Familial opticoacoustic nerve degeneration and polyneuropathy

Characterizing microRNA editing and mutation sites in Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder whose pathogenesis is still unclear. MicroRNAs (miRNAs) are a kind of endogenous small non-coding RNAs that play important roles in the post-transcriptional regulation of genes. Recent researches show that miRNAs are edited in multiple ways especially in central nervous systems. A-to-I editing of RNA catalyzed by Adenosine deaminases acting on RNA (ADARs) happens intensively in brain and is also noticed in other organs and tissues. Although miRNAs are widely edited in human brain, miRNA editing in ASD is still largely unexplored. In order to reveal the editing events of miRNAs in ASD, we analyzed 131 miRNA-seq samples from 8 different brain regions of ASD patients and normal controls. We identified 834 editing sites with significant editing levels, of which 70 sites showed significantly different editing levels in the superior frontal gyrus samples of ASD patients (ASD-SFG) when compared with those of control samples. The editing level of an A-to-I editing site in hsa-mir-376a-1 (hsa-mir-376a-1_9_A_g) in ASD-SFG is higher than that of normal controls, and the difference is exaggerated in individuals under 10 years. The increased expression of ADAR1 is consistent with the increased editing level of hsa-mir-376a-1_9_A_g in ASD-SFG samples compared to normal SFG samples. Furthermore, we verify that A-to-I edited hsa-mir-376a-5p directly represses GPR85 and NAPB, which may contribute to the abnormal neuronal development of ASD patients. These results provide new insights into the mechanism of ASD.

Zebrafish Model for Nonsyndromic X-Linked Sensorineural Deafness, DFNX1

Hereditary deafness is often a neurosensory disorder and affects the quality of life of humans. Only three X-linked genes (POU class 3 homeobox 4 (POU3F4), phosphoribosyl pyrophosphate synthetase 1 (PRPS1), and small muscle protein X-linked (SMPX)) are known to be involved in nonsyndromic hearing loss. Four PRPS1 missense mutations have been found to associate with X-linked nonsyndromic sensorineural deafness (DFNX1/DFN2) in humans. However, a causative relationship between PRPS1 mutations and hearing loss in humans has not been well studied in any animal model. Phosphoribosyl pyrophosphate synthetase 1 (PRS-I) is highly conserved in vertebrate taxa. In this study, we used the zebrafish as a model to investigate the auditory role of zebrafish orthologs (prps1a and prps1b) of the human PRPS1 gene with whole mount in situ hybridization, reverse transcription polymerase chain reaction, phenotypic screening, confocal imaging, and electrophysiological methods. We found that both prps1a and prps1b genes were expressed in the inner ear of zebrafish. Splice-blocking antisense morpholino oligonucleotides (MO1 and MO2) caused exon-2 skip and intron-2 retention of prps1a and exon-2 skip and intron-1 retention of prps1b to knock down functions of the genes, respectively. MO1 and MO2 morphants had smaller otic vesicles and otoliths, fewer inner ear hair cells, and lower microphonic response amplitude and sensitivity than control zebrafish. Therefore, knockdown of either prps1a or prps1b resulted in significant sensorineural hearing loss in zebrafish. We conclude that the prps1 genes are essential for hearing in zebrafish, which has the potential to help us understand the biology of human deafness DFNX1/DFN2. Anat Rec, 303:544-555, 2020. © 2019 American Association for Anatomy.

Expanding the phenotype of PRPS1 syndromes in females: neuropathy, hearing loss and retinopathy

Background

Phosphoribosyl pyrophosphate synthetase (PRS) I deficiency is a rare medical condition caused by missense mutations in PRPS1 that lead to three different phenotypes: Arts Syndrome (MIM 301835), X-linked Charcot-Marie-Tooth (CMTX5, MIM 311070) or X-linked non-syndromic sensorineural deafness (DFN2, MIM 304500). All three are X-linked recessively inherited and males affected display variable degree of central and peripheral neuropathy. We applied whole exome sequencing to a three-generation family with optic atrophy followed by retinitis pigmentosa (RP) in all three cases, and ataxia, progressive peripheral neuropathy and hearing loss with variable presentation.

Methods

Whole exome sequencing was performed in two affecteds and one unaffected member of the family. Sanger sequencing was used to validate and segregate the 12 candidate mutations in the family and to confirm the absence of the novel variant in PRPS1 in 191 controls. The pathogenic role of the novel mutation in PRPS1 was assessed in silico and confirmed by enzymatic determination of PRS activity, mRNA expression and sequencing, and X-chromosome inactivation.

Results

A novel missense mutation was identified in PRPS1 in the affected females. Age of onset, presentation and severity of the phenotype are highly variable in the family: both the proband and her mother have neurological and ophthalmological symptoms, whereas the phenotype of the affected sister is milder and currently confined to the eye. Moreover, only the proband displayed a complete lack of expression of the wild type allele in leukocytes that seems to correlate with the degree of PRS deficiency and the severity of the phenotype. Interestingly, optic atrophy and RP are the only common manifestations to all three females and the only phenotype correlating with the degree of enzyme deficiency.

Conclusions

These results are in line with recent evidence of the existence of intermediate phenotypes in PRS-I deficiency syndromes and demonstrate that females can exhibit a disease phenotype as severe and complex as their male counterparts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-014-0190-9) contains supplementary material, which is available to authorized users.

