Carmen Espinós

USH3A transcripts encode clarin-1, a four-transmembrane-domain protein with a possible role in sensory synapses

Usher syndrome type 3 (USH3) is an autosomal recessive disorder characterised by the association of post-lingual progressive hearing loss, progressive visual loss due to retinitis pigmentosa and variable presence of vestibular dysfunction. Because the previously defined transcripts do not account for all USH3 cases, we performed further analysis and revealed the presence of additional exons embedded in longer human and mouse USH3A transcripts and three novel USH3A mutations. Expression of Ush3a transcripts was localised by whole mount in situ hybridisation to cochlear hair cells and spiral ganglion cells. The full length USH3A transcript encodes clarin-1, a four-transmembrane-domain protein, which defines a novel vertebrate-specific family of three paralogues. Limited sequence homology to stargazin, a cerebellar synapse four-transmembrane-domain protein, suggests a role for clarin-1 in hair cell and photoreceptor cell synapses, as well as a common pathophysiological pathway for different Usher syndromes.

Autosomal recessive cerebellar ataxias

Autosomal recessive cerebellar ataxias (ARCA) are a heterogeneous group of rare neurological disorders involving both central and peripheral nervous system, and in some case other systems and organs, and characterized by degeneration or abnormal development of cerebellum and spinal cord, autosomal recessive inheritance and, in most cases, early onset occurring before the age of 20 years. This group encompasses a large number of rare diseases, the most frequent in Caucasian population being Friedreich ataxia (estimated prevalence 2–4/100,000), ataxia-telangiectasia (1–2.5/100,000) and early onset cerebellar ataxia with retained tendon reflexes (1/100,000). Other forms ARCA are much less common. Based on clinicogenetic criteria, five main types ARCA can be distinguished: congenital ataxias (developmental disorder), ataxias associated with metabolic disorders, ataxias with a DNA repair defect, degenerative ataxias, and ataxia associated with other features. These diseases are due to mutations in specific genes, some of which have been identified, such as frataxin in Friedreich ataxia, α-tocopherol transfer protein in ataxia with vitamin E deficiency (AVED), aprataxin in ataxia with oculomotor apraxia (AOA1), and senataxin in ataxia with oculomotor apraxia (AOA2). Clinical diagnosis is confirmed by ancillary tests such as neuroimaging (magnetic resonance imaging, scanning), electrophysiological examination, and mutation analysis when the causative gene is identified. Correct clinical and genetic diagnosis is important for appropriate genetic counseling and prognosis and, in some instances, pharmacological treatment. Due to autosomal recessive inheritance, previous familial history of affected individuals is unlikely. For most ARCA there is no specific drug treatment except for coenzyme Q10 deficiency and abetalipoproteinemia.

Cerebellar ataxia with coenzyme Q10 deficiency: diagnosis and follow-up after coenzyme Q10 supplementation.

UNLABELLED Our aim was to report a new case with cerebellar ataxia associated with coenzyme Q10 (CoQ) deficiency, the biochemical findings caused by this deficiency and the response to CoQ supplementation. PATIENT A 12-year-old girl presenting ataxia and cerebellar atrophy. BIOCHEMICAL STUDIES: Coenzyme Q10 in muscle was analysed by HPLC with electrochemical detection and mitochondrial respiratory chain (MRC) enzyme activities by spectrophotometric methods. CoQ biosynthesis in fibroblasts was assayed by studying the incorporation of radiolabeled 4-hydroxy[U 14C] benzoic acid by HPLC with radiometric detection. RESULTS Mitochondrial respiratory chain enzyme analysis showed a decrease in complex I + III and complex II + III activities. CoQ concentration in muscle was decreased (56 nmol/g of protein: reference values: 157-488 nmol/g protein). A reduced incorporation of radiolabeled 4-hydroxy[U- 14C] benzoic acid was observed in the patient (19% of incorporation respect to the median control values). After 16 months of CoQ supplementation, the patient is now able to walk unaided and cerebellar signs have disappeared. CONCLUSIONS Cerebellar ataxia associated with CoQ deficiency in our case might be allocated in the transprenylation pathway or in the metabolic steps after condensation of 4-hydroxybenzoate and the prenyl side chain of CoQ. Clinical improvement after CoQ supplementation was remarkable, supporting the importance of an early diagnosis of this kind of disorders.

