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.

Detection of new pathogenic mutations in patients with congenital haemolytic anaemia using next-generation sequencing.

INTRODUCTION: Congenital haemolytic anaemia (CHA) refers to a group of genetically heterogeneous disorders, mainly caused by changes in genes encoding globin chains, cytoskeletal proteins and red cell enzymes, in which accurate diagnosis can be challenging with conventional techniques. METHODS: To set-up a comprehensive assay for detecting mutations that could improve aetiological diagnosis, we designed a custom panel for sequencing coding regions from 40 genes known to be involved in the pathogenesis of CHA, using the Ion Torrent™ (Thermo Fisher Scientific, S.L. Waltham, MA, USA) Personal Genome Machine (PGM) Sequencer. A control group of 16 samples with previously known mutations and a test group of 10 patients with unknown mutations were included for assay validation and application, respectively. RESULTS: In the test group, we identified pathogenic mutations in all cases: four patients had novel mutations in genes related to membrane defects (SPTB, ANK1, SLC4A1 and EPB41), four were homozygous or compound heterozygous for mutations in genes related to enzyme deficiencies (GPI, TPI1 and GSS), one had a mutation in the HBB gene and another presented a homozygous mutation in the ADAMTS13 gene. CONCLUSIONS: Ion PGM sequencing with our custom panel is a highly efficient way to detect mutations causing haemolytic anaemia, including new variations. It is a high-throughput detection method that is ready for application in clinical laboratories.

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.

Xq28 duplications including MECP2 in five females: Expanding the phenotype to severe mental retardation.

Duplications leading to functional disomy of chromosome Xq28, including MECP2 as the critical dosage-sensitive gene, are associated with a distinct clinical phenotype in males, characterized by severe mental retardation, infantile hypotonia, progressive neurologic impairment, recurrent infections, bladder dysfunction, and absent speech. Female patients with Xq duplications including MECP2 are rare. Only recently submicroscopic duplications of this region on Xq28 have been recognized in four females, and a triplication in a fifth, all in combination with random X-chromosome inactivation (XCI). Based on this small series, it was concluded that in females with MECP2 duplication and random XCI, the typical symptoms of affected boys are not present. We present clinical and molecular data on a series of five females with an Xq28 duplication including the MECP2 gene, both isolated and as the result of a translocation, and compare them with the previously reported cases of small duplications in females. The collected data indicate that the associated phenotype in females is distinct from males with similar duplications, but the clinical effects may be as severe as seen in males.

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.

Differences in the frequency and distribution of BRCA1 and BRCA2 mutations in breast/ovarian cancer cases from the Basque country with respect to the Spanish population: implications for genetic counselling.

The prevalence of unique and recurrent BRCA1 and BRCA2 pathogenic mutations and unclassified variants varies among different populations. Two hundred and thirty-six breast and/or ovarian cancer patients were analysed to clarify the role of these genes in the Basque Country. We also studied 130 healthy women from the general population from the same region. Fifteen different pathological mutations were found in 16 index cases: 10 truncating mutations, 4 missense mutations and 1 splicing mutation. c.3002_3003insT and c.5788_5789delGT, both in exon 11 of BRCA2 have not previously been described. No pathological mutations were found in cases of sporadic juvenile breast cancer. There are no recurrent mutations in our population; apart from the mutation c.9254_9258del5, which appears in only two index cases. We have also found a lot of variants whose effect is unknown. From these variants, 17 have not previously been described: 6 missenses, 6 synonymous and 5 alterations in intronic regions. We would like to highlight the fact that 14.3% of patients with 3 or more cases of breast cancer in the family, and 16.7% of patients with family history of breast and ovarian cancer, present a pathological mutation in BRCA1 or BRCA2. This manuscript demonstrates that each population can have different mutations and due to this, Genetic Counselling and selection criteria must be different for each population. Furthermore, this article describes for the first time some new mutations and unclassified variants found in our population.

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.

[Genetic mental retardation. Presentation of the GIRMOGEN network]. / Retraso mental de origen genetico. Presentacion de la Red GIRMOGEN.