Inborn errors of purine metabolism: clinical update and therapies

Inborn errors of purine metabolism exhibit broad neurological, immunological, haematological and renal manifestations. Limited awareness of the phenotypic spectrum, the recent descriptions of newer disorders and considerable genetic heterogeneity, have contributed to long diagnostic odysseys for affected individuals. These enzymes are widely but not ubiquitously distributed in human tissues and are crucial for synthesis of essential nucleotides, such as ATP, which form the basis of DNA and RNA, oxidative phosphorylation, signal transduction and a range of molecular synthetic processes. Depletion of nucleotides or accumulation of toxic intermediates contributes to the pathogenesis of these disorders. Maintenance of cellular nucleotides depends on the three aspects of metabolism of purines (and related pyrimidines): de novo synthesis, catabolism and recycling of these metabolites. At present, treatments for the clinically significant defects of the purine pathway are restricted: purine 5'-nucleotidase deficiency with uridine; familial juvenile hyperuricaemic nephropathy (FJHN), adenine phosphoribosyl transferase (APRT) deficiency, hypoxanthine phosphoribosyl transferase (HPRT) deficiency and phosphoribosyl-pyrophosphate synthetase superactivity (PRPS) with allopurinol; adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiencies have been treated by bone marrow transplantation (BMT), and ADA deficiency with enzyme replacement with polyethylene glycol (PEG)-ADA, or erythrocyte-encapsulated ADA; myeloadenylate deaminase (MADA) and adenylosuccinate lyase (ADSL) deficiencies have had trials of oral ribose; PRPS, HPRT and adenosine kinase (ADK) deficiencies with S-adenosylmethionine; and molybdenum cofactor deficiency of complementation group A (MOCODA) with cyclic pyranopterin monophosphate (cPMP). In this review we describe the known inborn errors of purine metabolism, their phenotypic presentations, established diagnostic methodology and recognised treatment options.

Hereditäre Optikusatrophien

Bei hereditären Optikusatrophien werden 2 Untergruppen differenziert: isolierte hereditäre Optikusatrophien und hereditäre Optikusatrophien als Teil von syndromalen Erkrankungen. In der 1. Gruppe ist die Beeinträchtigung des N. opticus typischerweise die einzige Manifestation. Diese Gruppe umfasst insbesondere autosomal-dominante und autosomal-rezessive Optikusatrophien, darüber hinaus auch die mitochondrial vererbte hereditäre Leber-Optikusneuropathie (LHON).

In der 2. Gruppe, die die syndromalen Erkrankungen umfasst, wird eine Vielzahl neurologischer und anderer systemischer Auffälligkeiten beobachtet. Am häufigsten sind hier Veränderungen der mitochondrialen DNA (mtDNA) ursächlich. Weiterhin ist eine Optikusatrophie Symptom von einigen erblichen peripheren Neuropathien bzw. Charcot-Marie-Tooth-Erkrankungen (CMT2A2, CMTX5), hereditären sensorischen Neuropathie Typ 3 (HSAN3), Friedreich-Ataxie, Leukodystrophien, Sphingolipidosen, Zeroidlipofuszinosen und Eisenspeichererkrankungen („neurodegeneration with brain iron accumulation“, NBIA). Im vorliegenden Beitrag werden die zugrundeliegenden genetischen Prädispositionen und die klinischen Phänotypen erläutert.

Exome Sequencing Reveals a Novel PRPS1 Mutation in a Family with CMTX5 without Optic Atrophy

Background

X-linked Charcot-Marie-Tooth disease type 5 (CMTX5) is caused by mutations in the gene encoding phosphoribosyl pyrophosphate synthetase I (PRPS1). There has been only one case report of CMTX5 patients. The aim of this study was to identify the causative gene in a family with CMTX with peripheral neuropathy and deafness.

Case Report

A Korean family with X-linked recessive CMT was enrolled. The age at the onset of hearing loss of the male proband was 5 months, and that of steppage gait was 6 years; he underwent cochlear surgery at the age of 12 years. In contrast to what was reported for the first patients with CMTX5, this patient did not exhibit optic atrophy. Furthermore, there was no cognitive impairment, respiratory dysfunction, or visual disturbance. Assessment of his family history revealed two male relatives with very similar clinical manifestations. Electrophysiological evaluations disclosed sensorineural hearing loss and peripheral neuropathy. Whole-exome sequencing identified a novel p.Ala121Gly (c.362C>G) PRPS1 mutation as the underlying genetic cause of the clinical phenotype.

Conclusions

A novel mutation of PRPS1 was identified in a CMTX5 family in which the proband had a phenotype of peripheral neuropathy with early-onset hearing loss, but no optic atrophy. The findings of this study will expand the clinical spectrum of X-linked recessive CMT and will be useful for the molecular diagnosis of clinically heterogeneous peripheral neuropathies.

Genetic and phenotypic variability of optic neuropathies

Hereditary optic neuropathies comprise a group of clinically and genetically heterogeneous disorders. Two subgroups can be formed: isolated hereditary optic atrophies and optic neuropathy as part of complex disorders. In group 1 of hereditary optic neuropathies, optic nerve dysfunction is typically the only manifestation of the disease. This group comprises autosomal dominant, autosomal recessive and X-linked recessive optic atrophy and the maternally inherited Leber's hereditary optic neuropathy. Among the autosomal-dominant forms of optic atrophy, Kjer's disease is most frequently observed. In the second group of complex disorders, various neurologic and other systemic abnormalities are regularly observed. Most frequent in this group are mtDNA mutations, inherited peripheral neuropathies, Charcot-Marie-Tooth disorders (CMT2A2, CMTX5), hereditary sensory neuropathy type 3 (HSAN3), Friedreich's ataxia, leukodystrophies, sphingolipidoses, ceroid-lipofuscinoses and neurodegeneration with brain iron accumulation. We review current knowledge about the underlying genetic predispositions, the most urgent open questions and how this may affect our management of this heterogeneous group of disorders in the future.

