Cerebrospinal fluid concentrations of idebenone in Friedreich ataxia patients

We studied plasma and cerebrospinal fluid (CSF) concentrations of idebenone in five Friedreich ataxia patients on treatment with this antioxidant, and plasma and CSF ubiquinone-10 (Q (10)) concentrations in 15 controls. CSF idebenone concentrations were below the detection limit in 3 Friedreich ataxia patients and no association could be demonstrated between plasma and CSF idebenone values. Q (10) CSF concentrations (median: 2.25 nmol/L) were approximately 300 times lower than those of plasma (median: 0.77 micro mol/L). No correlation was observed between plasma and CSF Q (10) concentrations. A significantly positive correlation was observed between CSF total protein values (range 8.1 - 107.5 mg/dL; median: 29.5) and CSF Q (10) concentrations (Spearman test: r = 0.664; p = 0.01). Our findings suggest that less idebenone is distributed to the brain than to other tissues, although CSF does not appear to be an appropriate material for treatment monitoring of idebenone and other quinoid compounds.

Friedreich's ataxia: idebenone treatment in early stage patients

BACKGROUND

Antioxidant therapy has been applied to Friedreich's ataxia patients. We assessed the effect of idebenone treatment in patients with Friedreich's ataxia.

DESIGN

open-label trial. Nine Friedreich's ataxia patients (age range 11 - 19 years) were treated with idebenone (5 mg/kg/day). Patients were evaluated before the start of the therapy and throughout one year of treatment by International Cooperative Ataxia Rating Scales (ICARS) scores, neurophysiological investigations and echocardiographic measurements. Serum idebenone concentrations were measured by HPLC with electrochemical detection. The number of GAA repeats at the frataxin gene was analyzed by PCR.

RESULTS

Serum idebenone concentrations ranged between 0.04 - 0.37 micro mol/L. Significantly positive correlation was observed between idebenone values and the percentage of difference between the ICARS scores before and 12 months after the start of the therapy (r = 0.883; p = 0.002). Significant reduction was observed comparing the ICARS scores in baseline conditions and after 3 months of treatment (p = 0.017). No differences were observed in echocardiographic measurements after the start of the therapy.

CONCLUSIONS

Cerebellar improvement was notable in mild patients after the first 3 months of therapy. Idebenone treatment at early stages of the disease seems to reduce the progression of cerebellar manifestations. Further blind trials with a greater number of patients and higher doses are needed to fully assess the therapeutic potential of idebenone in Friedreich's ataxia.

Prenatal diagnosis in Rett syndrome

BACKGROUND/AIM

Rett syndrome (RTT) is an X-linked neurodevelopmental dominant disorder that affects almost exclusively girls. The disease is mainly sporadic, caused by de novo mutations at MECP2 gene (Xq28), but a low percentage of familial cases have been reported. We present the results of RTT prenatal diagnosis in three families and discuss the usefulness of such analyses in diseases caused mainly by de novo mutations.

METHODS

For adult individuals, DNA was extracted from peripheral lymphocytes; for fetus analysis it was obtained from cultured amniotic fluid or from chorionic biopsy specimens. Mutation detection at MECP2 gene was first carried out in the patients by SSCP/HD analysis and subsequent sequencing. Family studies and prenatal diagnoses were done by direct analysis of previously characterized patients' mutations using SSCP/HD or restriction analysis.

RESULTS

Heterozygous mutations identified in the 3 patients were: 1061del96bp, 473C-->T, and 763C-->T, respectively. Mutations were not present in the mothers' DNAs obtained from peripheral lymphocytes. None of the 3 fetuses analyzed carried the mutation of the affected sister.

CONCLUSIONS

Recurrence within RTT families can be due to asymptomatic nonpenetrant carrier mothers or to parental germinal mosaicism for the MECP2 mutation. Since germline mosaicism can neither be predicted nor detected, families with 1 affected patient whose RTT-causing mutation has been previously identified can benefit from prenatal diagnosis which contributes to a decrease in the recurrence risk in a new pregnancy comparable to that of the normal population.

