RESUMEN
Mental retardation and epilepsy often occur together. They are both heterogeneous conditions with acquired and genetic causes. Where causes are primarily genetic, major advances have been made in unraveling their molecular basis. The human X chromosome alone is estimated to harbor more than 100 genes that, when mutated, cause mental retardation. At least eight autosomal genes involved in idiopathic epilepsy have been identified, and many more have been implicated in conditions where epilepsy is a feature. We have identified mutations in an X chromosome-linked, Aristaless-related, homeobox gene (ARX), in nine families with mental retardation (syndromic and nonspecific), various forms of epilepsy, including infantile spasms and myoclonic seizures, and dystonia. Two recurrent mutations, present in seven families, result in expansion of polyalanine tracts of the ARX protein. These probably cause protein aggregation, similar to other polyalanine and polyglutamine disorders. In addition, we have identified a missense mutation within the ARX homeodomain and a truncation mutation. Thus, it would seem that mutation of ARX is a major contributor to X-linked mental retardation and epilepsy.
Asunto(s)
Proteínas de Drosophila/genética , Epilepsia/genética , Discapacidad Intelectual/genética , Mutación , Cromosoma X , Secuencia de Aminoácidos , Animales , Salud de la Familia , Femenino , Haplotipos , Humanos , Masculino , Ratones , Modelos Genéticos , Datos de Secuencia Molecular , Mutación Missense , Hibridación de Ácido Nucleico , Linaje , Poli A/genética , Homología de Secuencia de Aminoácido , Distribución Tisular , Transcripción GenéticaRESUMEN
The Omega class glutathione transferase GSTO1-1 can catalyze the reduction of pentavalent methylated arsenic species and is responsible for the biotransfomation of potentially toxic alpha-haloketones. We investigated the cause of GSTO1-1 deficiency in the T-47D breast cancer cell line and found that the cell line is hemizygous for a polymorphic allele that encodes the deletion of Glu155. Northern and Western blots show that T-47D cells contain GSTO1 mRNA but no GSTO1-1 protein suggesting that the deletion of Glu155 causes GSTO1-1 deficiency in vivo. In further support of this contention we found that lymphoblastoid cell lines from subjects who are heterozygous for the deletion of Glu155 have only 60% of normal activity with the GSTO1-1 specific substrate 4-nitrophenacyl glutathione. Pulse-chase studies showed that the deletion of Glu155 causes increased turnover of GSTO1-1 in T47-D cells. These data establish the fact that the polymorphic deletion of Glu155 can cause GSTO1-1 deficiency in vivo. GSTO1-1 expression is elevated in some cell lines that are resistant to the cytotoxic cancer drugs adriamycin, etoposide and cisplatinum but its specific contribution to multi drug resistance has not been evaluated. In this study GSTO1-1 deficient T47-D cells were used to determine if GSTO1-1 contributes directly to arsenic and drug resistance. We established stable expression of normal GSTO1-1 in T-47D cells and found that this did not alter sensitivity to arsenic trioxide, cisplatinum daunorubicin or etoposide.
Asunto(s)
Antineoplásicos/metabolismo , Arsenicales/metabolismo , Citotoxinas/metabolismo , Resistencia a Antineoplásicos , Ácido Glutámico/metabolismo , Glutatión Transferasa , Óxidos/metabolismo , Trióxido de Arsénico , Línea Celular Tumoral , Ensayos de Selección de Medicamentos Antitumorales , Genotipo , Glutatión Transferasa/deficiencia , Glutatión Transferasa/genética , Humanos , Polimorfismo GenéticoRESUMEN
The Human Genetics Society of Australasia is a vibrant professional society with more than 900 members that promotes and regulates the practice of human and medical genetics in Australia and New Zealand. The growth of human genetics was stimulated by the development of diagnostic clinical cytogenetics laboratories in the early to mid 1960s. This coincided with the recognition by medical specialists, mainly pediatricians, that genetic disorders, especially inborn errors of metabolism and birth defects, were of clinical interest and potentially challenging areas for their skills. The organization of professionals in human genetics was slow to evolve. There was an early Western Australian Human Genetics Society, and the cytogenetics community had begun to meet annually from about 1966 but was coordinated by a mailing list rather than as a formal organization. In 1976, as part of the celebrations of the Centenary Year of the Adelaide Children's Hospital, a clinical genetics meeting involving several high profile international speakers and most of the senior medical geneticists in Australia and New Zealand along with the annual meeting of the loose-knit cytogeneticists group agreed that a small working group be charged with setting up a Human Genetics Society. The society was formally incorporated in South Australia in 1977.