Hearing loss and PRPS1 mutations: Wide spectrum of phenotypes and potential therapy

OBJECTIVE

The purpose of this review was to evaluate the current literature on phosphoribosylpyrophosphate synthetase 1 (PRPS1)-related diseases and their consequences on hearing function.

DESIGN

A literature search of peer-reviewed, published journal articles was conducted in online bibliographic databases.

STUDY SAMPLE

Three databases for medical research were included in this review.

RESULTS

Mutations in PRPS1 are associated with a spectrum of non-syndromic to syndromic hearing loss. Hearing loss in male patients with PRPS1 mutations is bilateral, moderate to profound, and can be prelingual or postlingual, progressive or non-progressive. Audiogram shapes associated with PRPS1 deafness are usually residual and flat. Female carriers can have unilateral or bilateral hearing impairment. Gain of function mutations in PRPS1 cause a superactivity of the PRS-I protein whereas the loss-of-function mutations result in X-linked nonsyndromic sensorineural deafness type 2 (DFN2), or in syndromic deafness including Arts syndrome and X-linked Charcot-Marie-Tooth disease-5 (CMTX5).

CONCLUSIONS

Lower residual activity in PRS-I leads to a more severe clinical manifestation. Clinical and molecular findings suggest that the four PRPS1 disorders discovered to date belong to the same disease spectrum. Dietary supplementation with S-adenosylmethionine (SAM) appeared to alleviate the symptoms of Arts syndrome patients, suggesting that SAM could compensate for PRS-I deficiency.

Hereditary peripheral neuropathies of childhood: an overview for clinicians

This review focuses on the "pure" hereditary peripheral neuropathies where peripheral nerve disease is the main manifestation and does not address neurodegenerative disorders associated with but not dominated by peripheral neuropathy. Aetiologies of childhood-onset peripheral neuropathies differ from those of adult-onset, with more inherited conditions, especially autosomal recessive. Charcot-Marie-Tooth disease is the commonest neuromuscular disorder. The genetic labels of CMT (Charcot-Marie-Tooth) disease types 1-4 are the preferred sub-type terms. Clinical presentations and molecular genetic heterogeneity of hereditary peripheral neuropathies are diverse. For most patients worldwide, diagnostic studies are limited to clinical assessment. Such markers which could be used to identify specific sub-types include presentation in early childhood, scoliosis, marked sensory involvement, respiratory compromise, upper limb involvement, visual or hearing impairment, pyramidal signs and mental retardation. These key markers may assist targeted genetic testing and aid in diagnosing children where DNA testing is not possible.

PRPS1 mutations: four distinct syndromes and potential treatment

Phosphoribosylpyrophosphate synthetases (PRSs) catalyze the first step of nucleotide synthesis. Nucleotides are central to cell function, being the building blocks of nucleic acids and serving as cofactors in cellular signaling and metabolism. With this in mind, it is remarkable that mutations in phosphoribosylpyrophosphate synthetase 1 (PRPS1), which is the most ubiquitously expressed gene of the three PRS genes, are compatible with life. Mutations described thus far in PRPS1 are all missense mutations that result in PRS-I superactivity or in variable levels of decreased activity, resulting in X-linked Charcot-Marie-Tooth disease-5 (CMTX5), Arts syndrome, and X-linked nonsyndromic sensorineural deafness (DFN2). Patients with PRS-I superactivity primarily present with uric acid overproduction, mental retardation, ataxia, hypotonia, and hearing impairment. Postlingual progressive hearing loss is found as an isolated feature in DFN2 patients. Patients with CMTX5 and Arts syndrome have peripheral neuropathy, including hearing impairment and optic atrophy. However, patients with Arts syndrome are more severely affected because they also have central neuropathy and an impaired immune system. The neurological phenotype in all four PRPS1-related disorders seems to result primarily from reduced levels of GTP and possibly other purine nucleotides including ATP, suggesting that these disorders belong to the same disease spectrum. Preliminary results of S-adenosylmethionine (SAM) supplementation in two Arts syndrome patients show improvement of their condition, indicating that SAM supplementation in the diet could alleviate some of the symptoms of patients with PRPS1 spectrum diseases by replenishing purine nucleotides (J.C., unpublished data).

Optic atrophy and sensorineural hearing loss in a family caused by an R445H OPA1 mutation

Autosomal dominant optic atrophy (ADOA) is the most common form of inherited optic atrophy. Four genetic loci have been associated with ADOA: OPA1, OPA2, OPA3, and OPA4. Out of these four loci, only one gene has been identified, OPA1. We previously described a unique syndrome of optic atrophy, sensorineural hearing loss, ptosis, and ophthalmoplegia in two unrelated families associated with an R445H mutation in OPA1. The R445H mutation is the only OPA1 mutation that has been associated with this syndrome. In this manuscript, we clinically characterize an unrelated family with four members affected by optic atrophy and hearing loss without extraocular motility abnormalities or ptosis. This family also harbors the R445H mutation. These cases help illustrate the intra- and inter-family variability in phenotype associated with this mutation. As we continue to learn more about OPA1 and the function of its protein product, we will begin to understand the pathophysiology of optic atrophy. This understanding will ultimately lead to novel treatments directed toward preventing the visual loss and disability associated with this inherited disease.

