Clustered variants in the 5' coding region of TRA2B cause a distinctive neurodevelopmental syndrome.

PURPOSE: Transformer2 proteins (Tra2α and Tra2ß) control splicing patterns in human cells, and no human phenotypes have been associated with germline variants in these genes. The aim of this work was to associate germline variants in the TRA2B gene to a novel neurodevelopmental disorder. METHODS: A total of 12 individuals from 11 unrelated families who harbored predicted loss-of-function monoallelic variants, mostly de novo, were recruited. RNA sequencing and western blot analyses of Tra2ß-1 and Tra2ß-3 isoforms from patient-derived cells were performed. Tra2ß1-GFP, Tra2ß3-GFP and CHEK1 exon 3 plasmids were transfected into HEK-293 cells. RESULTS: All variants clustered in the 5' part of TRA2B, upstream of an alternative translation start site responsible for the expression of the noncanonical Tra2ß-3 isoform. All affected individuals presented intellectual disability and/or developmental delay, frequently associated with infantile spasms, microcephaly, brain anomalies, autism spectrum disorder, feeding difficulties, and short stature. Experimental studies showed that these variants decreased the expression of the canonical Tra2ß-1 isoform, whereas they increased the expression of the Tra2ß-3 isoform, which is shorter and lacks the N-terminal RS1 domain. Increased expression of Tra2ß-3-GFP were shown to interfere with the incorporation of CHEK1 exon 3 into its mature transcript, normally incorporated by Tra2ß-1. CONCLUSION: Predicted loss-of-function variants clustered in the 5' portion of TRA2B cause a new neurodevelopmental syndrome through an apparently dominant negative disease mechanism involving the use of an alternative translation start site and the overexpression of a shorter, repressive Tra2ß protein.

Tissue mosaicism, FMR1 expression and intellectual functioning in males with fragile X syndrome.

Fragile X syndrome (FXS) is caused by hypermethylation of the FMR1 promoter due to the full mutation expansion (full mutation [FM]: CGG ≥ 200 repeats) and silencing of FMR1. Assessment of mosaicism for active-unmethylated alleles has prognostic utility. This study examined relationships between FMR1 methylation in different tissues with FMR1 messenger ribonucleic acid (mRNA) and intellectual functioning in 87 males with FXS (1.89-43.17 years of age). Methylation sensitive Southern blot (mSB) and Methylation Specific-Quantitative Melt Aanalysis (MS-QMA) were used to examine FMR1 methylation. FMR1 mRNA levels in blood showed strong relationships with FMR1 methylation assessed using MS-QMA in blood (n = 68; R2  = 0.597; p = 1.4 × 10-10 ) and buccal epithelial cells (BEC) (n = 62; R2  = 0.24; p = 0.003), with these measures also showing relationships with intellectual functioning scores (p < 0.01). However, these relationships were not as strong for mSB, with ~40% of males with only FM alleles that were 100% methylated and non-mosaic by mSB, showing methylation mosaicism by MS-QMA. This was confirmed through presence of detectable levels of FMR1 mRNA in blood. In summary, FMR1 methylation levels in blood and BEC examined by MS-QMA were significantly associated with FMR1 mRNA levels and intellectual functioning in males with FXS. These relationships were not as strong for mSB, which underestimated prevalence of mosaicism.

Agreement between parents' and clinical researchers' ratings of behavioral problems in children with fragile X syndrome and chromosome 15 imprinting disorders.

