Clinical implication of FMR1 intermediate alleles in a Spanish population.

FMR1 premutation carriers (55-200 CGGs) are at risk of developing Fragile X-associated primary ovarian insufficiency as well as Fragile X-associated tremor/ataxia syndrome. FMR1 premutation alleles are also associated with a variety of disorders, including psychiatric, developmental, and neurological problems. However, there is a major concern regarding clinical implications of smaller CGG expansions known as intermediate alleles (IA) or gray zone alleles (45-54 CGG). Although several studies have hypothesized that IA may be involved in the etiology of FMR1 premutation associated phenotypes, this association still remains unclear. The aim of this study was to provide new data on the clinical implications of IA. We reviewed a total of 17 011 individuals: 1142 with primary ovarian insufficiency, 478 with movement disorders, 14 006 with neurodevelopmental disorders and 1385 controls. Similar IA frequencies were detected in all the cases and controls (cases 1.20% vs controls 1.39%, P = .427). When comparing the allelic frequencies of IA ≥ 50CGGs, a greater, albeit not statistically significant, number of alleles were detected in all the cohorts of patients. Therefore, IA below 50 CGGs should not be considered as risk factors for FMR1 premutation-associated phenotypes, at least in our population. However, the clinical implication of IA ≥ 50CGGs remains to be further elucidated.

The MECP2 variant c.925C>T (p.Arg309Trp) causes intellectual disability in both males and females without classic features of Rett syndrome.

Missense MECP2 variants can have various phenotypic effects ranging from a normal phenotype to typical Rett syndrome (RTT). In females, the phenotype can also be influenced by the X-inactivation pattern. In this study, we present detailed clinical descriptions of six patients with a rare base-pair substitution affecting Arg309 at the C-terminal end of the transcriptional repression domain (TRD). All patients have intellectual disability and present with some RTT features, but they do not fulfill the clinical criteria for typical or atypical RTT. Most of the patients also have mild facial dysmorphism. Intriguingly, the mother of an affected male patient is an asymptomatic carrier of this variant. It is therefore likely that the p.(Arg309Trp) variation does not necessarily lead to male lethality, and it results in a wide range of clinical features in females, probably influenced by different X-inactivation patterns in target tissues.

BRCA1 5272-1G>A and BRCA2 5374delTATG are founder mutations of high relevance for genetic counselling in breast/ovarian cancer families of Spanish origin.

The distribution of BRCA1 and BRCA2 germ line mutations in breast/ovarian cancer families varies among different populations, which typically present a wide spectrum of unique mutations. Splicing mutation 5272-1G>A of BRCA1 and frameshift mutation 5374delTATG of BRCA2 are highly prevalent mutations in Castilla-León (Spain), accounting for 18.4% and 13.6% of BRCA1 and BRCA2 positive families, respectively. To test the presence of founder effects, 9 Spanish 5272-1G>A and 13 5374delTATG families were genotyped with polymorphic markers linked to BRCA1 or BRCA2. All the 5272-1G>A families shared a common haplotype in eight markers (1.1 Mb region) and the mutation age was estimated in 15 generations (approximately 380 years). A conserved haplotype associated to 5374delTATG was observed in four markers (0.82 Mb). The mutation occurred approximately 48 generations ago (approximately 1200 years). Each mutation likely arose from a common ancestor that could be traced to a small area of Castilla-León and expanded to other Spanish regions. They can have a significant impact on the clinical management of asymptomatic carriers as well as on the genetic screening strategy to be followed in populations with Spanish ancestries.

X-chromosome tiling path array detection of copy number variants in patients with chromosome X-linked mental retardation.

BACKGROUND: Aproximately 5-10% of cases of mental retardation in males are due to copy number variations (CNV) on the X chromosome. Novel technologies, such as array comparative genomic hybridization (aCGH), may help to uncover cryptic rearrangements in X-linked mental retardation (XLMR) patients. We have constructed an X-chromosome tiling path array using bacterial artificial chromosomes (BACs) and validated it using samples with cytogenetically defined copy number changes. We have studied 54 patients with idiopathic mental retardation and 20 controls subjects. RESULTS: Known genomic aberrations were reliably detected on the array and eight novel submicroscopic imbalances, likely causative for the mental retardation (MR) phenotype, were detected. Putatively pathogenic rearrangements included three deletions and five duplications (ranging between 82 kb to one Mb), all but two affecting genes previously known to be responsible for XLMR. Additionally, we describe different CNV regions with significant different frequencies in XLMR and control subjects (44% vs. 20%). CONCLUSION: This tiling path array of the human X chromosome has proven successful for the detection and characterization of known rearrangements and novel CNVs in XLMR patients.