Charcot-Marie-Tooth disease: a clinico-genetic confrontation

Charcot-Marie-Tooth disease (CMT) is the most common neuromuscular disorder. It represents a group of clinically and genetically heterogeneous inherited neuropathies. Here, we review the results of molecular genetic investigations and the clinical and neurophysiological features of the different CMT subtypes. The products of genes associated with CMT phenotypes are important for the neuronal structure maintenance, axonal transport, nerve signal transduction and functions related to the cellular integrity. Identifying the molecular basis of CMT and studying the relevant genes and their functions is important to understand the pathophysiological mechanisms of these neurodegenerative disorders, and the processes involved in the normal development and function of the peripheral nervous system. The results of molecular genetic investigations have impact on the appropriate diagnosis, genetic counselling and possible new therapeutic options for CMT patients.

Mutations in PRPS1, which encodes the phosphoribosyl pyrophosphate synthetase enzyme critical for nucleotide biosynthesis, cause hereditary peripheral neuropathy with hearing loss and optic neuropathy (cmtx5)

We have identified missense mutations at conserved amino acids in the PRPS1 gene on Xq22.3 in two families with a syndromic form of inherited peripheral neuropathy, one of Asian and one of European descent. The disease is inherited in an X-linked recessive manner, and the affected male patients invariably develop sensorineural hearing loss of prelingual type followed by gating disturbance and visual loss. The family of European descent was reported in 1967 as having Rosenberg-Chutorian syndrome, and recently a Korean family with the same symptom triad was identified with a novel disease locus CMTX5 on the chromosome band Xq21.32-q24. PRPS1 (phosphoribosyl pyrophosphate synthetase 1) is an isoform of the PRPS gene family and is ubiquitously expressed in human tissues, including cochlea. The enzyme mediates the biochemical step critical for purine metabolism and nucleotide biosynthesis. The mutations identified were E43D, in patients with Rosenberg-Chutorian syndrome, and M115T, in the Korean patients with CMTX5. We also showed decreased enzyme activity in patients with M115T. PRPS1 is the first CMT gene that encodes a metabolic enzyme, shedding a new light on the understanding of peripheral nerve-specific metabolism and also suggesting the potential of PRPS1 as a target for drugs in prevention and treatment of peripheral neuropathy by antimetabolite therapy.

A family with X-linked optic atrophy linked to the OPA2 locus Xp11.4-Xp11.2

Autosomal dominant optic atrophy (ADOA) is the most common inherited optic atrophy. Clinical features of ADOA include a slowly progressive bilateral loss of visual acuity, constriction of peripheral visual fields, central scotomas, and color vision abnormalities. Although ADOA is the most commonly inherited optic atrophy, autosomal recessive, X-linked, mitochondrial, and sporadic forms have also been reported. Four families with X-linked optic atrophy (XLOA) were previously described. One family was subsequently linked to Xp11.4-Xp11.2 (OPA2). This investigation studied one multi-generation family with an apparently X-linked form of optic atrophy and compared their clinical characteristics with those of the previously described families, and determined whether this family was linked to the same genetic locus. Fifteen individuals in a three-generation Idaho family underwent complete eye examination, color vision testing, automated perimetry, and fundus photography. Polymorphic markers were used to genotype each individual and to determine linkage. Visual acuities ranged from 20/30 to 20/100. All affected subjects had significant optic nerve pallor. Obligate female carriers were clinically unaffected. Preliminary linkage analysis (LOD score = 1.8) revealed that the disease gene localized to the OPA2 locus on Xp11.4-Xp11.2. Four forms of inherited optic neuropathy, ADOA, autosomal recessive optic atrophy (Costeff Syndrome), Leber hereditary optic neuropathy, and Charcot-Marie-Tooth disease with optic atrophy, are associated with mitochondrial dysfunction. Future identification of the XLOA gene will reveal whether this form of optic atrophy is also associated with a mitochondrial defect. Identification of the XLOA gene will advance our understanding of the inherited optic neuropathies and perhaps suggest treatments for these diseases. An improved understanding of inherited optic neuropathies may in turn advance our understanding of acquired optic nerve diseases, such as glaucoma and ischemic optic neuropathy.

Hereditary motor and sensory neuropathy type VI with optic atrophy

PURPOSE

To present the detailed clinical findings of a large family with hereditary motor and sensory neuropathy type VI (HMSN VI), a syndrome featuring optic atrophy.

DESIGN

Observational case series.

METHODS

A detailed history was obtained and physical examination was made of the extended family of the proband for evidence of neurologic dysfunction. The OPA1 gene was screened for mutations by direct DNA sequencing.

RESULTS

Twelve of 97 family members examined are affected with signs of HMSN VI. Three other members have either optic atrophy or peripheral neuropathy, thus allowing an appreciation of the full clinical spectrum of disease. No mutations were found in the OPA1 gene.

CONCLUSIONS

This family demonstrates the variable expressivity of this disorder as well as incomplete penetrance. This is the largest known family with HMSN VI. No association was found with changes in the OPA1 gene.

