Different phenotypes of Friedreich's ataxia within one 'pseudo-dominant' genealogy: relationships between trinucleotide (GAA) repeat lengths and clinical features

Atypical Features in a Large Turkish Family Affected with Friedreich Ataxia

Here, we describe the clinical features of several members of the same family diagnosed with Friedreich ataxia (FRDA) and cerebral lesions, demyelinating neuropathy, and late-age onset without a significant cardiac involvement and presenting with similar symptoms, although genetic testing was negative for the GAA repeat expansion in one patient of the family. The GAA repeat expansion in the frataxin gene was shown in all of the family members except in a young female patient. MRI revealed arachnoid cysts in two patients; MRI was consistent with both cavum septum pellucidum-cavum vergae and nodular signal intensity increase in one patient. EMG showed demyelinating sensorimotor polyneuropathy in another patient. The GAA expansion-negative 11-year-old female patient had mental-motor retardation, epilepsy, and ataxia. None of the patients had significant cardiac symptoms. Description of FRDA families with different ethnic backgrounds may assist in identifying possible phenotypic and genetic features of the disease. Furthermore, the genetic heterogeneity observed in this family draws attention to the difficulty of genetic counseling in an inbred population and to the need for genotyping all affected members before delivering comprehensive genetic counseling.

'Pseudo-Dominant' Inheritance in Friedreich's Ataxia: Clinical and Genetic Study of a Brazilian Family

Friedreich's ataxia (FA) is an autosomal recessive inherited disorder characterized by progressive gait and limb ataxia, hypertrophic cardiomyopathy, limb muscular weakness, and areflexia with positive extensor plantar response. Loss of vibratory and position sense, skeletal abnormalities, and dysarthria are common comorbid features. The wide spectrum of disease may lead to a diagnostic challenge, and in such a scenario, the inheritance pattern might be a clue to diagnosis. A rare and peculiar pattern observed in some families is the pseudodominant pattern that is usually characterized by phenotypic variation, which, in turn, could make it even harder to get to a correct diagnosis. This pattern, although seemingly similar to a true dominant pattern of inheritance, should be kept in mind whenever one is evaluating a family with FA. We evaluated a Brazilian family of Italian ancestry with variation of phenotype among affected siblings.

Friedreich ataxia: molecular mechanisms, redox considerations, and therapeutic opportunities

Mitochondrial dysfunction and oxidative damage are at the origin of numerous neurodegenerative diseases like Friedreich ataxia and Alzheimer and Parkinson diseases. Friedreich ataxia (FRDA) is the most common hereditary ataxia, with one individual affected in 50,000. This disease is characterized by progressive degeneration of the central and peripheral nervous systems, cardiomyopathy, and increased incidence of diabetes mellitus. FRDA is caused by a dynamic mutation, a GAA trinucleotide repeat expansion, in the first intron of the FXN gene. Fewer than 5% of the patients are heterozygous and carry point mutations in the other allele. The molecular consequences of the GAA triplet expansion is transcription silencing and reduced expression of the encoded mitochondrial protein, frataxin. The precise cellular role of frataxin is not known; however, it is clear now that several mitochondrial functions are not performed correctly in patient cells. The affected functions include respiration, iron-sulfur cluster assembly, iron homeostasis, and maintenance of the redox status. This review highlights the molecular mechanisms that underlie the disease phenotypes and the different hypothesis about the function of frataxin. In addition, we present an overview of the most recent therapeutic approaches for this severe disease that actually has no efficient treatment.

A benign congenital myopathy in an inbred Samaritan family

We describe a novel form of myopathy in a mother and her two daughters from an inbred Samaritan family. The patients displayed severe neonatal hypotonia, lethargy and dysmorphic features. Motor milestones were delayed; however, the hypotonia and muscle weakness gradually improved during the first 2 years of life and independent walking was achieved by 18 months. The mother at the age of 23 years shows myopathic facies and minimal proximal weakness. Her intelligence is normal. Her muscle biopsy revealed central nuclei and disruption of the intermyofibrillary network with moth eaten and spiral fibers. Mutations in SMN, MTM1 and the myotonic dystrophy genes were excluded. We suggest this is a new benign form of congenital myopathy. Inheritance is probably autosomal recessive.

Friedreich's ataxia: treatment within reach

Friedreich's ataxia (FA) is the most prevalent cerebellar ataxia in children and adults in Europe. FA is one of a growing number of diseases known to be caused by triplet-repeat expansions. The causative mutation is a GAA trinucleotide-repeat expansion in the first intron of the frataxin gene. The mitochondrial localisation of frataxin and decreased oxidation activity in vivo and in vitro show that FA is a mitochondrial disease. Frataxin is involved in iron metabolism and may protect mitochondria from oxidative damage. The understanding of the disease has only just begun and possible treatments are within reach. In this review I discuss the clinical knowledge of FA and recent developments that have helped to elucidate the pathogenesis of the disease and made the first therapeutic attempts possible.

Evidence for pseudodominant inheritance of atrichia with papular lesions

Atrichia with papular lesions is a rare form of total alopecia, in which mutations in the hairless gene have been shown to underlie the phenotype. In the literature to date, atrichia with papular lesions has generally been reported to be inherited in an autosomal recessive manner. A few rare cases exist, however, in which parent-to-child transmission of atrichia with papular lesions has been documented. In this study, further investigations were carried out into the molecular basis of atrichia with papular lesions in a family with mother-to-son transmission by searching for mutations in the human hairless gene. Specific ally, we wanted to determine whether this case truly represented an example of dominantly inherited atrichia with papular lesions, or whether another mode of inheritance might be responsible for the disorder in this kindred. Pseudodominant inheritance, for example, occurs when an individual with a known recessive disorder has a clinically unaffected partner, but then unexpectedly gives birth to children who are affected with the same recessive disorder as the affected parent, and can easily be distinguished from classical dominant inheritance with molecular diagnosis and haplotype analysis. In the family reported here, we have determined that both the mother and son are, in fact, homozygous for a novel mutation in the hairless gene, R33X. We provide the first evidence for pseudodominant inheritance in atrichia with papular lesions, and at the same time extend our knowledge of pathogenetic mutations in the human hairless gene. Importantly, this information allows revisions in genetic counseling for risk of transmission for individuals in the family, previously impossible in the absence of knowing the genetic basis of atrichia with papular lesions in this unusual kindred.

Near infrared muscle spectroscopy in patients with Friedreich's ataxia

Friedreich's ataxia is a progressive neurodegenerative disorder of the afferent cerebellar pathways associated with mitochondrial dysfunction at the cellular level. We have used noninvasive continuous near infrared muscle spectroscopy (NIRS) to investigate the delivery and utilization of oxygen in response to exercise in this disorder. Patients performed an incremental treadmill walking protocol in which levels of muscle deoxygenation or oxygenation were continuously measured in the medial calf muscle. The kinetics of recovery from exercise-induced deoxygenation, called the half-time of recovery (t(1/2)) were determined. The t(1/2) was prolonged in patients with Friedreich's ataxia compared with controls, and the degree of prolongation correlated with the length of the shorter GAA repeat, a genetic measure that correlates with the age of onset of disease. The t(1/2) also correlated inversely with patient age and with the maximum treadmill speed attained. Several patients also displayed features consistent with inadequate oxygen utilization by muscle. These results suggest that NIRS may be an effective tool for monitoring the biochemical and functional features of Friedreich's ataxia in parallel.