830, 2002. [PubMed: 12021256] [Full Text: https://doi.org/10.1083/jcb.200112107]