"Auditory neuropathy": physiologic and pathologic evidence calls for more diagnostic specificity

The term "auditory neuropathy" is being used in a rapidly increasing number of papers in the audiology/otolaryngology literature for a variety of individuals (mostly children) who fulfill the following criteria: (1) understanding of speech worse than predicted from the degree of hearing loss on their behavioral audiograms; (2) recordable otoacoustic emissions and/or cochlear microphonic; together with (3) absent or atypical auditory brain stem responses. Because of the general lack of anatomic foundation for the label "auditory neuropathy" as currently used, we review the anatomy of the auditory pathway, the definition of neuropathy and its demyelinating, axonal, and mixed variants. We submit that the diagnostic term "auditory neuropathy" is anatomically inappropriate unless patients have documented evidence for selective involvement of either the spiral ganglion cells or their axons, or of the 8th nerve as a whole. In view of biologic differences between peripheral nerves and white matter tracts in the brain, the term "auditory neuropathy" is inappropriate for pathologies affecting the central auditory pathway in the brainstem and brain selectively. Published reports of patients with "auditory neuropathy" indicate that they are extremely heterogeneous in underlying medical diagnosis, age, severity, test results, and that only a small number have undergone the detailed investigations that would enable a more precise diagnosis of the locus of their pathologies. The electrophysiology of peripheral neuropathies and the deficits expected with pathologies affecting the hair cells, spiral ganglion cells and their axons (auditory neuropathy sensu stricto), and brain stem relays are reviewed. In order to serve patients adequately, including potential candidates for cochlear implants, and to increase knowledge of auditory pathologies, we make a plea for more comprehensive evaluation of patients who fulfill the currently used audiologic criteria for "auditory neuropathy" in an effort to pinpoint the site of their pathologies. We suggest that the term auditory neuropathy be limited to cases in which the locus of pathology is limited to the spiral ganglion cells, their processes, or the 8th nerve, and that the term neural hearing loss be considered for pathologies that affect all higher levels of the auditory pathway, from the brainstem to the auditory cortex.

Charcot-Marie-Tooth disease (CMT): distinctive phenotypic and genotypic features in CMT type 2

Charcot-Marie-Tooth disease (CMT), or hereditary motor and sensory neuropathy (HMSN), includes two main subtypes of CMT1/HMSN I (demyelinating), and CMT2/HMSN II (axonal). Further heterogeneity has been demonstrated by genetic molecular studies, with at least four responsible genes for CMT1. As for CMT2, a mutation in the neurofilament-light (NF-L) gene has been identified in a single family, and other CMT2 loci have been mapped. We propose a clinical classification of the CMT2 phenotypes, and review the features of the identified CMT2 genotypes. The following main subtypes of CMT2 are considered in the phenotype classification: classical CMT2, the variants of CMT2 showing atypical features that may represent either variance in the classical CMT2 phenotype or separate entities; CMT2 plus, i.e. complex forms with involvement of additional neural structures. The recognized CMT2 genotypes include: CMT2A (mapped to chromosome 1p35-36); CMT2B (3q13-22); CMT2C (with vocal cord paresis); CMT2D (7p14); CMT2E, related to a mutation in the NF-L gene on chromosome 8p21; proximal CMT2, or HMSN P (3q13.1); CMT2 with MPZ mutations; autosomal recessive CMT2 (1q21.2-q21.3); agenesis of the corpus callosum with sensorimotor neuronopathy (15q13-q15); CMT2 X-linked with deafness and mental retardation (Xq24-q26). The identified genotypes may correspond to previously described clinical subtypes of CMT2. In particular, classical CMT2 presents in association with NF-L gene mutation, in the only CMT2 family with known gene mutation, and in CMT2A patients. However, the features of classical CMT2 have been paradoxically reported also in families with MPZ mutation, and conversely several CMT2 families are not linked to the known CMT2 loci. Further cloning of the CMT2 genes will ultimately shed light on the pathogenic mechanism(s) implicated in the process of axonal degeneration, shared by the different CMT2 genotypes.

A clinicopathological observation of Nyssen-van Bogaert syndrome with second motor neuron degeneration: two distinct clinical entities

OBJECTIVES

To report a novel clinicopathological observation of Nyssen-van Bogaert syndrome. To compare this observation with those previously reported. To discuss the nosological entity of this syndrome. To define the exact etiopathogenic mechanism of the neurogenic amyotrophy occurring at the late stage of the disease.

MATERIALS AND METHODS

The patient was a 16-year-old girl who developed loss of vision and deafness at the age of 8. Ataxia with slight cerebellar signs were present by the age of 14. Over the next 2 years, she developed distal weakness and wasting of the legs with depressed ankle reflexes. She died at the age of 16. Deparaffinized sections of the brain, the brain stem, the cerebellum and the spinal cord were stained with haematoxylin & eosin (H&E), Nissl, Woelcke, Bodian, periodic acid-schiff (PAS), Sudan Black and Kluver Barera. Antibodies anti-GFAP, anti-MPB and anti-neurofilaments were used for immunohistochemical stainings following the avidin-biotin-peroxydase complex (ABC) methods.

RESULTS

The clinical pictures in our patient are similar to those previously reported in juvenile patients with optico-cochleo-dentate syndrome. Pathological study of the nervous system confirmed the diagnosis of Nyssen-van Bogaert syndrome and also showed a severe anterior horn, posterior horn and Clarke's column nerve cell degeneration with anterior root atrophy.

CONCLUSION

From these clinical and pathological data, the authors suggest to include Nyssen-van Bogaert syndrome among the group of multiple system atrophy, propose to divide this syndrome into 2 forms (an early infantile form and a juvenile form) and consider that the neurogenic amyotrophy occurring at the late stage of the disease in juvenile and adult patients is mainly caused by the second motor neuron involvement.