BACKGROUND: Despite the increasing number of clinical trials involving children with neurodevelopmental disorders, appropriate and objective outcome measures for behavioral symptoms are still required. AIM: This study assessed the agreement between parents' and clinical researchers' ratings of behavioral problem severity in children with fragile X syndrome (FXS) and chromosome 15 imprinting disorders. METHODS AND PROCEDURES: The cohort comprised 123 children (64% males), aged 3-17 years, with FXS (n = 79), Prader-Willi (PWS; n = 19), Angelman (AS; n = 15), and Chromosome 15q duplication (n = 10) syndromes. Specific items from the Autism Diagnostic Observation Schedule-Second Edition and Aberrant Behavior Checklist-Community Edition mapping to corresponding behavioral domains were selected ad-hoc, to assess behavioral problems. OUTCOMES AND RESULTS: Inter-rater agreement for the cohort was slight for self-injury (Intraclass Correlation Coefficient (ICC) = 0.12), fair for tantrums/aggression (0.24) and mannerisms/stereotypies (0.25), and moderate for hyperactivity (0.48). When stratified by diagnosis, ICC ranged from poor (0; self-injury, AS and PWS) to substantial (0.48; hyperactivity, females with FXS). CONCLUSIONS AND IMPLICATIONS: The high level of inter-rater disagreement across most domains suggests that parents' and researchers' assessments led to discrepant appraisal of behavioral problem severity. These findings have implications for treatment targets and outcome measure selection in clinical trials, supporting a multi-informant approach.

Feasibility of Screening for Chromosome 15 Imprinting Disorders in 16 579 Newborns by Using a Novel Genomic Workflow.

Importance: Newborn screening for Angelman syndrome (AS), Prader-Willi syndrome (PWS), and chromosome 15 duplication syndrome (Dup15q) may lead to benefit from early diagnosis and treatment. Objective: To examine the feasibility of newborn screening for these chromosome 15 imprinting disorders at population scale. Design, Setting, and Participants: In this diagnostic study, the validation data set for the first-tier SNRPN test, called methylation-specific quantitative melt analysis (MS-QMA), included 109 PWS, 48 AS, 9 Dup15q, and 1190 population control newborn blood spots (NBS) and peripheral tissue samples from participants recruited from January 2000 to December 2016. The test data set included NBS samples from 16 579 infants born in 2011. Infants with an NBS identified as positive for PWS, AS, or Dup15q by the first-tier test were referred for droplet digital polymerase chain reaction, real-time polymerase chain reaction, and low-coverage whole-genome sequencing for confirmatory testing. Data analyses were conducted between February 12, 2015, and August 15, 2020. Results: In the validation data set, the median age for the 77 patients with PWS was 3.00 years (IQR, 0.01-44.50 years); for the 46 patients with AS, 2.76 years (IQR, 0.028 to 49.00 years); and for the 9 patients with Dup15q, 4.00 years (IQR, 1.00 to 28.00 years). Thirty-eight patients (51.4%) in the PWS group, 20 patients (45.5%) in the AS group, and 6 patients (66.7%) in the Dup15q group who had sex reported were male. The validation data set showed MS-QMA sensitivity of 99.0% for PWS, 93.8% for AS, and 77.8% for Dup15q; specificity of 100% for PWS, AS, and Dup15q; positive predictive and negative predictive values of 100% for PWS and AS; and a positive predictive value of 87.5% and negative predictive value of 100% for Dup15q. In the test data set of NBS samples from 16 579 infants, 92 had a positive test result using a methylation ratio cut-off of 3 standard deviations from the mean. Of these patients, 2 were confirmed to have PWS; 2, AS; and 1, maternal Dup15q. With the use of more conservative PWS- and AS-specific thresholds for positive calls from the validation data set, 9 positive NBS results were identified by MS-QMA in this cohort. The 2 PWS and 2 AS calls were confirmed by second-tier testing, but the 1 Dup15q case was not confirmed. Together, these results provided prevalence estimates of 1 in 8290 for both AS and PWS and 1 in 16 579 for maternal Dup15q, with positive predictive values for first-tier testing at 67.0% for AS, 33.0% for PWS, and 44.0% for combined detection of chromosome 15 imprinting disorders for the validation data set. Conclusions and Relevance: The findings of this diagnostic study suggest that it is feasible to screen for all chromosome 15 imprinting disorders using SNRPN methylation analysis, with 5 individuals identified with these disorders out of 16 579 infants screened.

