Search

Rett syndrome is a monogenic X-linked dominant neurodevelopmental disorder related to mutation in MECP2, which encodes the methyl-CpG–binding protein MeCP2. The aim of this study was to search for mutations of MECP2 gene in Tunisian Rett patients and to evaluate the impact of the found variants on structural and functional features of MeCP2. The result of mutation analysis revealed that 3 Rett patients shared the same novel heterozygous point mutation c.175G>C (p.A59P). The p.A59P mutation was located in a conserved amino acid in the N-terminal segment of MeCP2. This novel mutation confers a phenotypic variability with different clinical severity scores (3, 8, and 9) and predicted by Sift and PolyPhen to be damaging. Modeling results showed that p.A59P adds 2 hydrogen bonds and changes the structural conformation of MeCP2 with a significant root mean square deviation value (9.66 Å), suggesting that this mutation could probably affect the conformation, function and stability of MeCP2.

Rett syndrome is an X-linked neurodevelopmental disorder, primarily caused by MECP2 mutations. In this study, clinical, molecular and bioinformatics analyses were performed in Rett patients to understand the relationship between MECP2 mutation type and the clinical severity. Two double MeCP2 mutations were detected: a novel one (p.G185 V in cis with p.R255X) in P1 and a known one (p.P179 S in cis with p.R255X) in P2. Besides, a novel synonymous mutation (c.807C>T; p.G269G), which could affect mRNA splicing, was identified in P3. The results from clinical severity analysis have shown that P1 was more severely affected than P2 with CSS being 35 and 14, respectively. Therefore, the phenotypic variability in P1 and P2 could be explained by the potential pathogenic effect of the RTT-causing missense mutation p.G185 V in the AT-hook1. In conclusion, clinical, molecular, and in silico investigations in the studied patients have been proven to be substantial for the genotype-phenotype correlation.

Rett syndrome (RTT) is a severe neurodevelopmental disorder affecting almost exclusively girls. Rett patients present an apparently normal psychomotor development during the first 6–18 months of life. Thereafter, they show a short period of developmental stagnation followed by a rapid regression in language and motor development. RTT is currently considered as monogenic X-linked dominant disorder due to mutations in the MECP2 gene, encoding the methyl-CpG binding protein 2. The aim of this study was to perform a mutational analysis of the MECP2 gene in a classical Rett patient.The results showed the presence of a novel point mutation c.C1142T (p.P381L) and two deletions at the heterozygous state: a novel deletion c.1075delTTC (p.S359) and a known one c.1157del44 (p.L386Q fs X2) in the C-terminal region of MeCP2.

Rett syndrome (RTT), an X-linked dominant neurodevelopmental disorder in females, is caused mainly by de novo mutations in the methyl-CpG-binding protein 2 gene ( MECP2). Rett patients present an apparently normal psychomotor development during the first 6 to 18 months of life. Thereafter, they show a short period of developmental stagnation followed by a rapid regression in language and motor development. In the present study, we performed a mutational analysis of the MECP2 gene in 2 typical Rett syndrome patients and in 1 atypical Rett syndrome girl. The results showed the presence of 3 de novo point mutations in the C-terminal region: 2 novel mutations: c.1065C>A (p.S355R) and c.1030C>G (p.R344G) in the 2 typical Rett syndrome girls, but also the c.996C>T (p.S332S) mutation first described in the atypical Rett syndrome patient.

Highlights: {yields} Sequencing of the MECP2 gene, modeling and comparison of the two variants were performed in a Tunisian classical Rett patient. {yields} A double-mutation: a new and de novo mutation c.535C > T and the common one c.763C > T of the MECP2 gene was identified. {yields} The P179S transition may change local electrostatic properties which may affect the function and stability of the protein MeCP2. -- Abstract: Rett syndrome is an X-linked dominant disorder caused frequently by mutations in the methyl-CpG-binding protein 2 gene (MECP2). Rett patients present an apparently normal psychomotor development during the first 6-18 months of life. Thereafter, they show a short period of developmental stagnation followed by a rapid regression in language and motor development. The aim of this study was to perform a mutational analysis of the MECP2 gene in a classical Rett patient by sequencing the corresponding gene and modeling the found variants. The results showed the presence of a double-mutation: a new and de novo mutation c.535C > T (p.P179S) and the common c.763C > T (p.R255X) transition of the MECP2 gene. The p.P179S mutation was located in a conserved amino acid in CRIR domain (corepressor interacting region). Modeling results showedmore » that the P179S transition could change local electrostatic properties by adding a negative charge due to serine hydroxyl group of this region of MeCP2 which may affect the function and stability of the protein. The p.R255X mutation is located in TRD-NLS domain (transcription repression domain-nuclear localization signal) of MeCP2 protein.« less