A gene for X-linked optic atrophy is closely linked to the Xp11.4-Xp11.2 region of the X chromosome

The aim of this study was to identify the chromosomal location of the disease-causing gene in a family apparently segregating X-linked optic atrophy. A large family of 45 individuals with a four-generation history of X-linked optic atrophy was reexamined in a full ophthalmic as well as electrophysiological examination. A DNA linkage analysis of the family was undertaken in order to identify the chromosomal location of the disease-causing gene. Linkage analysis was performed with 26 markers that spanned the entire X chromosome. The affected males showed very early onset and slow progression of the disease. Ophthalmic study of the female carriers did not reveal any abnormalities. Close linkage without recombination was found at the MAOB locus (maximum LOD score [Zmax] 4.19). The Zmax - 1 support interval was found at a recombination fraction of .076 distal and .018 proximal to MAOB. Multipoint linkage analysis placed the optic atrophy-causing gene in the Xp11.4-p11.21 interval between markers DXS993 and DXS991, whereas any other localization along the X chromosome could be excluded.

Autosomal recessive inheritance of hereditary motor and sensory neuropathy with optic atrophy

Three siblings are reported with childhood onset hereditary motor and sensory neuropathy (HMSN) and adult onset optic atrophy. Electrophysiological studies showed an axonal neuropathy and dysfunction of the retinal ganglion cells or optic nerve. The presumed mode of inheritance is autosomal recessive. This is the second family in which autosomal recessive inheritance of HMSN and optic atrophy (HMSN type VI) has been described, and the first in which electrophysiological studies have been reported.

A novel X-linked gene, DDP, shows mutations in families with deafness (DFN-1), dystonia, mental deficiency and blindness

In 1960, progressive sensorineural deafness (McKusick 304,700, DFN-1) was shown to be X-linked based on a description of a large Norwegian pedigree. More recently, it was shown that this original DFN-1 family represented a new type of recessive neurodegenerative syndrome characterized by postlingual progressive sensorineural deafness as the first presenting symptom in early childhood, followed by progressive dystonia, spasticity, dysphagia, mental deterioration, paranoia and cortical blindness. This new disorder, termed Mohr-Tranebjaerg syndrome (referred to here as DFN-1/MTS) was mapped to the Xq21.3-Xq22 region2. Using positional information from a patient with a 21-kb deletion in chromosome Xq22 and sensorineural deafness along with dystonia, we characterized a novel transcript lying within the deletion as a candidate for this complex syndrome. We now report small deletions in this candidate gene in the original DFN-1/MTS family, and in a family with deafness, dystonia and mental deficiency but not blindness. This gene, named DDP (deafness/ dystonia peptide), shows high levels of expression in fetal and adult brain. The DDP protein demonstrates striking similarity to a predicted Schizosaccharomyces pombe protein of no known function. Thus, is it likely that the DDP gene encodes an evolutionarily conserved novel polypeptide necessary for normal human neurological development.

The pathology of charcot-marie-tooth disease and related disorders

Approximately a quarter of a century ago, the disorders originally designated as Charcot-Marie-Tooth disease and Dejerine-Sottas disease were shown by combined clinical, electrophysiological and nerve biopsy studies to be genetically complex. In pathological terms they could be broadly classified into demyelinating neuropathies and axonopathies. Advances in the molecular genetics of these disorders, particularly for those with a demyelinating basis, have recently produced substantial new insights. The identification of mutations in genes for myelin proteins has provided the opportunity for investigating the precise mechanisms of these neuropathies, including the use of spontaneous and genetically engineered animal models.

Autosomal dominant optic atrophy with asymptomatic peripheral neuropathy

The association between hereditary motor and sensory neuropathy (HMSN) and optic atrophy has been termed HMSN type VI. The autosomal dominant inheritance of this syndrome is reported. Three generations were affected with optic atrophy, which differed in some respects from classic dominant optic atrophy, and an asymptomatic, mainly sensory, neuropathy.

Genetic heterogeneity of hereditary motor and sensory neuropathy type VI

Charcot-Marie-Tooth disease comprises a heterogeneous group of neurologic disorders that shape peripheral motor and sensory neuropathy. A classification of these disorders was proposed in 1975, defining seven types of hereditary motor and sensory neuropathy. Clinical features of hereditary motor and sensory neuropathy type VI are muscle weakness and atrophy in leg and hand muscles, leading to progressive disability and loss of vision and progressing to blindness due to optic atrophy. Hereditary motor and sensory neuropathy type VI was first reported in 1879 by Vizioli, who described a kinship in which a father and two sons presented with peroneal muscular atrophy in association with optic atrophy. Since then, at least nine similar cases have been reported: three sporadic cases, two pairs of siblings who were offspring of consanguineous parents, and one pair of siblings who were offspring of unrelated parents suggesting autosomal recessive inheritance. Vertical transmission has been reported only by Vizioli. We present a father and two offspring (one boy and one girl) with the above-mentioned characteristic features of hereditary motor and sensory neuropathy type VI. Vizioli's kinship and either an autosomal recessive or autosomal dominant pattern of inheritance.

[Charcot-Marie-Tooth disease. Clinical study in 45 patients]

Charcot-Marie-Tooth (CMT) disease is the commonest inherited peripheral neuropathy. The clinical study of 45 patients with CMT is presented. They were derived from Antonio Pedro Hospital of Universidade Federal Fluminense in Niteroi, RJ, Brazil. Such patients could be divided by the motor conduction velocity in two types: a demyelinating form or type I (11 cases) and an axonal form or type II (34 cases). The disease was inherited as an autosomal dominant trait in 23 patients and as an autosomal recessive trait in 7 cases. In 15 patients the disorder was sporadic. The age of onset was in most of our cases before the 20 years. All of them had distal weakness in lower limbs. 38.2% had also distal weakness in upper limbs. 80% had distal wasting of the lower limbs and 50% had distal wasting of upper limbs. The tendon reflexes were absent in 64% in lower limbs and in 28% in upper limbs. The sensitive impairment in the distal regions of the extremities was mild in most patients. We found enlargement of peripheral nerves in 7 patients of type I. Pes cavus was present in 21 cases and scoliosis in 7. We found postural tremor of hands in 6 patients. In 9 cases there were rare features as mental retardation, trigeminal nevralgia, optic atrophy, deafness and calf enlargement. In most of our cases the clinical course was very slow progressive. A greater severity was seen in our sporadic cases.