FMR1 mRNA from full mutation alleles is associated with ABC-CFX scores in males with fragile X syndrome.

Fragile X syndrome (FXS) is caused by a hypermethylated full mutation (FM) expansion with ≥ 200 CGG repeats, and a decrease in FMR1 mRNA and its protein. However, incomplete silencing from FM alleles has been associated with more severe autism features in FXS males. This study compared scores on the Aberrant Behavior Checklist-Community-FXS version (ABC-CFX) in 62 males affected with FXS (3 to 32 years) stratified based on presence or absence of mosaicism and/or FMR1 mRNA silencing. Associations between ABC-CFX subscales and FMR1 mRNA levels, assessed using real-time PCR relative standard curve method, were also examined. The FXS group mosaic for premutation (PM: 55-199 CGGs) and FM alleles had lower irritability (p = 0.014) and inappropriate speech (p < 0.001) scores compared to males with only FM alleles and complete loss of FMR1 mRNA. The PM/FM mosaic group also showed lower inappropriate speech scores compared to the incomplete silencing (p = 0.002) group. Increased FMR1 mRNA levels were associated with greater irritability (p < 0.001), and lower health-related quality of life scores (p = 0.004), but only in the incomplete silencing FM-only group. The findings suggest that stratification based on CGG sizing and FMR1 mRNA levels may be warranted in future research and clinical trials utilising ABC-CFX subscales as outcome measures.

Incomplete silencing of full mutation alleles in males with fragile X syndrome is associated with autistic features.

Background: Fragile X syndrome (FXS) is a common monogenic cause of intellectual disability with autism features. While it is caused by loss of the FMR1 product (FMRP), mosaicism for active and inactive FMR1 alleles, including alleles termed premutation (PM: 55-199 CGGs), is not uncommon. Importantly, both PM and active full mutation (FM: ≥ 200 CGGs) alleles often express elevated levels of mRNA that are thought to be toxic. This study determined if complete FMR1 mRNA silencing from FM alleles and/or levels of FMR1 mRNA (if present) in blood are associated with intellectual functioning and autism features in FXS. Methods: The study cohort included 98 participants (70.4% male) with FXS (FM-only and PM/FM mosaic) aged 1-43 years. A control group of 14 females were used to establish control FMR1 mRNA reference range. Intellectual functioning and autism features were assessed using the Mullen Scales of Early Learning or an age-appropriate Wechsler Scale and the Autism Diagnostic Observation Schedule-2nd Edition (ADOS-2), respectively. FMR1 mRNA was analysed in venous blood collected at the time of assessments, using the real-time PCR relative standard curve method. Results: Females with FXS had significantly higher levels of FMR1 mRNA (p < 0.001) than males. FMR1 mRNA levels were positively associated with age (p < 0.001), but not with intellectual functioning and autistic features in females. FM-only males (aged < 19 years) expressing FM FMR1 mRNA had significantly higher ADOS calibrated severity scores compared to FM-only males with completely silenced FMR1 (p = 0.011). However, there were no significant differences between these subgroups on intellectual functioning. In contrast, decreased levels of FMR1 mRNA were associated with decreased intellectual functioning in FXS males (p = 0.029), but not autism features, when combined with the PM/FM mosaic group. Conclusion: Incomplete silencing of toxic FM RNA may be associated with autistic features, but not intellectual functioning in FXS males. While decreased levels of mRNA may be more predictive of intellectual functioning than autism features. If confirmed in future studies, these findings may have implications for patient stratification, outcome measure development, and design of clinical and pre-clinical trials in FXS.

[Microarrays in 236 patients with neurodevelopmental disorders and congenital abnormalities]. / Microarreglos cromosómicos en 236 pacientes chilenos con trastornos del neurodesarrollo y anomalías congénitas.