INTRODUCTION: Mental retardation is the most frequent disability and is already quite apparent in infancy. The World Health Organisation (WHO) estimates that it affects approximately 3% of the population in industrialised countries. Among the aetiologies that cause mental retardation it would appear that 30% have a genetic origin, although in recent years the progress made in molecular genetics in relation to new mutations and new genes that can account for mental retardation advances at an incredible pace. It is for this reason that, three years ago, a group of clinicians and researchers, most of whom were working in Spain on fragile X syndrome (the most prevalent of the hereditary causes of mental retardation), decided to set up the GIRMOGEN (Genetic Mental Retardation Research Group). Most of us had noticed how many of the clinical cases that 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 is responsible for coordinating the work. Its members are all involved in clinical studies or research into mental retardation with a genetic origin, and belong to 15 hospitals and to five universities from a total of 11 different autonomous communities in Spain. Some of its aims include gathering all the data on patients and families in a common database for epidemiological and prevalence studies; distributing genes to be studied in order to search for mutations; creating generally approved work protocols, and training professionals in this field. CONCLUSIONS: In this supplement, which is the result of a training course, we report all the findings we have obtained in these three years of work.

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

INTRODUCTION: Rett syndrome (RS) was first reported in 1966 and in 1999 it was discovered that it was associated to mutations in the MECP2 gene. In the last 5 years over 500 articles have been written on the subject, which is clear evidence of 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 of 1/15,000 girls in Europe. It is a syndrome involving progressive psychomotor deterioration, with autism, stereotypic movements of the hands, loss of acquired language and decreased cranial growth. It is a dominant X-linked pathology that is usually fatal in males and in which over 99% of cases involve de novo mutations. The MECP2 gene has four exons that code for two different 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 initially described and has numerous variants, which may be either more or less severe, and there are even mutations in males and in other non-Rett phenotypes, as well as in cases of mental retardation in which the aetiology is unknown. More recently, in the variants with early epilepsy, mutations have been found in another gene--CDKL5. CONCLUSIONS: The work carried out in recent years shows the vast complexity of neurological developmental diseases and illustrates the need to make further progress in molecular studies.

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

INTRODUCTION: Fragile X syndrome is the most common cause of hereditary mental retardation. Since the molecular mechanism causing it (anomalous expansion of the CGG triplet in the FMR1 gene and hypermethylation of its CpG island) was identified exactly ten years ago, it has been possible to give families in whom the syndrome is transmitted completely reliable prenatal genetic diagnosis of this. OBJECTIVE: To report and discuss our experience in this field from 1994 to the present time. PATIENTS AND METHODS: During this period we performed 15 prenatal diagnoses: 14 in samples of chorionic villi from 13 pregnancies (one a twin pregnancy) and 1 using amniotic fluid. In all cases we used Southern blot molecular techniques with the StB12.3 probe, the PCR of CGG triplet and DXS548 in some cases. RESULTS: Nine fetuses were normal. Of the other six foetuses, three had full mutation, one had deletion of the FMR1 gene, another was premutated and another had an allele in the grey zone (50 repetitions). CONCLUSIONS: Molecular prenatal diagnosis of SXF is fast and 100% reliable, although from the technical point of view it is complicated and requires use of various molecular techniques. From the clinical point of view, the low rate of mutations found assures offspring, although molecular studies do not predict mental 'status' in either girls with complete mutation or children with permutation.

Molecular study of the rhodopsin gene in retinitis pigmentosa patients in the Basque Country.