Rett syndrome in Spain: mutation analysis and clinical correlations

Rett syndrome (RTT) is an X-linked neurodevelopmental disease that affects girls almost exclusively. In a high proportion of patients the disease is caused by de novo mutations at the MECP2 gene, encoding methyl-CpG-binding protein 2. With the aim to characterize the spectrum of mutations in a series of sporadic RTT patients, including an affected male, and to relate the genetic results to the clinical features of the disease, a clinical checklist and a score system were elaborated to evaluate the clinical severity of the disease. Mutation analysis of the MECP2 coding region was done by direct sequencing. De novo mutations were found in 60% of the patients, including both classic and atypical forms. The change R133H was identified in a 13-year-old boy showing a classic RTT phenotype and normal karyotype. Significant differences were observed among missense and truncating mutations regarding disease severity, age of onset of stereotypies, and the ability of the patients to sit alone and to walk.

dfh is a Drosophila homolog of the Friedreich's ataxia disease gene

A putative Drosophila homolog of the Friedreich's ataxia disease gene (FRDA) has been cloned and characterized; it has been named Drosophila frataxin homolog (dfh). It is located at 8C/D position on X chromosome and is spread over 1kb, a much smaller genomic region than the human gene. Its genomic organization is simple, with a single intron dividing the coding region into two exons. The predicted encoded product has 190 amino acids, being considered a frataxin-like protein on the basis of the sequence and secondary structure conservation when compared with human frataxin and related proteins from other eukaryotes. The closest match between the Drosophila and the human proteins involved a stretch of 38 amino acids at C-terminus, encoded by dfh exon 2, and exons 4 and 5a of the FRDA gene, respectively. This highly conserved region is very likely to form a functional domain with a beta sheet structure flanked by alpha-helices where the sequence is less conserved. A signal peptide for mitochondrial import has also been predicted in the Drosophila frataxin-like protein, suggesting its mitochondrial localization, as occurs for human frataxin and other frataxin-like proteins described in eukaryotes. The Drosophila gene is expressed throughout the development of this organism, with a peak of expression in 6-12h embryos, and showing a spatial ubiquitous pattern from 4h embryos to the last embryonic stage examined. The isolation of dfh will soon make available specific dfh mutants that help in understanding the pathogenesis of FRDA.

Mutation analysis of 16S rRNA in patients with Rett syndrome

Rett syndrome (RTT) is a progressive neurodevelopmental disorder that affects one in 10,000-15,000 females. RTT is mainly sporadic; familial cases have an estimated frequency of less than 1%. Before the recent identification of de novo dominant mutations in the X-linked MECP2 gene, many other hypotheses had been proposed to explain the particular pattern of inheritance and the phenotypic expression of the disease. The involvement of mitochondrial DNA had been investigated because of the structural and functional mitochondrial abnormalities evident in the patients. In 1997 the finding of mutations at 16S rRNA in several affected RTT females and their mothers was reported, suggesting that mitochondrial DNA might play a key role in the pathogenesis of RTT. To investigate the relevance of such mutations, we used the same methodologic approach to analyze RTT mitochondrial DNA in our series. No 16S rRNA alterations were evident in 27 Spanish patients with classic RTT.

Children with stroke: polymorphism of the MTHFR gene, mild hyperhomocysteinemia, and vitamin status

The aim of this study was to investigate a possible association among the thermolabile polymorphism, nucleotide 677 cytosine to thymidine point mutation (677 C-->T) of the methylenetetrahydrofolate reductase (MTHFR) gene, hyperhomocysteinemia, serum folate, vitamins B12 and B6, and stroke in children. Allele and genotype frequencies for the 677 C-->T polymorphism in 21 children with stroke and 28 healthy children of the same age were studied. No differences in allelic frequency were detected between the two populations. However, the prevalence of homozygous 677 C-->T was doubled in the stroke population (28.6%) compared to the healthy group (14.3%). Total plasma homocysteine (tHcy) levels were significantly increased in children aged 2 months to 15 years with stroke compared to reference values. No association was observed between the homozygous genotype (T/T) and hyperhomocysteinemia, nor between the T/T genotype and low folate levels (below the 95th percentile) in this group of patients. Vitamin concentrations in patients were not significantly different from reference values. Significant negative correlations were found between tHcy and folate and between tHcy and cobalamin, but not between tHcy and B6 concentrations. In summary, a higher prevalence of hyperhomocysteinemia and the 677 C-->T polymorphism were observed in children with stroke, but were not always associated. The systematic study of both abnormalities in children with stroke is recommended, so that hyperhomocysteinemia of any genetic origin can be corrected with vitamin supplementation. Moreover, the 677 C-->T genotype is a strong factor for predisposition to hyperhomocysteinemia and recurrent risk of stroke that might also be prevented with folate supplementation.