BACKGROUND: In 20% of neurodevelopmental disorders (NDD) and congenital abnormalities (CA) the cause would be a genomic imbalance detectable only by chromosomal microarrays (CMA). AIM: To analyze the results of CMA performed at the INTA Laboratory of Molecular Cytogenetics, during a period of four years in patients with NDD or CA. MATERIAL AND METHODS: Retrospective study that included all CMA reports of Chilean patients. Age, sex, clinical diagnosis and origin were analyzed, as well as the characteristics of the finding. The percentage of cases diagnosed by CMA was calculated considering all patients with pathogenic (PV) or probably pathogenic variants (VLP). Finally, we studied the association between patients' characteristics and a positive CMA outcome. RESULTS: A total of 236 reports were analyzed. The median age was 5.41 (range 2.25-9.33) years, and 59% were men. Ninety chromosomal imbalances were found, which corresponded mainly to deletions (53.3%), with a median size of 1.662 (range 0.553-6.673) Megabases. The diagnostic rate of CMA in Chilean patients from all over the country was 19.2%. There was a close relationship between the patient's sex and the detection of VLP/VP (p = 0.034). CONCLUSIONS: Our diagnostic rate and the association between female sex and a higher percentage of diagnosed cases are concordant with other international studies. Therefore, CMA is a valid diagnostic tool in the Chilean population.

Microarreglos cromosómicos en 236 pacientes chilenos con trastornos del neurodesarrollo y anomalías congénitas / Microarrays in 236 patients with neurodevelopmental disorders and congenital abnormalities

Background: In 20% of neurodevelopmental disorders (NDD) and congenital abnormalities (CA) the cause would be a genomic imbalance detectable only by chromosomal microarrays (CMA). Aim: To analyze the results of CMA performed at the INTA Laboratory of Molecular Cytogenetics, during a period of four years in patients with NDD or CA. Material and Methods: Retrospective study that included all CMA reports of Chilean patients. Age, sex, clinical diagnosis and origin were analyzed, as well as the characteristics of the finding. The percentage of cases diagnosed by CMA was calculated considering all patients with pathogenic (PV) or probably pathogenic variants (VLP). Finally, we studied the association between patients' characteristics and a positive CMA outcome. Results: A total of 236 reports were analyzed. The median age was 5.41 (range 2.25-9.33) years, and 59% were men. Ninety chromosomal imbalances were found, which corresponded mainly to deletions (53.3%), with a median size of 1.662 (range 0.553-6.673) Megabases. The diagnostic rate of CMA in Chilean patients from all over the country was 19.2%. There was a close relationship between the patient's sex and the detection of VLP/VP (p = 0.034). Conclusions: Our diagnostic rate and the association between female sex and a higher percentage of diagnosed cases are concordant with other international studies. Therefore, CMA is a valid diagnostic tool in the Chilean population.

Distal 7q11.23 Duplication, an Emerging Microduplication Syndrome: A Case Report and Further Characterisation.

Chromosome 7q11.23 duplication syndrome is a well-recognised syndrome which involves the duplication of the same genes located in the Williams-Beuren critical region. However, in 2010, 4 patients were reported with a microduplication only in the HIP1 and YWHAG genes. We refer to this as a distal 7q11.23 duplication (dup7q11.23D). Here, we report the fifth de novo patient with dup7q11.23D, whose symptoms may be explained by YWHAG overexpression as was demonstrated recently in mice and obese patients. Finally, further studies will be necessary to delineate this emerging microduplication syndrome.

FMR1 gene mutations in patients with fragile X syndrome and obligate carriers: 30 years of experience in Chile.