Vocal cord paresis and diaphragmatic dysfunction are severe and frequent symptoms of GDAP1-associated neuropathy

Cranial nerve involvement in Charcot-Marie-Tooth disease (CMT) is rare, though there are a number of CMT syndromes in which vocal cord paralysis is a characteristic feature. CMT disease due to mutations in the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) has been reported to be associated with vocal cord and diaphragmatic palsy. In order to address the prevalence of these complications in patients with GDAP1 mutations we evaluated vocal cord and respiratory function in nine patients from eight unrelated families with this disorder. Hoarseness of the voice and inability to speak loudly were reported by eight patients and one had associated symptoms of respiratory insufficiency. Patients were investigated by means of peripheral and phrenic nerve conduction studies, flexible laryngoscopy, pulmonary function studies and polysomnography. Nerve conduction velocities and pathological studies were compatible with axonal CMT (CMT2). Flexible laryngoscopy showed left vocal cord palsy in four cases, bilateral cord palsies in four cases and was normal in one case. Restrictive respiratory dysfunction was seen in the eight patients with vocal cord paresis who were all chair-bound. These eight had confirmed phrenic nerve dysfunction on neurophysiology evaluation. The patient with normal vocal cord and pulmonary function had a less severe clinical course.This study shows that CMT patients with GDAP1 mutations develop severe disability due to weakness of limb muscles and that laryngeal and respiratory muscle involvement occurs late in the disease process when significant proximal upper limb weakness has developed. The early and predominant involvement of the left vocal cord innervated by the longer left recurrent laryngeal nerve suggests a length dependent pattern of nerve degeneration. In GDAP1 neuropathy, respiratory function should be thoroughly investigated because life expectancy can be compromised due to respiratory failure.

Charcot-Marie-Tooth disease Genetic and clinical spectrum in a Spanish clinical series

Objectives: To determine the genetic distribution and the phenotypic correlation of an extensive series of patients with Charcot-Marie-Tooth disease in a geographically well-defined Mediterranean area. Methods: A thorough genetic screening, including most of the known genes involved in this disease, was performed and analyzed in this longitudinal descriptive study. Clinical data were analyzed and compared among the genetic subgroups. Results: Molecular diagnosis was accomplished in 365 of 438 patients (83.3%), with a higher success rate in demyelinating forms of the disease. The CMT1A duplication (PMP22 gene) was the most frequent genetic diagnosis (50.4%), followed by mutations in the GJB1 gene (15.3%), and in the GDAP1 gene (11.5%). Mutations in 13 other genes were identified, but were much less frequent. Sixteen novel mutations were detected and characterized phenotypically. Conclusions: The relatively high frequency of GDAP1 mutations, coupled with the scarceness of MFN2 mutations (1.1%) and the high proportion of recessive inheritance (11.6%) in this series exemplify the particularity of the genetic distribution of Charcot-Marie-Tooth disease in this region.

Phenotypical features of the p.R120W mutation in the GDAP1 gene causing autosomal dominant Charcot-Marie-Tooth disease

Mutations in the ganglioside‐induced‐differentiation‐associated protein 1 gene (GDAP1) can cause Charcot‐Marie‐Tooth (CMT) disease with demyelinating (CMT4A) or axonal forms (CMT2K and ARCMT2K). Most of these mutations present a recessive inheritance, but few autosomal dominant GDAP1 mutations have also been reported. We performed a GDAP1 gene screening in a clinically well‐characterized series of 81 index cases with axonal CMT neuropathy, identifying 17 patients belonging to 4 unrelated families in whom the heterozygous p.R120W was found to be the only disease‐causing mutation. The main objective was to fully characterize the neuropathy caused by this mutation. The clinical picture included a mild–moderate phenotype with onset around adolescence, but great variability. Consistently, ankle dorsiflexion and plantar flexion were impaired to a similar degree. Nerve conduction studies revealed an axonal neuropathy. Muscle magnetic resonance imaging studies demonstrated selective involvement of intrinsic foot muscles in all patients and a uniform pattern of fatty infiltration in the calf, with distal and superficial posterior predominance. Pathological abnormalities included depletion of myelinated fibers, regenerative clusters and features of axonal degeneration with mitochondrial aggregates. Our findings highlight the relevance of dominantly transmitted p.R120W GDAP1 gene mutations which can cause an axonal CMT with a wide clinical profile.

Missense mutations in the SH3TC2 protein causing Charcot-Marie-Tooth disease type 4C affect its localization in the plasma membrane and endocytic pathway.