Background: Febrile seizures (FSs) relatively represent the most common form of childhood seizures. FSs are not thought of as a true epileptic disease but rather as a special syndrome characterized by its provoking factor (fever) and a typical range of 3 months to 5 years. Although specific genes affecting the majority of FS cases have not been identified yet, several genetic loci for FSs have been reported recently. The aim of this report is to search for the gene responsible for FSs in six affected Tunisian families. Methods: A microsatellite marker analysis was performed on the known FS and generalized epilepsy with febrile seizures plus (GEFS+) loci. According to the results obtained by statistical analyses for the six studied families and in agreement with the involvement of SCN1B gene in the GEFS+ syndrome in previous studies, SCN1B on GEFS+1 locus was considered as one of the potential candidate genes and was tested for mutations by direct sequencing. Results: A sequencing analysis of the SCN1B gene revealed a novel mutation (c.374G>T) that changed an arginine residue with leucine at position 125 of the protein. We consider that the variation R125L may affect the protein structure and stability by the loss of hydrogen bonding. Two identified single nucleotide polymorphisms that are located in a neighboring hypothetical polyadenylation were assumed to compose a putative disease-associated haplotype. Conclusion: Our results support that SCN1B is the gene responsible in one amongst the six FS Tunisian families studied and might contribute to the FS susceptibility for the five others.

Rett syndrome is a severe disorder characterized by loss of acquired skills after a period of normal development in infant girls. It is caused mainly by mutations in the MECP2 gene. In this study, we reported mutations in the MECP2 gene in 7 Tunisian patients with classic Rett syndrome. The results showed the presence of a double mutation in 1 patient: p.R306C and c.1461+98insA, which create a new hypothetical polyadenylation site in the 3′UTR of the MECP2 gene. We also detected in another patient a new variant c.1461+92C>G in the 3′UTR located previous to 34 bp from the polyadenylation site with a score of 4.085. This variation is located in a hypothetical splicing enhancer with a score of 1.96277 according to the ESE finder program. In the remaining 5 patients, we found 2 common mutations: p.T158M in 4 individuals and p.R168X in only 1 girl.

Background and purpose: Febrile Seizure can be associated with heterogeneous epilepsy phenotypes regrouped in a syndrome called generalized epilepsy with febrile seizures plus (GEFS+). The aim of this report is to search for the gene responsible for GEFS+ in two affected Tunisian families. Methods: Microsatellite marker analysis was performed on the known FS and GEFS+ loci. According to the results obtained by statistical analyses, GABRG2 on GEFS+3 locus and SCN1A on GEFS+2 locus were considered as two of the potential candidate genes and were tested for mutations by direct sequencing. Results and conclusions: The mutation analysis and statistical test of the GABRG2 gene revealed a disease association with rs211014 in intron 8 (χ2 = 5.25, P = 0.021). A sequencing analysis of the SCN1A gene was performed for the two tested families and showed a known mutation (c.1811G>A) and a putative disease-associated haplotype in only one family. Our results support that SCN1A is the responsible gene for GEFS+ in one of the two studied Tunisian families and suggest a positive association of an intronic SNP in the GABRG2 gene in both families.

Patients with classical Rett show an apparently normal psychomotor development during the first 6-18 months of life. Thereafter, they enter a short period of developmental stagnation followed by a rapid regression in language and motor development. Purposeful hand use is often lost and replaced by repetitive, stereotypic movements. Rett syndrome (RTT) is an X-linked dominant disorder caused frequently by mutations in the methyl-CpG-binding protein 2 gene (MECP2). The aim of this study was to search for mutations in MECP2 gene in two Tunisian patients affected with RTT. The results of mutation analysis revealed mutations in exon 4 of MECP2 gene in the two patients. In one patient we identified a new mutation consisting of a deletion of four bases (c.810-813delAAAG), which led to a frame shift and generated a premature stop codon (p.Lys271Arg fs X15) in transcriptional repression domain-nuclear localization signal (TRD-NLS) domain of MeCP2 protein. With regard to the second patient, a previously described transition (c.916CT) that changed an arginine to a cysteine residue (p.R306C) in TRD domain of MeCP2 protein was revealed. In conclusion, a new and a known de novo mutation in MECP2 gene were revealed in two Tunisian patients affected with RTT.

Mitochondria are essential for early cardiac development and impaired regulation of mitochondrial function was implicated in congenital heart diseases. We described a newborn girl with hypertrophic cardiomyopathy and profound hearing loss. The mtDNA mutational analysis revealed the presence of known polymorphisms associated to cardiomyopathy and/or hearing loss, and 2 novel heteroplasmic mutations: m.3395A>G (Y30C) occurring in a highly conserved aminoacid of the ND1 gene and the m.4316A>G located in the residue A54 of the tRNA(Ile) gene. These 2 novel variations were absent in 150 controls. All these variants may act synergistically and exert a cumulative negative effect on heart function to generate the cardiomyopathy.