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability (ID) and co-morbid autism. It is caused by an amplification of the CGG repeat (>200), which is known as the full mutation, within the 5'UTR of the FMR1 gene. Expansions between 55-200 CGG repeats are termed premutation and are associated with a greater risk for fragile X-associated tremor/ataxia syndrome and fragile X-associated premature ovarian insufficiency. Intermediate alleles, also called the grey zone, include approximately 45-54 repeats and are considered borderline. Individuals with less than 45 repeats have a normal FMR1 gene. We report the occurrence of CGG expansions of the FMR1 gene in Chile among patients with ID and families with a known history of FXS. Here, we present a retrospective review conducted on 2321 cases (2202 probands and 119 relatives) referred for FXS diagnosis and cascade screening at the Institute of Nutrition and Food Technology (INTA), University of Chile. Samples were analysed using traditional cytogenetic methods and/or PCR. Southern blot was used to confirm the diagnosis. Overall frequency of FMR1 expansions observed among probands was 194 (8·8%), the average age of diagnosis was 8·8 ± 5·4 years. Of 119 family members studied, 72 (60%) were diagnosed with a CGG expansion. Our results indicated that the prevalence of CGG expansions of the FMR1 gene among probands is relatively higher than other populations. The average age of diagnosis is also higher than reference values. PCR and Southern blot represent a reliable molecular technique in the diagnosis of FXS.

Comparison of two subtelomeric assays for the screening of chromosomal rearrangements: analysis of 383 patients, literature review and further recommendations.

Intellectual disability (ID) and global development delay (GDD) are caused by genetic factors such as subtelomeric rearrangements (SR) in 25 % of patients. There are several assays currently available to detect SR, but subtelomeric fluorescence in situ hybridisation (Subt-FISH) and subtelomeric multiplex ligation-dependent probe amplification (Subt-MLPA) have been the most frequently used. However, the diagnostic yield of each technique has not been compared. We reviewed the results of SR screening over a ten-year period in Chilean patients with ID/GDD using Subt-FISH and/or Subt-MLPA, compared the diagnostic yield of both tools and reviewed the corresponding literature. A total of 383 cases were included in this study, of which 53.8 % were males. The overall diagnostic yield was 8.9 % between both methods, but Subt-MLPA showed a higher performance than Subt-FISH (p = 0.002). A total of 4,181 patients with ID/GDD have been studied worldwide with Subt-MLPA and other subtelomeric assays, and 244 (5.84 %) had a pathogenic SR. It is estimated that Subt-MLPA may detect 92.6 % of the total cases with SR. The capacity of detecting tandem duplication and other critical regions, as well as the use of two MLPA kits, may explain the higher performance of this tool over Subt-FISH. Therefore, we recommend the use of this subtelomeric method as a cost-effective way to study ID/GDD patients.

Identification of Males with Cryptic Fragile X Alleles by Methylation-Specific Quantitative Melt Analysis.

BACKGROUND: FMR1 full mutations (FMs) (CGG expansion >200) in males mosaic for a normal (<45 CGG) or gray-zone (GZ) (45-54 CGG) allele can be missed with the standard 2-step fragile X syndrome (FXS) testing protocols, largely because the first-line PCR tests showing a normal or GZ allele are not reflexed to the second-line test that can detect FM. METHODS: We used methylation-specific quantitative melt analysis (MS-QMA) to determine the prevalence of cryptic FM alleles in 2 independent cohorts of male patients (994 from Chile and 2392 from Australia) referred for FXS testing from 2006 to 2013. All MS-QMA-positive cases were retested with commercial triplet primed PCR, methylation-sensitive Southern blot, and a methylation-specific EpiTYPER-based test. RESULTS: All 38 FMs detected with the standard 2-step protocol were detected with MS-QMA. However, MS-QMA identified methylation mosaicism in an additional 15% and 11% of patients in the Chilean and Australian cohorts, respectively, suggesting the presence of a cryptic FM. Of these additional patients, 57% were confirmed to carry cryptic expanded alleles in blood, buccal mucosa, or saliva samples. Further confirmation was provided by identifying premutation (CGG 55-199) alleles in mothers of probands with methylation-sensitive Southern blot. Neurocognitive assessments showed that low-level mosaicism for cryptic FM alleles was associated with cognitive impairment or autism. CONCLUSIONS: A substantial number of mosaic FM males who have cognitive impairment or autism are not diagnosed with the currently recommended 2-step testing protocol and can be identified with MS-QMA as a first-line test.