Anti-epileptic drug treatment in children: hyperhomocysteinaemia, B-vitamins and the 677C-->T mutation of the methylenetetrahydrofolate reductase gene

The aim of the study was to observe the influence of carbamazepine and valproic acid on plasma total homocysteine and B-vitamin status and the gene-drug interaction with the 677C-->T mutation of the methylenetetrahydrofolate reductase (MTHFR) gene. Plasma total homocysteine concentrations were determined in 136 epileptic children taking anti-epileptic drugs as monotherapy. Nutritional (folate, B12 and B6 vitamins) and genetic (MTHFR 677 C-->T) determinants of plasma homocysteine were studied in a random sample of 59 of the 136 epileptic children. Total homocysteine concentrations were significantly increased (p < 0.05) and folate and vitamin B6 levels were significantly decreased (p < 0.01) in the children taking anti-epileptic drugs compared with our reference ranges. In the carbamazepine-treated group, significantly positive correlation was found between duration of treatment and homocysteine concentration (p < 0.01). Homocysteine concentrations showed a significantly negative correlation with vitamin levels (folate: p = 0.002, and vitamin B12: p = 0.017) only in the carbamazepine treated group. In children treated with carbamazepine up to 3 years, total homocysteine concentration correlated negatively only with folate (p = 0.003), while in patients treated for more than 3 years, total homocysteine correlated negatively only with vitamin B12 values (p = 0.007). The lowering action of carbamazepine treatment on folate levels seems to be associated with hyperhomocysteinaemia, which seems to be related to the homozygous condition for the MTHFR 677C-->T mutation. Valproic acid treatment, although also associated with hyperhomocysteinaemia, only shows a lowering effect on vitamin B6 levels, which seems to be independent of the MTHFR genotype.

Genotype and phenotype analysis of Friedreich's ataxia compound heterozygous patients

Friedreich's ataxia is caused by mutations in the FRDA gene that encodes frataxin, a nuclear-encoded mitochondrial protein. Most patients are homozygous for the expansion of a GAA triplet repeat within the FRDA gene, but a few patients show compound heterozygosity for a point mutation and the GAA-repeat expansion. We analyzed DNA samples from a cohort of 241 patients with autosomal recessive or isolated spinocerebellar ataxia for the GAA triplet expansion. Patients heterozygous for the GAA expansion were screened for point mutations within the FRDA coding region. Molecular analyses included the single-strand conformation polymorphism analysis, direct sequencing, and linkage analysis with FRDA locus flanking markers. Seven compound heterozygous patients were identified. In four patients, a point mutation that predicts a truncated frataxin was detected. Three of them associated classic early-onset Friedreich's ataxia with an expanded GAA allele greater than 800 repeats. The other patient associated late-onset disease at the age of 29 years with a 350-GAA repeat expansion. In two patients manifesting the classical phenotype, no changes were observed by single-strand conformation polymorphism (SSCP) analysis. Linkage analysis in a family with two children affected by an ataxic syndrome, one of them showing heterozygosity for the GAA expansion, confirmed no linkage to the FRDA locus. Most point mutations in compound heterozygous Friedreich's ataxia patients are null mutations. In the present patients, clinical phenotype seems to be related to the GAA repeat number in the expanded allele. Complete molecular definition in these patients is required for clinical diagnosis and genetic counseling.

Phenotype correlation and intergenerational dynamics of the Friedreich ataxia GAA trinucleotide repeat

The Friedreich ataxia (FA) mutation has recently been identified as an unstable trinucleotide GAA repeat present 7-22 times in the normal population but amplified as many as > 1,000 times in FA. Since it is an autosomal recessive disease, FA does not show typical features observed in other dynamic mutation disorders, such as genetic anticipation. We have analyzed the GAA repeat in 104 FA patients and 163 carrier relatives previously defined by linkage analysis. The GAA expansion was detected in all patients, most (94%) of them being homozygous for the mutation. We have demonstrated that clinical variability in FA is related to the size of the expanded alleles: milder forms of the disease-late-onset FA and FA with retained reflexes-are associated with shorter expansions, especially with the smaller of the two expanded alleles. Absence of cardiomyopathy is also associated with shorter alleles. Dynamics of the GAA repeat has been investigated in 212 parent-offspring pairs. Meiotic instability showed a sex bias: paternally transmitted alleles tend to decrease in a linear way that depends on the paternal expansion size, whereas maternal alleles can either increase or decrease. A different pattern of intergenerational variation was also observed, depending on the genetic status of the sib: patients had shorter expansions than were seen in heterozygous carriers. This finding has been interpreted as a postzygotic event. Finally, we have observed that the size of the expansion remains constant in the population through carriers.

