The central nervous system phenotype of X-linked Charcot-Marie-Tooth disease: a transient disorder of children and young adults.

We describe 2 patients with X-linked Charcot-Marie-Tooth disease, type 1 (CMTX1) disease and central nervous system manifestations and review 19 cases from the literature. Our first case had not been previously diagnosed with Charcot-Marie-Tooth disease, and the second case, although known to have Charcot-Marie-Tooth disease, was suspected of having CMTX1 after presentation with central nervous system manifestations. The most common central nervous system manifestations were transient and included dysarthria, ataxia, hemiparesis, and tetraparesis resembling periodic paralysis. Of the 21 patients, 19 presented at 21 years of age or younger, implicating CMTX1 with transient central nervous system manifestations as a disorder that predominantly affects children and adolescents. CMTX1 should be included in the differential diagnosis of patients who present with transient central nervous system phenomena, including stroke-like episodes, tetraparesis suggestive of periodic paralysis, dysarthria, ataxia, or combinations of these deficits. Reversible, bilateral, nonenhancing white matter lesions and restricted diffusion on magnetic resonance imaging are characteristic features of the central nervous system phenotype of CMTX1.

Duplication within the SEPT9 gene associated with a founder effect in North American families with hereditary neuralgic amyotrophy.

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant disorder associated with recurrent episodes of focal neuropathy primarily affecting the brachial plexus. Point mutations in the SEPT9 gene have been previously identified as the molecular basis of HNA in some pedigrees. However in many families, including those from North America demonstrating a genetic founder haplotype, no sequence mutations have been detected. We report an intragenic 38 Kb SEPT9 duplication that is linked to HNA in 12 North American families that share the common founder haplotype. Analysis of the breakpoints showed that the duplication is identical in all pedigrees, and molecular analysis revealed that the duplication includes the 645 bp exon in which previous HNA mutations were found. The SEPT9 transcript variants that span this duplication contain two in-frame repeats of this exon, and immunoblotting demonstrates larger molecular weight SEPT9 protein isoforms. This exon also encodes for a majority of the SEPT9 N-terminal proline rich region suggesting that this region plays a role in the pathogenesis of HNA.

CC2D2A is mutated in Joubert syndrome and interacts with the ciliopathy-associated basal body protein CEP290.

Joubert syndrome and related disorders (JSRD) are primarily autosomal-recessive conditions characterized by hypotonia, ataxia, abnormal eye movements, and intellectual disability with a distinctive mid-hindbrain malformation. Variable features include retinal dystrophy, cystic kidney disease, and liver fibrosis. JSRD are included in the rapidly expanding group of disorders called ciliopathies, because all six gene products implicated in JSRD (NPHP1, AHI1, CEP290, RPGRIP1L, TMEM67, and ARL13B) function in the primary cilium/basal body organelle. By using homozygosity mapping in consanguineous families, we identify loss-of-function mutations in CC2D2A in JSRD patients with and without retinal, kidney, and liver disease. CC2D2A is expressed in all fetal and adult tissues tested. In ciliated cells, we observe localization of recombinant CC2D2A at the basal body and colocalization with CEP290, whose cognate gene is mutated in multiple hereditary ciliopathies. In addition, the proteins can physically interact in vitro, as shown by yeast two-hybrid and GST pull-down experiments. A nonsense mutation in the zebrafish CC2D2A ortholog (sentinel) results in pronephric cysts, a hallmark of ciliary dysfunction analogous to human cystic kidney disease. Knockdown of cep290 function in sentinel fish results in a synergistic pronephric cyst phenotype, revealing a genetic interaction between CC2D2A and CEP290 and implicating CC2D2A in cilium/basal body function. These observations extend the genetic spectrum of JSRD and provide a model system for studying extragenic modifiers in JSRD and other ciliopathies.

Charcot-Marie-Tooth disease.