Experiencia en el diagnóstico, pesquisa en cascada y manejo multidisciplinario de pacientes con síndrome X frágil / Experience in diagnosis, cascade screening and multidisciplinary management of patients with fragile X syndrome

Resumen. El Síndrome X Frágil (SXF) constituye la causa más frecuente de retraso mental hereditario y autismo. Los individuos con mutación completa (MC) presentan alteraciones clínicas que incluyen: déficit cognitivo y atencional, hiperactividad, autismo y problemas emocionales. Los portadores de premutación (PM) pueden afectarse del síndrome de temblor y ataxia asociado a X frágil (FXTAS); el 30 por ciento de las mujeres con PM presentan insuficiencia ovárica prematura(FXPOI). Cuando un individuo presenta una MC es frecuente encontrar otros familiares afectados. El fenotipo al nacer no es evidente, se sugiere que debe hacerse el diagnóstico entre los35-37 meses, sin embargo, la edad de diagnóstico en Chile es en promedio de 8 +/- 5.8 años. El centro de diagnóstico, tratamiento y seguimiento de pacientes con síndrome X frágil (CDTSXF)es un centro multidisciplinario, que incluye diagnósticos moleculares, genetistas médicos, asesoramiento genético, neurólogos, terapeutas ocupacionales, fonoaudiólogo, evaluaciones nutricionales y psicológicas para las familias afectadas. Desde el año 2010 hemos asistido a 28familias y detectado un número significativo de afectados debido a la detección en cascada. Se ha diagnosticado a 63 probandos, 57 MC y ocho mosaicos de MC/PM. Entre las madres portadoras 37 son PM y dos presentaron una MC. En 9/28 familias había un adulto mayor con FXTAS, diez familias presentaron mujeres con FXPOI. 41/63 probandos han participado denle el protocolo multidisciplinario del CDTSXF. Los resultados de este enfoque multidisciplinario nos motiva a seguir trabajando en mejorar el comportamiento y desarrollo cognitivo de los pacientes y atender las principales necesidades de las familias afectadas.

Fragile X Syndrome (FXS) is the most common inherited form of mental retardation and a leading known cause of autism. Individuals with a full mutation (FM) present disabilities including: cognitive and attention deficit, hyperactivity, autism, and other emotional problems. Carriers of a premutation (PM) may be affected by fragile X associated tremor/ataxia syndrome (FXTAS) and primary ovarian insufficiency (FXPOI) in 30 percent of PM women. Therefore, multigenerational family involvement is commonly found when a proband is diagnosed with a FXS mutation. FXS has no obvious phenotype at birth, it is suggested that the diagnosis should be made at 35-37 months; the age of diagnosis in Chile is on average 8+/-5.8 yo. The center for diagnosis, treatment and monitoring of patients with fragile X syndrome (CDTTRABAJOMFXS), is a multidisciplinary center that includes molecular testing, medical geneticists, genetic counseling, neurologists, occupational therapists, physical therapists, and nutritional and psychological interventions to families with an FM proband. Since 2010, we have assisted 28 families with a total of 63 diagnosed probands using specific PCR and Southern blot tests. Among them, 57 had a FM and eight had a mosaic FM/PM. Among the mothers 37 are PM carriers and two presented a FM. An older adult with FXTAS was present in 9/28 families; ten families presented women with FXPOI. A significant number of affected family members have been detected through cascade screening. Among the probands 41 of 63 have received some of the multidisciplinary diagnostic and interventions. The results of this multidisciplinary work allow us to put forward more effort towards improving behavior and cognitive development of patients as well as trying to solve families’ main needs.