A family segregating a Friedreich ataxia phenotype that is not linked to the FRDA locus

Friedreich ataxia is an autosomal recessive neurodegenerative disorder. The genetic homogeneity to the FRDA locus on chromosome 9q13-21.1 has been observed in families from different ancestries. We report a Spanish family with two affected and three unaffected children. The segregated classical Friedreich ataxia did not show the expected linkage. The analysis focusses on flanking markers FR1, FR2, FR7 and FR5, excluding linkage 1 cM around the FRDA locus. The unique clinical hallmark in this family was the absence of cardiomyopathy after a long-term follow-up in the two affected children. In both patients serum vitamin E levels were normal. The present observations support the existence of a second locus in Friedreich ataxia, and we suggest that this form could be clinically characterized by the absence of muscular heart disease.

Evidence for a common origin of most Friedreich ataxia chromosomes in the Spanish population

Haplotype analysis is a powerful approach to understand the spectrum of mutations accounting for a disease in a homogeneous population. We show that haplotype variation for 10 markers linked to the Friedreich ataxia locus (FRDA) argues in favor of an important mutation homogeneity in the Spanish population, and positions the FRDA locus in the region where it has been recently isolated. We also report the finding of a new single nucleotide polymorphism called FAD1. The new marker shows a very strong linkage disequilibrium with Friedreich ataxia (FA) in both the Spanish and French populations. suggesting the existence of an ancient and widespread FRDA mutations. Inclusion of FAD1 in the extended haplotype analysis has allowed to postulate that this main FRDA mutation could account for 50-90% of the disease chromosomes. The results indicate that FA, despite clinical heterogeneity, could have originated from a few initial mutations.

Early-onset ataxia with cardiomyopathy and retained tendon reflexes maps to the Friedreich's ataxia locus on chromosome 9q

Absence of lower limb tendon reflexes has been considered an essential diagnostic criterion for Friedreich's ataxia (FA). However, preservation of knee and ankle jerks has been reported in a few patients. Linkage analysis to FA locus (FRDA) on chromosome 9q13-21.1 was performed in 11 patients from 6 families with FA phenotype, including cardiomyopathy, but retained reflexes (FARR). A maximal lod score of 3.38 at recombination fraction theta equal to 0.00 was obtained demonstrating that FARR maps to the FRDA locus. These results suggest that FARR is a variant phenotype of FA.

Mapping of Friedreich's ataxia locus by identification of recombination events in patients homozygous by descent

The Friedreich's ataxia locus (FRDA) maps on chromosome 9q13. Genetic data, obtained from a small number of recombination events, indicated that the FRDA locus might be located centromeric to the D9S15/D9S5 linkage group, the most probable order being cen-FRDA-D9S5-D9S111-D9S15-D9S110-qter. Recently, new centromeric markers have been reported. Analysis of these markers allowed us to localize the recombination breakpoint in some of the recombinant families. However, only one proximal recombination has been found with these markers. To increase the genetic information from FRDA families, we have analyzed the centromeric markers FR1, FR2, FR7, FR8, and FR5 in patients homozygous by descent. These were ascertained because parents were consanguineous or because they were homozygous for the entire haplotype D9S15 or D9S111-D9S5-D9S411E-D9S202. Haplotype divergence for, at least, two contiguous markers was observed in two patients homozygous for the core D9S111-FR2 haplotype and in one third-degree consanguineous family homozygous for haplotype D9S411E-FR5. Interpretation of divergence as the result of ancient meiotic crossovers allowed the definition of three new recombination events which place the FRDA locus within the interval defined by markers D9S411E and FR8. A consanguineous family with first-cousin parents showed homozygosity only at D9S202 and FR2. Further investigations are needed to discern whether two different mutations are segregating in the family or whether two recombinations, one distal and one proximal, have taken place.