Screening for MECP2 mutations in Spanish patients with an unexplained mental retardation.

Rett syndrome (RTT) is an X-linked progressive encephalopathy. Mutations in the MECP2 (methyl-CpG-binding protein) gene have been found to cause RTT. In the past few years, the role of MECP2 mutations in patients with mental disorders other than RTT has been studied, finding that mutations in MECP2 also contribute to non-syndromic entities. More recently, it has been demonstrated that RTT shares clinical features with those of Angelman syndrome, another neurodevelopmental disorder. These observations must be confirmed in a large series, to better understand the criteria needed for justifying a molecular test. Consequently, we have searched for MECP2 mutations in 294 patients (43 Angelman and Prader-Willi like included) with mental retardation (MR) of unknown aetiology. We found six polymorphisms (three novel, three previously reported) in 10 patients, one novel unclassified silent change (p.V222V) in a man, and one causative mutation in a girl with MR. Once this case was clinically reviewed, the girl presented symptoms of atypical RTT. The mutation (p.Y141C) lies within the methyl-binding domain, and has only been reported once in another atypical RTT. Our results show that the MECP2 mutations account for a low frequency (1/416 chromosomes = 0.24%) among mentally retarded individuals, which imply that it is necessary to perform an exhaustive clinical examination of patients before determining whether analysis of MECP2 is required or not.

Retraso mental de origen genético. Presentación de la Red GIRMOGEN / Genetic mental retardation. Presentation of the girmogen network

Introducción. El retraso mental es la discapacidad másfrecuente y se pone en evidencia desde la infancia. La OrganizaciónMundial de la Salud (OMS) estima que afecta aproximadamenteal 3% de la población en los países industrializados. Entrelas causas que originan el retraso mental, parece que un 30% sonde origen genético, aunque en los últimos años los avances engenética molecular sobre nuevas mutaciones y nuevos genes responsablesdel retraso mental se suceden con increíble rapidez. Poresta razón, hace tres años un grupo de profesionales clínicos einvestigadores, que trabajábamos mayoritariamente en España enel síndrome X frágil (el más prevalente de los hereditarios de retrasomental), propusimos la creación de GIRMOGEN (Grupo de Investigaciónde Retraso Mental de Origen Genético). La mayoría denosotros habíamos constatado que muchos de los casos clínicosque llegaban a nuestras manos quedaban sin diagnóstico, y desconocíamosla prevalencia exacta de esta discapacidad en España.Desarrollo. GIRMOGEN fue financiada por el Instituto de SaludCarlos III. Está formada por ocho grupos; un noveno grupo se encargade la coordinación. Sus miembros están todos implicados en estudios clínicos o de investigación sobre el retraso mental de origengenético, y pertenecen a 15 hospitales y a cinco universidadesde un total de 11 comunidades autónomas del Estado español. Entresus objetivos se encuentran: juntar todos los datos de pacientesy familias en una base común para estudios epidemiológicos y deprevalencia; el reparto de genes a estudio para buscar mutaciones;crear protocolos consensuados de trabajo, y formar a los profesionalesen este campo. Conclusiones. En este suplemento, resultadode un curso de formación, se muestran todos nuestros resultados deestos tres años de trabajo

Introduction. Mental retardation is the most frequent disability and is already quite apparent in infancy. The WorldHealth Organisation (WHO) estimates that it affects approximately 3% of the population in industrialised countries. Amongthe aetiologies that cause mental retardation it would appear that 30% have a genetic origin, although in recent years theprogress made in molecular genetics in relation to new mutations and new genes that can account for mental retardationadvances at an incredible pace. It is for this reason that, three years ago, a group of clinicians and researchers, most of whomwere working in Spain on fragile X syndrome (the most prevalent of the hereditary causes of mental retardation), decided toset up the GIRMOGEN (Genetic Mental Retardation Research Group). Most of us had noticed how many of the clinical casesthat we dealt with went undiagnosed and that the exact prevalence of this disability in Spain was not known either.Development. GIRMOGEN was funded by the Carlos III Health Institute and is made up of eight groups; a ninth group isresponsible for coordinating the work. Its members are all involved in clinical studies or research into mental retardation witha genetic origin, and belong to 15 hospitals and to five universities from a total of 11 different autonomous communities inSpain. Some of its aims include gathering all the data on patients and families in a common database for epidemiological andprevalence studies; distributing genes to be studied in order to search for mutations; creating generally approved workprotocols, and training professionals in this field. Conclusions. In this supplement, which is the result of a training course, wereport all the findings we have obtained in these three years of work

Síndrome de Rett: actualización diagnóstica, clínica y molecular / Rett syndrome: a diagnostic, clinical and molecular update