[Cytogenetic and molecular profile of genetic diseases in Puerto Montt main hospital]. / Caracterización citogenético-molecular de enfermedades genéticas en el Hospital Base de Puerto Montt.

BACKGROUND: Chromosome aberrations (CA) are the main etiology of multiple congenital malformations, recurrent abortions and intellectual disability (ID) specifically of moderate and severe degree. They account for 0.3 to 1% of newborns (NB) and 6 of 10,000 NB have chromosome imbalances with submicroscopic deletions or duplications smaller than 10 MB that are overlooked by conventional cytogenetic studies. AIM: To report the results of cytogenetic and molecular studies performed in patients with a congenital malformation disease or ID with or without dysmorphic features, attended in a regional hospital. PATIENTS AND METHODS: One hundred and eighty patients, 27 with a clinical diagnosis of Down syndrome, derived for the suspicion of a genetic disease, were studied. A karyogram was performed in all of them and in 30 cases additional molecular studies, such as fluorescence in situ hybridization (FISH) or polymerase chain reaction (PCR) were carried out. RESULTS: Among the 153 patients without Down syndrome, 20 (13%) had a genetic abnormality responsible for the altered phenotype. Sixteen had a chromosome aberration (structural and numerical aberrations in 75 and 25% respectively) and four had genetic molecular alterations. Additional studies were performed to confirm or better characterize the chromosome aberration in 13 of the 30 patients in whom these were requested. CONCLUSIONS: Chromosome and specific genetic molecular studies in selected cases help to characterize patients with genetic diseases. The collaboration between academic and health care facilities is crucial.

Caracterización citogenético-molecular de enfermedades genéticas en el Hospital Base de Puerto Montt / Cytogenetic and molecular profile of genetic diseases in Puerto Montt main hospital

Background: Chromosome aberrations (CA) are the main etiology of múltiple congenital malformations, recurrent abortions and intellectual disability (ID) specifically of modérate and severe degree. They accountfor 0.3 to 1 percent of newborns (NB) and 6 of 10,000 NB have chromosome imbalances with submicroscopic deletions or duplications smaller than 10 MB that are overlooked by conventional cytogenetic studies. Aim: To report the results of cytogenetic and molecular studies performed in patients with a congenital malformation disease or ID with or without dysmorphic features, attended in a regional hospital. Patients and Methods: One hundred and eighty patients, 27 with a clinical diagnosis ofDown syndrome, derivedfor the sus-picion of a genetic disease, were studied. A karyogram was performed in all ofthem and in 30 cases additional molecular studies, such as fluorescence in situ hybridization (FISH) orpolymerase chain reaction (PCR) were carried out. Results: Amongthe 153 patients without Down syndrome, 20 (13 percent) had a genetic abnormality responsible for the altered phenotype. Sixteen had a chromosome aberration (structural and numerical aberrations in 75 and 25 percent respectively) andfour had genetic molecular alterations. Additional studies were performed to confirm or better characterize the chromosome aberration in 13 ofthe 30 patients in whom these were requested. Conclusions: Chromosome and specific genetic molecular studies in selected cases help to characterize patients with genetic diseases. The collaboration between academic and health care facilities is crucial.

Diagnóstico citogenético-molecular del síndrome Xq frágil / Diagnostic testing in fragile X syndrome