Mutations in SH3TC2 (KIAA1985) cause Charcot-Marie-Tooth disease (CMT) type 4C, a demyelinating inherited neuropathy characterized by early-onset and scoliosis. Here we demonstrate that the SH3TC2 protein is present in several components of the endocytic pathway including early endosomes, late endosomes and clathrin-coated vesicles close to the trans-Golgi network and in the plasma membrane. Myristoylation of SH3TC2 in glycine 2 is necessary but not sufficient for the proper location of the protein in the cell membranes. In addition to myristoylation, correct anchoring also needs the presence of SH3 and TPR domains. Mutations that cause a stop codon and produce premature truncations that remove most of the TPR domains are expressed as the wild-type protein. In contrast, missense mutations in or around the region of the first-TPR domain are absent from early endosomes, reduced in plasma membrane and late endosomes and are variably present in clathrin-coated vesicles. Our findings suggest that the endocytic and membrane trafficking pathway is involved in the pathogenesis of CMT4C disease. We postulate that missense mutations of SH3TC2 could impair communication between the Schwann cell and the axon causing an abnormal myelin formation.

Coenzyme Q10‐responsive ataxia: 2‐year‐treatment follow‐up

We assessed the clinical outcome after coenzyme Q10 (CoQ10) therapy in 14 patients presenting ataxia classified into two groups according to CoQ10 values in muscle (deficient or not). We performed an open‐label prospective study: patients were evaluated clinically (international cooperative ataxia rating scale [ICARS] scale, MRI, and videotape registration) at baseline and every 6 months during a period of 2 years after CoQ10 treatment (30 mg/kg/day). Patients with CoQ10 deficiency showed a statistically significant reduction of ICARS scores (Wilcoxon test: P = 0.018) after 2 years of CoQ10 treatment when compared with baseline conditions. In patients without CoQ10 deficiency, no statistically significant differences were observed in total ICARS scores after therapy, although 1 patient from this group showed a remarkable clinical amelioration. Biochemical diagnosis of CoQ10 deficiency was a useful tool for the selection of patients who are good candidates for treatment as all of them responded to therapy. However, the remarkable clinical response in 1 case without CoQ10 deficiency highlights the importance of treatment trials for identification of patients with CoQ10‐responsive ataxia.

The p.R1109X mutation in SH3TC2 gene is predominant in Spanish Gypsies with Charcot-Marie-Tooth disease type 4

Charcot–Marie–Tooth (CMT) disease type 4 (CMT4) is the name given to autosomal recessive forms of hereditary motor and sensory neuropathy (HMSN). When we began this study, three genes or loci associated with inherited peripheral neuropathies had already been identified in the European Gypsy population: HMSN‐Lom (MIM 601455), HMSN‐Russe (MIM 605285) and the congenital cataracts facial dysmorphism neuropathy syndrome (MIM 604168). We have carried out genetic analyses in a series of 20 Spanish Gypsy families diagnosed with a demyelinating CMT disease compatible with an autosomal recessive trait. We found the p.R148X mutation in the N‐myc downstream‐regulated gene 1 gene to be responsible for the HMSN‐Lom in four families and also possible linkage to the HMSN‐Russe locus in three others. We have also studied the CMT4C locus because of the clinical similarities and showed that in 10 families, the disease is caused by mutations located on the SH3 domain and tetratricopeptide repeats 2 (SH3TC2) gene: p.R1109X in 20 out of 21 chromosomes and p.C737_P738delinsX in only one chromosome. Moreover, the SH3TC2 p.R1109X mutation is associated with a conserved haplotype and, therefore, may be a private founder mutation for the Gypsy population. Estimation of the allelic age revealed that the SH3TC2 p.R1109X mutation may have arisen about 225 years ago, probably as the consequence of a bottleneck.

Epidemiology of Usher Syndrome in Valencia and Spain

Objective: To obtain epidemiological data on the prevalence of the different types of Usher syndrome (US) in Spain, since these data were missing; to estimate the proportion of sporadic cases among simplex families, and calculate the prevalence of the Usher syndrome in a homogeneous population from Eastern Spain (3,875,234 inhabitants) that is representative of the Spanish population. Methods: Otological, ophthalmological and genetic studies were performed in 89 US patients from 46 families and subjected to statistical and segregation analysis. Results: 41.6% of them suffered US type I, 46.1% type II, and in 12.3% the classification remains unclear. The estimated prevalence for the Province of Valencia was 4.2/100,000. There was a notable excess of male-only affected multiplex sibships in our sample that could be attributable to an X-linked inheritance. Conclusions: The number of families with USI type was similar to that of families with USII type. The estimated prevalence for the Province of Valencia is in agreement with other reports in which the estimate for the prevalence of US ranges from 1.8 to 6.2/100,000.