The family of hereditary peripheral neuropathies that makes up Charcot-Marie-Tooth disease (CMT) comprises some of the most common neuromuscular disorders. Over the past decade, understanding of the molecular basis of CMT has increased enormously. In addition, the neurophysiologic deficits and clinical problems associated with CMT are more clearly delineated, and the precise genetic cause of many types of CMT has now been determined. Advances in molecular biology and genetic manipulation techniques have allowed the development of animal models of some of these CMT types, allowing more productive scientific exploration of possible treatments. Recent treatment advances that have been effective in animal models include oral supplementation with curcumin and vitamin C (ascorbic acid), and the use of onapristone, a progesterone antagonist. Human trials with vitamin C are currently in progress. While ongoing molecular genetic research continues to identify more of the mutant genes and proteins that cause the various disease subtypes, clinical research should continue to focus on developing pharmaceutical and rehabilitative therapies to ameliorate nerve degeneration and ultimately improve function for patients with CMT. These patients optimally should be managed in a comprehensive, multidisciplinary setting involving neurologists, physiatrists, orthopedic surgeons, physical and occupational therapists, and orthotists. Treatment should be aimed at maximizing independence and quality of life.

Joubert syndrome (and related disorders) (OMIM 213300).

Joubert syndrome (JS) and related disorders are characterized by the 'molar tooth sign' (cerebellar vermis hypoplasia and brainstem anomalies) on MRI, hypotonia, developmental delay, ataxia, irregular breathing pattern and abnormal eye movements. Combinations of additional features such as polydactyly, ocular coloboma, retinal dystrophy, renal disease, hepatic fibrosis, encephalocele, and other brain malformations define clinical sub-types. Recent identification of the NPHP1, AHI1, and CEP290 genes has started to reveal the molecular basis of JS, which may implicate the primary cilium in these disorders. Additional genes remain to be identified.

Inherited focal, episodic neuropathies: hereditary neuropathy with liability to pressure palsies and hereditary neuralgic amyotrophy.

Hereditary neuropathy with liability to pressure palsies (HNPP; also called tomaculous neuropathy) is an autosomal-dominant disorder that produces a painless episodic, recurrent, focal demyelinating neuropathy. HNPP generally develops during adolescence, and may cause attacks of numbness, muscular weakness, and atrophy. Peroneal palsies, carpal tunnel syndrome, and other entrapment neuropathies may be frequent manifestations of HNPP. Motor and sensory nerve conduction velocities may be reduced in clinically affected patients, as well as in asymptomatic gene carriers. The histopathological changes observed in peripheral nerves of HNPP patients include segmental demyelination and tomaculous or "sausage-like" formations. Mild overlap of clinical features with Charcot-Marie-Tooth (CMT) disease type 1 (CMT1) may lead patients with HNPP to be misdiagnosed as having CMT1. HNPP and CMT1 are both demyelinating neuropathies, however, their clinical, pathological, and electrophysiological features are quite distinct. HNPP is most frequently associated with a 1.4-Mb pair deletion on chromosome 17p12. A duplication of the identical region leads to CMT1A. Both HNPP and CMT1A result from a dosage effect of the PMP22 gene, which is contained within the deleted/duplicated region. This is reflected in reduced mRNA and protein levels in sural nerve biopsy samples from HNPP patients. Treatment for HNPP consists of preventative and symptom-easing measures. Hereditary neuralgic amyotrophy (HNA; also called familial brachial plexus neuropathy) is an autosomal-dominant disorder causing episodes of paralysis and muscle weakness initiated by severe pain. Individuals with HNA may suffer repeated episodes of intense pain, paralysis, and sensory disturbances in an affected limb. The onset of HNA is at birth or later in childhood with prognosis for recovery usually favorable; however, persons with HNA may have permanent residual neurological dysfunction following attack(s). Episodes are often triggered by infections, immunizations, the puerperium, and stress. Electrophysiological studies show normal or mildly prolonged motor nerve conduction velocities distal to the affected brachial plexus. Pathological studies have found axonal degeneration in nerves examined distal to the plexus abnormality. In some HNA pedigrees there are characteristic facial features, including hypotelorism. The prognosis for recovery of normal function of affected limbs in HNA is good, although recurrent episodes may cause residual deficits. HNA is genetically linked to chromosome 17q25, where mutations in the septin-9 (SEPT9) gene have been found.

Senataxin, the yeast Sen1p orthologue: characterization of a unique protein in which recessive mutations cause ataxia and dominant mutations cause motor neuron disease.