A new X linked recessive deafness syndrome with blindness, dystonia, fractures, and mental deficiency is linked to Xq22

X linked recessive deafness accounts for only 1.7% of all childhood deafness. Only a few of the at least 28 different X linked syndromes associated with hearing impairment have been characterised at the molecular level. In 1960, a large Norwegian family was reported with early onset progressive sensorineural deafness, which was indexed in McKusick as DFN-1, McKusick 304700. No associated symptoms were described at that time. This family has been restudied clinically. Extensive neurological, neurophysiological, neuroradiological, and biochemical, as well as molecular techniques, have been applied to characterise the X linked recessive syndrome. The family history and extensive characterisation of 16 affected males in five generations confirmed the X linked recessive inheritance and the postlingual progressive nature of the sensorineural deafness. Some obligate carrier females showed signs of minor neuropathy and mild hearing impairment. Restudy of the original DFN-1 family showed that the deafness is part of a progressive X linked recessive syndrome, which includes visual disability leading to cortical blindness, dystonia, fractures, and mental deficiency. Linkage analysis indicated that the gene was linked to locus DXS101 in Xq22 with a lod score of 5.37 (zero recombination). Based on lod-1 support interval of the multipoint analysis, the gene is located in a region spanning from 5 cM proximal to 3 cM distal to this locus. As the proteolipid protein gene (PLP) is within this region and mutations have been shown to be associated with non-classical PMD (Pelizaeus-Merzbacher disease), such as complex X linked hereditary spastic paraplegia, PLP may represent a candidate gene for this disorder. This family represents a new syndrome (Mohr-Tranebjaerg syndrome, MTS) and provides significant new information about a new X linked recessive sydromic type of deafness which was previously thought to be isolated deafness.

Sensory neuropathy in infantile onset spinocerebellar ataxia (IOSCA)

Infantile onset spinocerebellar ataxia with sensory neuropathy is a new, inherited multisystem disorder discovered in 19 Finnish patients. In order to define the neuropathy of the disease, we measured sensory nerve action potentials and nerve conduction velocities in 18 patients, and recorded somatosensory evoked potentials (SEP) in 10 patients and performed a sural nerve biopsy in 13 patients. The fixed and teased nerve fascicles were examined by light and electron microscopy, and the whole transverse section of a nerve fascicle was photographed and enlarged for morphometric measurements. Our investigation revealed an early onset, rapidly progressive axonal neuropathy: the sensory action potentials were decreased after the age of 2 and a severe loss of mainly large myelinated fibers was found.

Hereditary motor-sensory neuropathy (Charcot-Marie-Tooth disease) with nerve deafness: a new variant

Hereditary motor-sensory neuropathy with sensorineural deafness is described in a family; the neurologic features and deafness were apparent in early childhood and infancy. The clinical syndrome in the family was not closely linked to the Duffy blood group, nor was duplication demonstrated at the disease-associated locus 17 p11.2. This family may represent a different form of this heterogeneous disease.

Strachan's syndrome: variation on a theme

We report two patients of Afro-Caribbean origin with an ataxic neuropathy combined with visual loss and deafness. In previous reports of a similar syndrome most patients have been malnourished and have had mucocutaneous lesions, features which were absent in our patients.

Hereditary motor and sensory neuropathy with deafness, mental retardation and absence of large myelinated fibers

Two brothers with a presumably hereditary motor and sensory polyneuropathy (HMSN), sensory-neural hearing loss and mental retardation had clinical features and neuropathological changes in the sural nerve which may set the disorder apart from previously described types of HMSN. Consecutive sural nerve biopsies from one case showed absence of large myelinated fibers and a normal complement of small fibers. We infer from our findings that a developmental abnormality with faulty growth and subsequent axonal atrophy may be responsible.

Hereditary motor and sensory neuropathy (HMSN) and optic atrophy (HMSN type VI, Vizioli)

Clinical and electrophysiological findings are described in three patients with hereditary motor and sensory neuropathy in association with optic atrophy (HMSN VI). The optic atrophy was of the Leber type in a 15-year-old boy. In a 70-year-old patient, as in three members of his family, optic atrophy was associated with tapetoretinal degeneration. In addition to HMSN and optic atrophy a 20-year-old man suffered from sensorineural deafness. Electrophysiological studies indicated a neuronal form of neuropathy, as in HMSN II. Brainstem auditory evoked potentials also revealed subclinical involvement of the central auditory pathways in the patients without hearing defects.

Hereditary motor and sensory neuropathy type 1 (HMSN1) associated with cranial neuropathy: an autopsy case report

A family with hereditary motor and sensory neuropathy type 1 (HMSN1) is reported. Three patients suffered only pupillary abnormality, two patients showed Adie's syndrome and peripheral neuropathy, and one had cranial neuropathy. Adie's syndrome and severe peripheral neuropathy. Autopsy of the latter revealed reduction of myelinated nerve fibers in the trigeminal, facial and hypoglossal nerves. There was extensive degeneration of the posterior column of the spinal cord. At the anterior horns, loss of motor neurons was observed, particularly at the lumbar level. The anterior and posterior roots showed loss of myelinated fibers. HMSN1 is only rarely associated with cranial neuropathy, and this is probably the first autopsy-proved case.