Asunto(s)
Genética Médica/historia , Sociedades/historia , Australasia , Citogenética/historia , Historia del Siglo XX , Historia del Siglo XXI , HumanosRESUMEN
Numerous cytogenetic and molecular studies of breast cancer have identified frequent loss of heterozygosity (LOH) of the long arm of human chromosome 16. On the basis of these data, the likely locations of breast cancer tumor suppressor genes are bands 16q22.1 and 16q24.3. We have mapped the CBFA2T3 (MTG16) gene, previously cloned as a fusion partner of the AML1 protein from a rare (16;21) leukemia translocation, to the 16q24.3 breast cancer LOH region. The expression of CBFA2T3 was significantly reduced in a number of breast cancer cell lines and in primary breast tumors, including early ductal carcinomas in situ, when compared with nontransformed breast epithelial cell lines and normal breast tissue. Reintroduction of CBFA2T3 into different breast tumor derived cell lines with decreased expression of this gene reduced colony growth on plastic and in soft agar. CBFA2T3 was shown to function as a transcriptional repressor when tethered to the GAL4 DNA-binding domain in a reporter gene assay and, therefore, has the potential to be a transcriptional repressor in normal breast epithelial cells. Taken together, these findings suggest that CBFA2T3 is a likely candidate for the breast cancer tumor suppressor gene that is the target for the frequent 16q24 LOH in breast neoplasms.
Asunto(s)
Neoplasias de la Mama/genética , Cromosomas Humanos Par 16/genética , Genes Supresores de Tumor , Pérdida de Heterocigocidad , Fosfoproteínas , Proteínas/genética , Proteínas Supresoras de Tumor , División Celular/genética , Regulación Neoplásica de la Expresión Génica , Humanos , Biosíntesis de Proteínas , Proteínas/fisiología , ARN Mensajero/genética , ARN Mensajero/metabolismo , ARN Neoplásico/biosíntesis , ARN Neoplásico/genética , Proteínas Represoras , Células Tumorales CultivadasRESUMEN
The Omega class glutathione transferases (GSTs) have been identified in many organisms, including human, mouse, rat, pig, Caenorhabditis eglands and Drosophila melanogaster. These GSTs have poor activity with common GST substrates, but exhibit novel glutathione-dependent thioltransferase, dehydroascorbate reductase and monomethylarsonate reductase activities, and modulate Ca release by ryanodine receptors. An investigation of the genomic organization of human GSTO1 identified a second actively transcribed member of the Omega class (GSTO1). Both GSTO1 and GSTO2 are composed of six exons and are separated by 7.5 kb on chromosome 10q24.3. A third sequence that appears to be a reverse-transcribed pseudogene (GSTO3p) has been identified on chromosome 3. GSTO2 has 64% amino acid identity with GSTO1 and conserves the cysteine residue at position 32, which is thought to be important in the active site of GSTO1. Expression of GSTO2 mRNA was seen in a range of tissues, including the liver, kidney, skeletal muscle and prostate. The strongest GSTO2 expression was in the testis, which also expresses a larger transcript than other tissues. Characterization of recombinant GSTO2 has been limited by its poor solubility. Two functional polymorphisms of GSTO1 have been identified. One alters a splice junction and causes the deletion of E155 and another results in an A140D substitution. Characterization of these variants revealed that the A140D substitution affects neither heat stability, nor activity towards 1-chloro-2,4-dinitrobenzene or hydroxyethyl disulphide. In contrast, deletion of residue E155 appears to contribute towards both a loss of heat stability and increased enzymatic activity.
Asunto(s)
Glutatión Transferasa/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Mapeo Cromosómico , Cromosomas Humanos Par 10 , Clonación Molecular , ADN Complementario , Exones , Glutatión Transferasa/química , Humanos , Datos de Secuencia Molecular , Seudogenes , ARN Mensajero/genética , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Eliminación de Secuencia , Homología de Secuencia de Aminoácido , Homología de Secuencia de Ácido NucleicoRESUMEN
BACKGROUND: The CBFA2T3 locus located on the human chromosome region 16q24.3 is frequently deleted in breast tumors. CBFA2T3 gene expression levels are aberrant in breast tumor cell lines and the CBFA2T3B isoform is a potential tumor suppressor gene. In the absence of identified mutations to further support a role for this gene in tumorigenesis, we explored whether the CBFA2T3B promoter region is aberrantly methylated and whether this correlates with expression. RESULTS: Aberrant hypo and hypermethylation of the CBFA2T3B promoter was detected in breast tumor cell lines and primary breast tumor samples relative to methylation index interquartile ranges in normal breast counterpart and normal whole blood samples. A statistically significant inverse correlation between aberrant CBFA2T3B promoter methylation and gene expression was established. CONCLUSION: CBFA2T3B is a potential breast tumor suppressor gene affected by aberrant promoter methylation and gene expression. The methylation levels were quantitated using a second-round real-time methylation-specific PCR assay. The detection of both hypo and hypermethylation is a technicality regarding the methylation methodology.