Retinitis pigmentosa (RP) is a degenerative disorder affecting the outer segment of the retina and leading to night blindness and progressive visual field loss. The rhodopsin gene encodes a photolabile pigment located in the rod outer segments constituting around 80-90% of its protein content and is the initiation point for the visual cascade upon absorption of a single photon. Seventy-five unrelated, isolated RP families in the Basque Country, with at least one affected member, were diagnosed at our hospital after ophthalmic examination and electroretinogram analysis. The patients received genetic counselling according to their individual case based on their clinical diagnosis. The modes of inheritance found from pedigree studies were the following: 20% (15/75) were classified as autosomal dominant retinitis pigmentosa (ADRP), 17.33% (13/75) were autosomal recessive (ARRP), 2.66% (2/75) were unclassified (NC), and 60% (45/75) were sporadic cases (SCRP). From these families, 75 unrelated and affected index cases together with 22 affected relatives and 42 unaffected relatives were screened for mutations in the rhodopsin gene by GC clamped denaturing gradient gel electrophoresis. Our results showed that five ADRP, three ARRP, 15 SCRP, and one NC families had alterations in this gene. Only three of these alterations, that is 4% (3/75) (95% CL 0-8), appeared to be responsible for the disease. This represents a lower percentage than the 10% previously reported.

Identification by molecular diagnosis of mosaic Turner's syndrome in an obligate carrier female for fragile X syndrome.

A case of mosaic Turner's syndrome with a 45,X/46,XX/47,XXX karyotype, who was also a fragile X obligate carrier as the mother of an affected boy, was identified by molecular diagnosis. Complete haplotyping and direct DNA analysis showed that the X chromosome in all metaphases was the normal X. At the age of 57, she is mentally normal. Her external appearance was typical of Turner's syndrome. This report shows that molecular studies in conjunction with cytogenetic analysis can help in the clinical diagnosis of a rare case and can show the uniqueness of a case such as the one here described.

A further prenatal diagnosis of mosaic tetrasomy 12p (Pallister-Killian syndrome)

A case of mosaic tetrasomy 12p was detected in amniotic fluid cell cultures from a 28-year-old woman referred to us at 26 weeks' gestation because of hydramnios. The fetus was shown on ultrasonography to have an omphalocele and a short femur length. Labour was induced at 32 weeks. An infant with multiple congenital anomalies was delivered and died after 10 min. The diagnosis of i(12p) or Pallister-Killian syndrome was confirmed cytogenetically in fibroblast and lymphocyte cultures. Increased LDH-B activity was demonstrated in fibroblasts.

Factors associated with premature chromosome condensation (PCC) following in vitro fertilization.

From January 1989 to July 1990 a total of 562 oocytes was fixed in our In Vitro Fertilization Program, while cytogenetic data were collected in the case of 433. Forty-eight of these (11%) had a set of oocyte chromosomes in metaphase II, and at least one other set of sperm chromosomes prematurely condensed in the form of single chromatids. In the literature this phenomenon, frequent in our experience, has not been separately studied by many authors. Comparative studies with diverse parameters have shown a significant correlation between the same phenomenon and the use of follicle-stimulating hormone supplementation in ovarian stimulation protocols. Also, in some cases we found a high percentage of repetition of the phenomenon in one patient.

Chromosome studies in human unfertilized oocytes and uncleaved zygotes after treatment with gonadotropin-releasing hormone analogs.

OBJECTIVE: To determine the frequency of the anomalies from the cytogenetic point of view in the oocytes remaining from our in vitro fertilization (IVF) program. Two gonadotropin-releasing hormone analogs (GnRH-a) were used (buserelin acetate and leuprolide acetate) in the superovulation treatment. DESIGN: A prospective study was planned in January 1989. Deadline for data and quantitative analysis was to be July 1990. SETTING: Hospital de Cruces, a public and tertiary institute. PATIENTS: One hundred thirty-nine IVF patients, yielding 433 oocytes. Selected on the basis of availability of oocytes and staff. RESULTS: Two hundred thirty-eight oocytes (71.25%) exhibited the normal number of metaphase II chromosomes; 64 (19.16%) exhibited aneuploidy; 13 (3.89%) were diploid, hyperdiploid, or hypodiploid; and 19 (5.68%) showed parthenogenetic activation. Of the 99 zygotes, 17 were polyploid and 48 showed prematurely condensed chromosomes, whereas in 31 cases the male and female pronuclei remained separate. CONCLUSIONS: It would not appear that the rate of chromosomal anomalies is affected after pituitary suppression with GnRH-a.