Introducción. El síndrome de Rett (SR) se describió porprimera vez en 1966 y en el año 1999 se descubrió que estaba asociadocon mutaciones en el gen MECP2. En estos cinco últimos añosse han escrito más de 500 artículos que han evidenciado la complejidady la importancia de este síndrome. Objetivo. Presentar unresumen actualizado en castellano. Desarrollo. El SR es la causamás frecuente de retraso mental en mujeres después del síndrome deDown, con una prevalencia estimada de 1/15.000 niñas en Europa.Es un síndrome de deterioro psicomotor progresivo, con autismo,movimientos estereotipados de las manos, pérdida del lenguaje adquiridoy disminución del crecimiento craneal. Es una patología dominante,ligada al cromosoma X, que en los varones es mayoritariamenteletal y en la que más del 99% de los casos son mutaciones denovo. El gen MECP2 tiene cuatro exones que codifican para dos isoformasdiferentes de una proteína que controla y regula la actividadde otros genes, inhibiendo su transcripción. El estudio molecular delgen MECP2 ha demostrado que el fenotipo clínico del SR es muchomás amplio que el descrito inicialmente con numerosas variantes,tanto con más gravedad como con menos, e incluso con presencia demutaciones en varones y en otros fenotipos no Rett, así como en casosde retraso mental de etiología desconocida. Más recientemente,en las variantes con epilepsia temprana, se han hallado mutacionesen otro gen, el CDKL5. Conclusiones. Los trabajos en estos últimosaños demuestran la enorme complejidad de las enfermedades dedesarrollo neurológico y la necesidad de seguir avanzando en losestudios moleculares

Introduction. Rett syndrome (RS) was first reported in 1966 and in 1999 it was discovered that it was associated tomutations in the MECP2 gene. In the last 5 years over 500 articles have been written on the subject, which is clear evidenceof how complex and important this syndrome is. Aim. To present an updated summary of the topic in Spanish. Development.RS is the second most common cause of mental retardation in females after Down syndrome, with an estimated prevalence of1/15,000 girls in Europe. It is a syndrome involving progressive psychomotor deterioration, with autism, stereotypic movementsof the hands, loss of acquired language and decreased cranial growth. It is a dominant X-linked pathology that is usually fatalin males and in which over 99% of cases involve de novo mutations. The MECP2 gene has four exons that code for twodifferent isoforms of a protein that controls and regulates the activity of other genes by inhibiting their transcription.Molecular studies of the MECP2 gene have shown that the clinical phenotype of RS is far broader than the one initiallydescribed and has numerous variants, which may be either more or less severe, and there are even mutations in males and inother non-Rett phenotypes, as well as in cases of mental retardation in which the aetiology is unknown. More recently, in thevariants with early epilepsy, mutations have been found in another gene –CDKL5. Conclusions. The work carried out in recentyears shows the vast complexity of neurological developmental diseases and illustrates the need to make further progress inmolecular studies

La prevención del síndrome X frágil mediante el diagnóstico prenatal genético: ventajas y aspectos controvertidos / Prevention of fragile X syndrome by prenatal genetic diagnosis: advantages and controversial aspects

Introducción. El síndrome X frágil es la causa más común de retraso mental hereditario. Desde el descubrimiento, hace justo diez años, del mecanismo molecular que lo produce (expansión anómala del triplete CGG en el gen FMR1 e hipermetilación de su isla CpG), el diagnóstico prenatal genético se ha podido ofertar con total fiabilidad a las familias que transmiten el síndrome. Objetivo. Presentar y discutir nuestra experiencia en este campo, desde el año 1994 hasta la actualidad. Pacientes y métodos. Hemos realizado en este período 15 diagnósticos prenatales: 14 en muestras de vellosidades coriales de 13 gestaciones (una de ellas gemelar) y uno en líquido amniótico. En todos ellos hemos utilizado las técnicas moleculares de Southern blotting con la sonda StB12.3, la PCR del triplete CGG y el DXS548 en algunos. Resultados. Nueve fetos fueron normales y, de los otros seis, tres portaban la mutación completa, uno llevaba una deleción del gen FMR1, otro era premutado, y el último llevaba un alelo en la zona gris (50 repeticiones). Conclusiones. El diagnóstico prenatal molecular del SXF es rápido y fiable al 100 por ciento, aunque, desde el punto de vista técnico no es sencillo, y requiere a la vez la utilización de varias técnicas moleculares. Desde el punto de vista clínico, la baja tasa de mutaciones encontradas asegura la procreación, aunque el estudio molecular no predice el estado mental, ni en las niñas con la mutación completa, ni en los niños premutados (AU)