Asunto(s)
Neoplasias de la Mama/genética , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Regiones Promotoras Genéticas/genética , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Proteínas Supresoras de Tumor/genética , Proteínas Supresoras de Tumor/metabolismo , Neoplasias de la Mama/patología , Línea Celular Tumoral , ADN de Neoplasias/química , ADN de Neoplasias/genética , Regulación de la Expresión Génica/genética , Regulación Neoplásica de la Expresión Génica/genética , Humanos , Metilación , Fosfoproteínas/química , Subunidades de Proteína/genética , Proteínas Represoras/química , Análisis de Secuencia de ADN/métodos , Sulfitos/metabolismo , Proteínas Supresoras de Tumor/químicaRESUMEN
Wolfram syndrome (WFS) is a rare, autosomal recessive neurodegenerative disorder. An increased risk of psychiatric disorders and suicide has been reported for heterozygote carriers. In this study we investigated whether mutations in the WFS gene are associated with suicide in the general population. The gene for WFS (WFS1) has recently been mapped to chromosome 4p16.1, and its genomic structure has been characterized. We screened the entire WFS1 ORF in a panel of 100 completed suicides, 60 blood donors not known to have psychiatric illness, and 100 donors with a negative history of depression or suicidal behavior. We did not find evidence of an increased incidence of WFS carriers in the suicide panel and concluded that WFS1 carrier status is not a significant contributor to suicide in the general population. Screening of this highly polymorphic gene resulted in the detection of 33 variants, 13 of which cause amino acid changes. Seven of these changes have not been previously reported and six were unique to our suicide panel.
Asunto(s)
Heterocigoto , Suicidio , Síndrome de Wolfram/genética , Adulto , Alelos , ADN/química , ADN/genética , Análisis Mutacional de ADN , Frecuencia de los Genes , Humanos , Proteínas de la Membrana/genética , Persona de Mediana Edad , Mutación Missense , Mutación Puntual , Polimorfismo de Nucleótido Simple/genética , Polimorfismo Conformacional Retorcido-Simple , Síndrome de Wolfram/psicologíaRESUMEN
Cryptic subtelomeric chromosome anomalies have been recognized as a significant cause of dysmorphology and mental retardation. To determine whether the clinical cytogenetics laboratory should screen routinely for these aberrations, we have tested 250 patients with idiopathic mental retardation/developmental delay, either isolated (53) or associated with dysmorphic features and/or malformations in the absence of a recognizable syndrome (197). All had normal karyotypes at the 550-850 band level. Subtelomeric anomalies were found in 1/53 of the first group (1.9%) and 8/197 of the second group (4.1%). In one patient, two separate anomalies were present: a deletion (not inherited) and a duplication (inherited). It is possible that one of these 10 observed aberrations might represent a rare and previously unreported polymorphism and one a rare cross-hybridization. Our study supports the proposition that cryptic subtelomeric rearrangements are a significant cause of idiopathic mental retardation/developmental delay, but both the diversity of the phenotypes of the positive cases and the wide diversity of their associated chromosome abnormalities emphasize the central problem for the clinical cytogenetics laboratory-that of choosing the most productive patient base for this useful diagnostic test.
Asunto(s)
Aberraciones Cromosómicas , Hibridación Fluorescente in Situ , Discapacidad Intelectual/genética , Telómero , Adolescente , Niño , Preescolar , Deleción Cromosómica , Sondas de ADN , Femenino , Duplicación de Gen , Humanos , Discapacidad Intelectual/etiología , Masculino , Tamizaje Masivo , LinajeRESUMEN
Epilepsy and mental retardation limited to females (EFMR) is a disorder with an X-linked mode of inheritance and an unusual expression pattern. Disorders arising from mutations on the X chromosome are typically characterized by affected males and unaffected carrier females. In contrast, EFMR spares transmitting males and affects only carrier females. Aided by systematic resequencing of 737 X chromosome genes, we identified different protocadherin 19 (PCDH19) gene mutations in seven families with EFMR. Five mutations resulted in the introduction of a premature termination codon. Study of two of these demonstrated nonsense-mediated decay of PCDH19 mRNA. The two missense mutations were predicted to affect adhesiveness of PCDH19 through impaired calcium binding. PCDH19 is expressed in developing brains of human and mouse and is the first member of the cadherin superfamily to be directly implicated in epilepsy or mental retardation.