El síndrome Xq frágil (SXF) es una causa frecuente de retraso mental (RM); se estima que uno de cada 4.000 varones y una década 6.000 mujeres lo presentan. Clínicamente los individuos afectados se caracterizan por presentar déficit intelectual y cognitivo, déficit de lenguaje, macroorquidismo, fascie alargada y orejas prominentes, entre otras dismorfias faciales. A nivel molecular es posible distinguir fundamentalmente dos tipos de alelos mutados: premutacion y mutación completa, las cuales corresponden a amplificación del trinucleótido CGG localizado en el primer exón del gen FMR1; las premutaciones presentan entre 52 y 200 repetidos y las mutaciones completas sobre 200 CGG, con hipermetilación de la región promotora del gen FMR1 e inhibición de la expresión de la proteína FMRP, causante del RM y dismorfias características de este síndrome. Desde que se identifico la mutación en 1991, la pesquisa de pacientes afectados se inicia por el examen clínico y luego el análisis citogenetico clásico y el test de screening basado en PCR para individuos varones y análisis molecular directo del gen FMR 1 por Southern Blot con la sonda Stb 12.3 para pacientes mujeres; los varones que presentan un PCR alterado deben ser confirmados por Southern Blot. El PCR debe ser usado como método de screening solo en varones con RM, sin historia familiar; es un sensible, rápido, de bajo costo y permite determinar el numero de repetidos CGG. Proponemos el uso conjunto de estos métodos para optimizar el estudio molecular directo del gen FMR1 y establecer un protocolo mas eficiente en la pesquisa de afectados, el estudio de familiares a riesgo y el consejo genético adecuado.

Signals from damaged but not undamaged skeletal muscle induce myogenic differentiation of rat bone-marrow-derived mesenchymal stem cells.

The regenerative capacity of skeletal muscle has been usually attributed to resident satellite cells, which, upon activation by local or distant stimuli, initiate a myogenic differentiation program. Although recent studies have revealed that bone-marrow-derived progenitor cells may also participate in regenerative myogenesis, the signals and mechanisms involved in this process have not been elucidated. This study was designed to investigate whether signals from injured rat skeletal muscle were competent to induce a program of myogenic differentiation in expanded cultures of rat bone-marrow-derived mesenchymal stem cells (MSC). We observed that the incubation of MSC with a conditioned medium prepared from chemically damaged but not undamaged muscle resulted in a time-dependent change from fibroblast-like into elongated multinucleated cells, a transient increase in the number of MyoD positive cells, and the subsequent onset of myogenin, alpha-actinin, and myosin heavy chain expression. These results show that damaged rat skeletal muscle is endowed with the capacity to induce myogenic differentiation of bone-marrow-derived mesenchymal progenitors.

[Frequency of C677T polymorphism of 5, 10-methylenetetrahydrofolate reductase (MTHFR) in Chilean mothers of spina bifida cases and controls ]. / Frecuencia del polimorfismo C677T de la 5, 10-metilentetrahidrofolato reductasa (MTHFR) en mujeres chilenas madres de afectados con espina bífida y en controles normales.

BACKGROUND: Several population studies have shown that patients with neural tube defects (NTD), have a higher frequency of a genetic mutation related with thermolability of the enzyme 5,10-metylentetrahydrofolate reductase (MTHFR). There are regional and ethnic variations in the genotypic or allelic frequency of this mutation and its possible relationship with NTD and others congenital anomalies. AIM: To estimate the frequency of the C677T polymorphism of MTHFR in control women and mothers of spina bifida cases. PATIENTS AND METHODS: We analyzed 58 blood samples from mothers who had a child diagnosed with spina bifida. A group of 184 healthy mothers matched by age and with no NTD offspring served as controls. We determined the C677T polymorphism on the MTHFR gene by means of PCR and the analysis of the digestion pattern of HinfI restriction enzyme. RESULTS: The genotypic frequencies showed concordance with Hardy-Weinberg equilibrium, in controls (p = 0.35), and in mothers of the cases (p = 0.95). The odds ratio to the TT genotype compared with the CC genotype (reference category) was estimated as 1.54 (IC 95%: 0.66-3.61), while the odds ratio for the TC genotype compared with CC genotype was 1.06 (IC 95%: 0.48-2.33). CONCLUSION: No differences in the C677T polymorphism of the MTHFR were observed between mothers who had a child diagnosed with spina bifida and control mothers.