A severe recessive cerebellar ataxia, Ataxia-Oculomotor Apraxia 2 (AOA2) and a juvenile onset form of dominant amyotrophic lateral sclerosis (ALS4) result from mutations of the Senataxin (SETX) gene. To begin characterization this disease protein, we developed a specific antibody to the DNA/RNA helicase domain of SETX. In murine brain, SETX concentrates in several regions, including cerebellum, hippocampus and olfactory bulb with a general neuronal expression profile, colocalizing with NeuN. In cultured cells, we found that SETX was cytoplasmically diffuse, but in the nucleus, SETX was punctate, colocalizing with fibrillarin, a marker of the nucleolus. In differentiated non-cycling cells, nuclear SETX was not restricted to the nucleolus but was diffuse within the nucleoplasm, suggesting cell-cycle-dependent localization. SETX missense mutations cluster within the N-terminus and helicase domains. Flag tagging at the N-terminus caused protein mislocation to the nucleoplasm and failure to export to the cytoplasm, suggesting that the N-terminus may be essential for correct SETX localization. We report here the first characterization of SETX protein, which may provide future insights into a new mechanism leading to neuron death.

Mutations in SEPT9 cause hereditary neuralgic amyotrophy.

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant recurrent neuropathy affecting the brachial plexus. HNA is triggered by environmental factors such as infection or parturition. We report three mutations in the gene septin 9 (SEPT9) in six families with HNA linked to chromosome 17q25. HNA is the first monogenetic disease caused by mutations in a gene of the septin family. Septins are implicated in formation of the cytoskeleton, cell division and tumorigenesis.

SIMPLE interacts with NEDD4 and TSG101: evidence for a role in lysosomal sorting and implications for Charcot-Marie-Tooth disease.

Mutation of the SIMPLE gene (small integral membrane protein of the lysosome/late endosome) is the molecular basis of Charcot-Marie-Tooth disease type 1C (CMT1C), a demyelinating peripheral neuropathy. Although the precise function of SIMPLE is unknown, prior reports suggest it localizes to the lysosome/late endosome. Furthermore, murine Simple interacts with Nedd4 (neural precursor cell expressed, developmentally downregulated 4), an E3 ubiquitin ligase that is important for regulating lysosomal degradation of plasma membrane proteins. To bring insights into the biochemical function of human SIMPLE, we confirmed that human SIMPLE interacts with NEDD4 and also report a novel interaction with tumor susceptibility gene 101 (TSG101), a class E vacuolar sorting protein. TSG101 is known to function downstream of NEDD4, sorting ubiquitinated substrates into multivesicular bodies (MVBs), which then deliver their cargo into the lysosomal lumen for degradation. Given the interaction with NEDD4 and TSG101, and the localization of SIMPLE along the lysosomal degradation pathway, we hypothesize that SIMPLE plays a role in the lysosomal sorting of plasma membrane proteins. We examine three CMT1C-associated SIMPLE mutations and show that they do not affect the interaction with NEDD4 or TSG101, nor do they lead to altered subcellular localization.

Prenatal diagnosis in pregnancies at risk for Joubert syndrome by ultrasound and MRI.

OBJECTIVES: To describe the prenatal imaging findings in fetuses at risk for Joubert syndrome (JS), review the literature and propose a protocol for prenatal diagnosis of JS using ultrasound and MRI. METHODS: We reviewed prenatal ultrasound and fetal MRI studies in two pregnancies at 25% recurrence risk for JS and correlated these findings with gross neuropathology in one affected fetus. RESULTS: While abnormalities such as occipital encephalocele or enlarged cisterna magna have been identified before mid-trimester, the definitive diagnosis of JS, based on core cerebellar findings, has only been possible after 17 weeks' gestation. CONCLUSIONS: With longitudinal monitoring, it is possible to diagnose JS in at-risk pregnancies before 24 weeks' gestation. On the basis of our data and review of the literature, we propose a protocol for monitoring pregnancies at risk for JS, utilizing serial ultrasounds combined with fetal MRI at 20-22 weeks' gestation to maximize the accuracy of prenatal diagnosis.

The NPHP1 gene deletion associated with juvenile nephronophthisis is present in a subset of individuals with Joubert syndrome.