Asunto(s)
Cadherinas/genética , Cromosomas Humanos X , Codón sin Sentido/genética , Trastornos del Conocimiento/genética , Epilepsia/genética , Impresión Genómica , Mutación Missense/genética , Animales , Encéfalo/crecimiento & desarrollo , Encéfalo/metabolismo , Encéfalo/patología , Estudios de Casos y Controles , Trastornos del Conocimiento/patología , Epilepsia/patología , Femenino , Fibroblastos/citología , Fibroblastos/metabolismo , Regulación del Desarrollo de la Expresión Génica , Genes Ligados a X/genética , Humanos , Hibridación in Situ , Masculino , Discapacidad Intelectual Ligada al Cromosoma X/genética , Discapacidad Intelectual Ligada al Cromosoma X/patología , Ratones/embriología , Linaje , Fenotipo , Protocadherinas , ARN Mensajero/genética , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Piel/citología , Piel/metabolismoRESUMEN
A "new genetics" has emerged driven by knowledge gained at the DNA level. In clinical practice, a practical application of the new genetics is DNA testing, which can be expected to expand with the completion of the Human Genome Project as the functions of new genes are discovered. Genetic DNA testing scenarios include diagnostic DNA testing, prenatal DNA testing, predictive (presymptomatic) DNA testing and screening DNA testing. The challenge for genetic DNA testing and clinical practice will be to define the roles to be played by the general practitioner, the specialist, and other healthcare professionals. From the patients' and families' perspective, the new genetics will best be implemented if a planned approach is adopted in the ordering of DNA tests and the associated counselling and support processes.
Asunto(s)
ADN/genética , Genética Médica/legislación & jurisprudencia , Asesoramiento Genético/normas , Técnicas Genéticas , Pruebas Genéticas/métodos , Pruebas Genéticas/normas , Genética Médica/normas , HumanosRESUMEN
Much is understood about the response of the brain to seizure but little is known in relation to the underlying molecular mechanisms involved. We used microarray technology to investigate the complex genetic response of the brain to generalized seizure. For this investigation a seizure-specific mouse brain cDNA library was generated and spotted onto microarray slides with the aim of increasing the likelihood of identifying novel genes responsive to seizure. Microarray analysis was performed on mouse hippocampus 1 h after generalized seizure pharmacologically induced by pentylenetetrazol (PTZ). Using the custom microarray slides, six genes were identified as being up-regulated in this seizure model and results were validated by real-time PCR. Four of the seizure-responsive genes had previously-reported roles in apoptosis, proliferation or differentiation of neural cells. Two of the genes were novel and in situ hybridization analysis demonstrated heightened mRNA expression in the hippocampus 1 h following generalized convulsive seizure, in a pattern which is typical for other activity-dependant genes expressed in this structure. In addition to being up-regulated postseizure, the genes described in this paper appear to be expressed normally in the adult hippocampus and during development.
Asunto(s)
Proteínas de Unión al ADN/genética , Proteínas del Tejido Nervioso/genética , Convulsiones/genética , Factores de Transcripción/genética , Animales , Secuencia de Bases , Encéfalo/fisiopatología , Cartilla de ADN , Hipocampo/fisiología , Hipocampo/fisiopatología , Hibridación in Situ , Cinética , Masculino , Ratones , Ratones Endogámicos C57BL , Análisis de Secuencia por Matrices de Oligonucleótidos , Reacción en Cadena de la Polimerasa , Valores de Referencia , Proteínas Represoras , Convulsiones/fisiopatologíaRESUMEN
The factor H family of genes has been localised to human chromosome 1q32. This region encodes various proteins involved in complement regulation and is known as the regulators of complement activation (RCA) gene cluster. The factor H genes encode seven known plasma proteins. Using fluorescence in situ hybridisation (FISH), radiation hybrid (RH) mapping and BLAST alignment analysis, we have established that the factor H-related 5 (FHR-5) gene is closely linked to the other factor H gene family members. Analysis of the genomic sequence indicates that the FHR-5 gene is situated between FHR-2 and the non-complement protein factor XIIIb (Fl3B). Like all members of the factor H family. transcription of FHR-5 is in the telomeric direction. Furthermore, the short consensus repeats (SCRs) of FHR-5 are encoded by individual exons and splicing is of type 1. These data allow the generation of a more complete map of the factor H gene family.