Optic atrophy, hearing loss, and peripheral neuropathy

Here we report on two families with a previously apparently undescribed, autosomal dominant disorder resulting in optic atrophy and subsequent development of hearing loss and peripheral neuropathy. This disorder differs from previous syndromes resulting in this triad of effects both in the severity and early onset of the optic atrophy and in its mode of transmission. Review of published cases of optic atrophy + hearing loss + peripheral neuropathy suggests that there are at least three such specific disorders; classification of these published cases by first-appearing symptom also results in a clean division by most-likely inheritance.

Autosomal recessive hereditary motor and sensory neuropathy with mental retardation, optic atrophy and pyramidal signs

A syndrome is described, consisting of severe neurogenic distal wasting, generalised muscle weakness, absent ankle reflexes, pyramidal signs, mental retardation, optic atrophy and retinal colloid bodies. A sural nerve biopsy from one case showed loss of nerve fibres suggesting the diagnosis of hereditary motor and sensory neuropathy. Progression of the disorder was very slow, all patients still being able to walk more than 20 years after the onset. The persons affected with this syndrome were two brothers and their female cousin from a large Gujerati pedigree where consanguinity was high. Autosomal recessive inheritance is therefore suggested.

Auditory function in hereditary motor and sensory neuropathy (Charcot-Marie-Tooth disease)

Fourteen patients with hereditary motor and sensory neuropathy (HMSN), 12 of Type I and 2 of Type II, were assessed for auditory dysfunction. Five patients complained of hearing loss and all had pure-tone audiograms outside the normal range, while one patient who did not complain of hearing impairment also had an abnormal pure-tone audiogram. Assessment of loudness function, speech audiometry and brainstem auditory evoked potentials (BAEP) suggested that the hearing loss was the result of VIII nerve dysfunction, a conclusion supported by the abnormality of the electrocochleogram (ECochG) in one patient.

Dominant optic atrophy, deafness, ptosis, ophthalmoplegia, dystaxia, and myopathy. A new syndrome

Twenty-three members of a 96-member family exhibited an autosomal dominant disorder which has not previously been described. This disorder involves progressive optic atrophy, abnormal electroretinography without retinal pigment changes, and progressive sensorineural hearing loss usually evident in the first or second decade of life. In midlife, ptosis, ophthalmoplegia, dystaxia, and a nonspecific myopathy occur.

Autosomal recessive inheritance of Charcot-Marie-Tooth disease associated with sensorineural deafness

Three siblings with a combination of sensorineural deafness and the Charcot-Marie-Tooth syndrome have been investigated in a consanguineous Indian kindred. This syndrome, which to the best of our knowledge has not previously been reported, is probably inherited as an autosomal recessive trait.

Abnormal auditory evoked potentials in Déjérine-Sottas disease. Report of two cases with central acoustic and vestibular impairment

Two cases of hereditary motor sensory neuropathy type III (Déjérine-Sottas disease) examined by audiological, vestibular and electrophysiological methods are reported. In both cases there were signs of vestibular and acoustic central pathway involvement, shown by vestibular examination and by the study of auditory evoked potentials. The presence of central involvement in this hereditary neuropathy suggests central as well as peripheral myelin alteration.

Visual evoked potential abnormalities in Charcot-Marie-Tooth disease and comparison with Friedreich's ataxia

Pattern-reversal visual evoked potentials (VEPs), recorded in 15 visually asymptomatic patients fulfilling the clinical and electrophysiological criteria of Charcot-Marie-Tooth disease (CMTD), were abnormal in 5 and possibly abnormal in another 3. Five patients showed a prolongation of P100 latency, one a reduction of amplitude and one a possibly abnormal "scotomatous" waveform. In 9 cases abnormalities were detected on neuro-ophthalmological examination. These were poorly correlated with VEP abnormalities, except for patients with 2 or more clinical eye signs. Relative central scotomata were found in the patient with an abnormal waveform. VEP abnormalities, where present, were usually fairly comparable in the 2 eyes. In comparison with a group of Friedrich's ataxia cases there was a lower overall incidence of VEP abnormalities in CMTD, but little to suggest a qualitative difference in the nature of the visual pathway pathology. All 4 patients with unequivocally abnormal VEPs had experienced atypical symptoms suggestive of CNS involvement. In none of these was it possible to sustain an alternative diagnosis. It is concluded that a minor degree of visual pathway involvement may be present in many CMTD cases, in spite of the fact that optic atrophy is only rarely reported, and that the VEP latency may reflect the degree to which other parts of the CNS are involved.

Trigeminal and facial nerve involvement in Charcot-Marie-Tooth disease. An electrodiagnostic study

The electrically and optically elicited orbicularis oculi reflex (OOR) and facial nerve latency were investigated in eight patients from three families. Each had autosomal dominant peroneal muscular atrophy. In a family with the dominantly inherited hypertrophic type markedly delayed latencies of the early reflex component of the OOR were found while the facial nerve had remained unaffected. These findings were interpreted as an indicator for supraorbital nerve involvement. In the other two investigated families of hypertrophic and neuronal type, a prolonged facial nerve latency was demonstrable. In these cases the latency of the optically evoked blink reflex was also delayed, while the latency of the early reflex component of the OOR was within normal limits or only slightly delayed. It is assumed that the different degree of cranial nerve involvement in these families is the expression of their genetically determined peculiarities.