Joubert syndrome (JS) is an autosomal recessive multisystem disease characterized by cerebellar vermis hypoplasia with prominent superior cerebellar peduncles (the "molar tooth sign" [MTS] on axial magnetic resonance imaging), mental retardation, hypotonia, irregular breathing pattern, and eye-movement abnormalities. Some individuals with JS have retinal dystrophy and/or progressive renal failure characterized by nephronophthisis (NPHP). Thus far, no mutations in the known NPHP genes, particularly the homozygous deletion of NPHP1 at 2q13, have been identified in subjects with JS. A cohort of 25 subjects with JS and either renal and/or retinal complications and 2 subjects with only juvenile NPHP were screened for mutations in the NPHP1 gene by standard methods. Two siblings affected with a mild form of JS were found to have a homozygous deletion of the NPHP1 gene identical, by mapping, to that in subjects with NPHP alone. A control subject with NPHP and with a homozygous NPHP1 deletion was also identified, retrospectively, as having a mild MTS and borderline intelligence. The NPHP1 deletion represents the first molecular defect associated with JS in a subset of mildly affected subjects. Cerebellar malformations consistent with the MTS may be relatively common in patients with juvenile NPHP without classic symptoms of JS.

SIMPLE mutation in demyelinating neuropathy and distribution in sciatic nerve.

Charcot-Marie-Tooth neuropathy type 1C (CMT1C) is an autosomal dominant demyelinating peripheral neuropathy caused by missense mutations in the small integral membrane protein of lysosome/late endosome (SIMPLE) gene. To investigate the prevalence of SIMPLE mutations, we screened a cohort of 152 probands with various types of demyelinating or axonal and pure motor or sensory inherited neuropathies. SIMPLE mutations were found only in CMT1 patients, including one G112S and one W116G missense mutations. A novel I74I polymorphism was identified, yet no splicing defect of SIMPLE is likely. Haplotype analysis of STR markers and intragenic SNPs linked to the gene demonstrated that families with the same mutation are unlikely to be related. The clustering of the G112S, T115N, and W116G mutations within five amino acids suggests this domain may be critical to peripheral nerve myelination. Electrophysiological studies showed that CMT1C patients from six pedigrees (n = 38) had reduced nerve conduction velocities ranging from 7.5 to 27.0m/sec (peroneal). Two patients had temporal dispersion of nerve conduction and irregularity of conduction slowing, which is unusual for CMT1 patients. We report the expression of SIMPLE in various cell types of the sciatic nerve, including Schwann cells, the affected cell type in CMT1C.

Cerebral and cerebellar motor activation abnormalities in a subject with Joubert syndrome: functional magnetic resonance imaging (MRI) study.

Joubert syndrome is an autosomal recessive disorder characterized by hypotonia, ataxia, developmental delay, and a distinctive hindbrain malformation involving the cerebellum and brain stem, visualized radiographically on magnetic resonance imaging (MRI) as the "molar tooth sign." In postmortem brains from subjects with Joubert syndrome, there is an apparent absence of decussation of both corticospinal and superior cerebellar tracts, although the functional significance has not been elucidated. We sought to explore the cerebral and cerebellar activation pattern elicited by finger tapping in an adolescent with Joubert syndrome and in a normal control subject using functional MRI. In contrast to the typical highly lateralized activation seen in our control subject, the subject with Joubert syndrome demonstrated striking bilateral activation of the sensorimotor and cerebellar cortex. Although our functional MRI data do not indicate a clear absence of decussation, the abnormal activation pattern observed suggests altered brain functional organization in relation to anatomic differences. Malformation of the hindbrain could result in recruitment of alternative pathways, similar to what has been observed following ischemic injury to the developing or mature central nervous system.

Charcot-Marie-Tooth disease: electrophysiology, molecular genetics and clinical management.

Over the past decade there has been a huge increase in the understanding of the molecular basis of Charcot-Marie-Tooth disease (CMT). Additionally there has been a better delineation of the neurophysiological deficits and clinical problems associated with CMT. This paper reviews the current molecular basis of CMT and the electrophysiological, clinical and phenotypical characteristics of the various subtypes, followed by a discussion of novel and promising therapeutic interventions that potentially could be used as part of a treatment regimen for CMT. These interventions may involve attempts to slow down or stop neurodegenerative processes through nerve growth factors, limiting oxidative stress by using antioxidants, or normalizing gene expression through genetic manipulation. Other potential therapeutic target areas include the progesterone receptor on myelin-forming Schwann cells, the immune system via modulation of nerve inflammation, and enhancing glutathione transferase activity. While ongoing molecular research continues to identify more of the mutant genes and proteins that cause the various disease subtypes, the focus of clinical research should continue to be on developing pharmaceutical and rehabilitative therapies to reverse nerve degeneration and ultimately improve the functioning of people with CMT.

DNA/RNA helicase gene mutations in a form of juvenile amyotrophic lateral sclerosis (ALS4).