Asunto(s)
Proteínas Sanguíneas/genética , Cromosomas Humanos Par 1 , Secuencia de Bases , Proteínas del Sistema Complemento , Humanos , Hibridación Fluorescente in Situ , Datos de Secuencia Molecular , Mapeo de Híbrido por Radiación , Alineación de SecuenciaRESUMEN
A major challenge in understanding complex idiopathic generalized epilepsies has been the characterization of their underlying molecular genetic basis. Here, we report that genetic variation within the GABRD gene, which encodes the GABAA receptor delta subunit, affects GABA current amplitude consistent with a model of polygenic susceptibility to epilepsy in humans. We have found a GABRD Glu177Ala variant which is heterozygously associated with generalized epilepsy with febrile seizures plus. We also report an Arg220His allele in GABRD which is present in the general population. Compared with wild-type receptors, alpha1beta2Sdelta GABAA receptors containing delta Glu177Ala or Arg220His have decreased GABAA receptor current amplitudes. As GABAA receptors mediate neuronal inhibition, the reduced receptor current associated with both variants is likely to be associated with increased neuronal excitability. Since delta subunit-containing receptors localize to extra- or peri-synaptic membranes and are thought to be involved in tonic inhibition, our results suggest that alteration of this process may contribute to the common generalized epilepsies.
Asunto(s)
Sustitución de Aminoácidos/genética , Epilepsia Generalizada/genética , Predisposición Genética a la Enfermedad , Herencia Multifactorial , Mutación Puntual , Receptores de GABA-A/genética , Epilepsia Generalizada/fisiopatología , Femenino , Heterocigoto , Homocigoto , Humanos , Masculino , Linaje , Convulsiones Febriles/genética , Convulsiones Febriles/fisiopatología , Membranas Sinápticas/patologíaRESUMEN
X-linked West syndrome, also called "X-linked infantile spasms" (ISSX), is characterized by early-onset generalized seizures, hypsarrhythmia, and mental retardation. Recently, we have shown that the majority of the X-linked families with infantile spasms carry mutations in the aristaless-related homeobox gene (ARX), which maps to the Xp21.3-p22.1 interval, and that the clinical picture in these patients can vary from mild mental retardation to severe ISSX with additional neurological abnormalities. Here, we report a study of two severely affected female patients with apparently de novo balanced X;autosome translocations, both disrupting the serine-threonine kinase 9 (STK9) gene, which maps distal to ARX in the Xp22.3 region. We show that STK9 is subject to X-inactivation in normal female somatic cells and is functionally absent in the two patients, because of preferential inactivation of the normal X. Disruption of the same gene in two unrelated patients who have identical phenotypes (consisting of early-onset severe infantile spasms, profound global developmental arrest, hypsarrhythmia, and severe mental retardation) strongly suggests that lack of functional STK9 protein causes severe ISSX and that STK9 is a second X-chromosomal locus for this disorder.
Asunto(s)
Enfermedades Genéticas Ligadas al Cromosoma X/genética , Discapacidad Intelectual/genética , Proteínas Serina-Treonina Quinasas/genética , Espasmos Infantiles/genética , Secuencia de Bases , Mapeo Cromosómico , Cromosomas Humanos Par 7 , Discapacidades del Desarrollo/genética , Compensación de Dosificación (Genética) , Femenino , Genes Homeobox , Humanos , Lactante , Datos de Secuencia Molecular , Translocación GenéticaRESUMEN
Loss of heterozygosity (LOH) of chromosome 16q24.3 is a common genetic alteration observed in invasive ductal and lobular breast carcinomas. We constructed a physical map and generated genomic DNA sequence data spanning 2.4 Mb in this region. Detailed in silico and in vitro analyses of the genomic sequence data enabled the identification of 104 genes. It was hypothesized that tumor-suppressor genes would exhibit marked mRNA expression variability in a panel of breast cancer cell lines as a result of downregulation due to mutation or hypermethylation. We examined the mRNA expression profiles of the genes identified at 16q24.3 in normal breast, a normal breast epithelial cell line, and several breast cancer cell lines exhibiting 16q24.3 LOH. Three of the genes, CYBA, Hs.7970, and CBFA2T3, exhibited variability ten times higher than the baseline. The possible role of these genes as tumor suppressors is discussed.