LGMD (limb-girdle muscular dystrophy) and CMD (congenital muscular dystrophy) are two common forms of neuromuscular disorders which are distinguishable by their age of onset but with probably a similar underlying pathway. In the present study, we report immunohistochemical, Western-blot and genetic analyses in a large consanguineous Tunisian family with two branches, including seven patients sharing similar LGMD2 phenotype in one branch and one CMD patient in the other branch. Linkage analyses were compatible with the LGMD2A locus in one branch and the MDC1A (muscular dystrophy congenital type 1A) locus in the other branch. This result was supported by deficiency in merosin and calpain3 in the CMD patient and LGMD patients respectively. Mutation analysis revealed two distinct mutations: a c.8005delT frameshift deletion in exon 56 of the LAMA2 (laminin-α2) gene (MDC1A) was found in the CMD patient and a new homozygous mutation c.1536+1G>T in the donor splice site of intron 12 of the CAPN3 (calpain3) gene (LGMD2A) was found in the LGMD patients. RT–PCR (reverse transcription–PCR) performed on total RNA from a LGMD2A patient's muscle biopsy showed complete retention of intron 12 in CAPN3 cDNA, generating a PTC (premature termination codon) that potentially elicits degradation of the nonsense mRNA by NMD (nonsense-mediated mRNA decay). Our results indicate that mRNA analysis is necessary to clarify the primary effect of genomic mutations on splicing efficiency that alters mRNA processing and expression level.

Generalized epilepsy with febrile seizure plus (GEFS+) is an autosomal dominant disorder. In the literature, 5 responsible genes were identified and 2 novel susceptibility loci for GEFS+ at 2p24 and 8p23-p21 were reported, indicating the genetic heterogeneity of this disorder. The aim of this report is to identify the responsible loci in a large affected Tunisian family by performing a 10cM density genome-wide scan. The highest multipoint logarithm of odds (LOD) score (1.04) was found for D5S407 in the absence of recombination. Two other interesting regions were found around marker D19S210 (LOD=0.799) and D7S484 (LOD=0.61) markers. To fine map these loci, additional markers in 2 regions on 5q13.3 and 7p14.2 were analyzed and positive LOD scores for both loci were obtained. Sequencing of the Sodium channel subunit beta-1 gene (SCN1B) (19q13.1) showed the absence of any causal mutation. Our findings emphasized the genetic heterogeneity of febrile seizures.

Inherited factor XIII (FXIII) deficiency is a rare bleeding disorder characterized by an umbilical bleeding during the neonatal period, delayed soft tissue bruising, mucosal bleeding spontaneous intracranial hemorrhage, and soft tissue hemorrhages. Congenital FXIII deficiency is an autosomal recessive disorder, usually attributed to a defect in the FXIIIA and B subunits coding, respectively, by F13A and F13B genes. The aim of this study was to determine the molecular defects responsible for congenital factor XIII deficiency in eight Tunisian families. Molecular analysis was performed by direct DNA sequencing of polymerase chain reaction amplified fragments spanning the coding regions and splice junctions of the FXIIIA subunit gene (F13A) in probands and in families' members and compared with the reported sequence of this gene. In all patients, FXIIIA activity was undetectable and the FXIIIB was within the normal range. Direct sequencing of the F13A gene in all probands showed two mutations: the c.869insC mutation found in eight patients and the c.1226G > A transition found in only one. We also confirmed the presence of a founder effect for the first frequent mutation by using two microsatellite markers, HUMF13A01 and a generated ployAC marker (HUMF13A02). We describe here molecular abnormalities found in nine Tunisian probands diagnosed with FXIIIA deficiency. The identification of the founder mutation and polymorphisms allowed a genetic counseling in relatives of these families, and the antenatal diagnosis is now available.

Rett syndrome (RTT) whose major cause is the mutations in the X-linked MECP2 gene is a genetic disease that affects females. We screened two RTT patients using cytogenetic studies and in silico analysis as well as molecular analysis by the direct sequencing of MECP2. The cytogenetic results showed that although patient A was karyotypically normal, patient B showed chromosomal abnormalities, including chromosomal breakage in both chromosomes 2 and 5. In addition, chromosome 9 was detected on heteromorphic pattern (9ph+). A significant increase in sister-chromatid exchange (SCE) frequency was also observed in this patient. Although both patients were karyotypically different, they share the same MeCP2 mutation (p.P152R) which was predicted to be deleterious. To our knowledge, we describe the first association between MECP2 mutation, chromosomal abnormalities and high SCE frequency, which further validates the importance of the thorough chromosomal and molecular analyses that should be performed on the suspected RTT cases.