Juvenile amyotrophic lateral sclerosis (ALS4) is a rare autosomal dominant form of juvenile amyotrophic lateral sclerosis (ALS) characterized by distal muscle weakness and atrophy, normal sensation, and pyramidal signs. Individuals affected with ALS4 usually have an onset of symptoms at age <25 years, a slow rate of progression, and a normal life span. The ALS4 locus maps to a 1.7-Mb interval on chromosome 9q34 flanked by D9S64 and D9S1198. To identify the molecular basis of ALS4, we tested 19 genes within the ALS4 interval and detected missense mutations (T3I, L389S, and R2136H) in the Senataxin gene (SETX). The SETX gene encodes a novel 302.8-kD protein. Although its function remains unknown, SETX contains a DNA/RNA helicase domain with strong homology to human RENT1 and IGHMBP2, two genes encoding proteins known to have roles in RNA processing. These observations of ALS4 suggest that mutations in SETX may cause neuronal degeneration through dysfunction of the helicase activity or other steps in RNA processing.

Genomic organization and mutation analysis of three candidate genes for hereditary neuralgic amyotrophy.

Hereditary neuralgic amyotrophy (HNA) is an autosomal-dominant inherited recurrent focal neuropathy affecting mainly the brachial plexus. In this study we report the genomic structure and mutation analysis of three candidate genes: sphingosine kinase 1 (SPHK1); tissue inhibitor of metalloproteinase 2 (TIMP2); and cytoglobin (CYGB). We did not find any disease-associated mutations, indicating that HNA is not caused by point mutations in these genes. However, we identified several sequencing errors in the cDNA of SPHK1 as well as seven novel single-nucleotide polymorphisms.

Joubert syndrome: a haplotype segregation strategy and exclusion of the zinc finger protein of cerebellum 1 (ZIC1) gene.

Joubert syndrome (JS) is a rare autosomal recessive malformation syndrome, involving dysgenesis of the cerebellar vermis with accompanying brainstem malformations (comprising the molar tooth sign). JS is characterized by hypotonia, developmental delay, intermittent hyperpnea and apnea, and abnormal eye movements. A single locus for JS was previously identified on 9q34 in a consanguineous family of Arabian origin. However, linkage to this locus has subsequently been shown to be rare. We have ascertained 35 JS pedigrees for haplotype segregation analysis of genetic loci for genes with a putative role in cerebellar development. We examined the ZIC1 gene as a functional candidate for JS as Zic1(-/-) null mice have a phenotype reminiscent of JS. We undertook mutational analysis of ZIC1 by standard mutational analysis (dideoxy-fingerprinting (ddf)) of 47 JS probands, and fully sequenced the coding region in five of these probands. By these means, ZIC1 was excluded from playing a causal role in most cases of JS as no disease-associated mutations were identified. Further, linkage to the ZIC1 genetic locus (3q24) was excluded in 21 of 35 pedigrees by haplotype segregation analysis of closely spaced markers. The remaining 14 of 35 pedigrees were consistent with linkage. However, this number does not significantly depart from that expected by random chance (16.5) for this cohort. Therefore, this systematic approach has been validated as a means to prioritize functional candidate genes and enables us to confine mutational analysis to only those probands whose segregation is consistent with linkage to any given locus.

Molar tooth sign of the midbrain-hindbrain junction: occurrence in multiple distinct syndromes.

The Molar Tooth Sign (MTS) is defined by an abnormally deep interpeduncular fossa; elongated, thick, and mal-oriented superior cerebellar peduncles; and absent or hypoplastic cerebellar vermis that together give the appearance of a "molar tooth" on axial brain MRI through the junction of the midbrain and hindbrain (isthmus region). It was first described in Joubert syndrome (JS) where it is present in the vast majority of patients with this diagnosis. We previously showed that the MTS is a component of several other syndromes, including Dekaban-Arima (DAS), Senior-Löken, and COACH (cerebellar vermis hypoplasia (CVH), oligophrenia, ataxia, coloboma, and hepatic fibrosis). Here we present evidence that the MTS is seen together with polymicrogyria, Váradi-Papp syndrome (Orofaciodigital VI (OFD VI)), and a new syndrome with encephalocele and cortical renal cysts. We also present a new patient with COACH syndrome plus the MTS. We propose that the MTS is found in multiple distinct clinical syndromes that may share common developmental mechanisms. Proper classification of patients with these variants of the MTS will be essential for localization and identification of mutant genes.