Asunto(s)
Neoplasias de la Mama/genética , Cromosomas Humanos Par 16 , Genes Supresores de Tumor , Pérdida de Heterocigocidad , Femenino , Perfilación de la Expresión Génica , Predisposición Genética a la Enfermedad , Humanos , Mapeo Físico de Cromosoma , Análisis de Secuencia de ADNRESUMEN
Hemopoietic cells, apparently committed to one lineage, can be reprogrammed to display the phenotype of another lineage. The J2E erythroleukemic cell line has on rare occasions developed the features of monocytic cells. Subtractive hybridization was used in an attempt to identify genes that were up-regulated during this erythroid to myeloid transition. We report here on the isolation of hemopoietic lineage switch 5 (Hls5), a gene expressed by the monocytoid variant cells, but not the parental J2E cells. Hls5 is a novel member of the RBCC (Ring finger, B box, coiled-coil) family of genes, which includes Pml, Herf1, Tif-1alpha, and Rfp. Hls5 was expressed in a wide range of adult tissues; however, at different stages during embryogenesis, Hls5 was detected in the branchial arches, spinal cord, dorsal root ganglia, limb buds, and brain. The protein was present in cytoplasmic granules and punctate nuclear bodies. Isolation of the human cDNA and genomic DNA revealed that the gene was located on chromosome 8p21, a region implicated in numerous leukemias and solid tumors. Enforced expression of Hls5 in HeLa cells inhibited cell growth, clonogenicity, and tumorigenicity. It is conceivable that HLS5 is one of the tumor suppressor genes thought to reside at the 8p21 locus.
Asunto(s)
Proteínas Portadoras/genética , Proteínas Portadoras/fisiología , Genes Supresores de Tumor , Células Madre Hematopoyéticas/citología , Secuencia de Aminoácidos , Animales , Apoptosis , Proteínas Reguladoras de la Apoptosis , Secuencia de Bases , Encéfalo/embriología , Química Encefálica , Región Branquial/química , Región Branquial/embriología , Proteínas Portadoras/química , Ciclo Celular , Diferenciación Celular , Línea Celular Tumoral , Núcleo Celular/química , Cromosomas Humanos Par 8 , Gránulos Citoplasmáticos/química , ADN/análisis , ADN Complementario/química , ADN Complementario/aislamiento & purificación , Desarrollo Embrionario y Fetal , Extremidades/embriología , Ganglios Espinales/química , Ganglios Espinales/embriología , Células HeLa , Humanos , Leucemia Eritroblástica Aguda , Ratones , Microscopía Fluorescente , Datos de Secuencia Molecular , Sistemas de Lectura Abierta , Médula Espinal/química , Médula Espinal/embriología , TransfecciónRESUMEN
Fragile sites appear visually as nonstaining gaps on chromosomes that are inducible by specific cell culture conditions. Expansion of CGG/CCG repeats has been shown to be the molecular basis of all five folate-sensitive fragile sites characterized molecularly so far, i.e., FRAXA, FRAXE, FRAXF, FRA11B, and FRA16A. In the present study we have refined the localization of the FRA10A folate-sensitive fragile site by fluorescence in situ hybridization. Sequence analysis of a BAC clone spanning FRA10A identified a single, imperfect, but polymorphic CGG repeat that is part of a CpG island in the 5'UTR of a novel gene named FRA10AC1. The number of CGG repeats varied in the population from 8 to 13. Expansions exceeding 200 repeat units were methylated in all FRA10A fragile site carriers tested. The FRA10AC1 gene consists of 19 exons and is transcribed in the centromeric direction from the FRA10A repeat. The major transcript of approximately 1450 nt is ubiquitously expressed and codes for a highly conserved protein, FRA10AC1, of unknown function. Several splice variants leading to alternative 3' ends were identified (particularly in testis). These give rise to FRA10AC1 proteins with altered COOH-termini. Immunofluorescence analysis of full-length, recombinant EGFP-tagged FRA10AC1 protein showed that it was present exclusively in the nucleoplasm. We show that the expression of FRA10A, in parallel to the other cloned folate-sensitive fragile sites, is caused by an expansion and subsequent methylation of an unstable CGG trinucleotide repeat. Taking advantage of three cSNPs within the FRA10AC1 gene we demonstrate that one allele of the gene is not transcribed in a FRA10A carrier. Our data also suggest that in the heterozygous state FRA10A is likely a benign folate-sensitive fragile site.