Leukoencephalopathy and conduction blocks in PLEKHG5-associated intermediate CMT disease.

Biallelic variants in PLEKHG5 have been reported so far associated with different clinical phenotypes including Lower motor neuron disease (LMND) [also known as distal hereditary motor neuropathies (dHMN or HMN) or distal spinal muscular atrophy (DSMA4)] and intermediate Charcot-Marie-Tooth disease (CMT). We report four patients from two families presenting with intermediate CMT and atypical clinical and para-clinical findings. Patients presented with predominant distal weakness with none or mild sensory involvement and remain ambulant at last examination (22-36 years). Nerve conduction studies revealed, in all patients, intermediate motor nerve conduction velocities, reduced sensory amplitudes and multiple conduction blocks in upper limbs, outside of typical nerve compression sites. CK levels were strikingly elevated (1611-3867 U/L). CSF protein content was mildly elevated in two patients. Diffuse bilateral white matter lesions were detected in one patient. Genetic analysis revealed three novel frameshift variants c.1835_1860del and c.2308del (family 1) and c.104del (family 2). PLEKHG5-associated disease ranges from pure motor phenotypes with predominantly proximal involvement to intermediate CMT with predominant distal motor involvement and mild sensory symptoms. Leukoencephalopathy, elevated CK levels and the presence of conduction blocks associated with intermediate velocities in NCS are part of the phenotype and may arise suspicion of the disease, thus avoiding misdiagnosis and unnecessary therapeutics in these patients.

Towards a functional pathology of hereditary neuropathies.

A growing number of hereditary neuropathies have been assigned to causative gene defects in recent years. The study of human nerve biopsy samples has contributed substantially to the discovery of many of these neuropathy genes. Genotype-phenotype correlations based on peripheral nerve pathology have provided a comprehensive picture of the consequences of these mutations. Intriguingly, several gene defects lead to distinguishable lesion patterns that can be studied in nerve biopsies. These characteristic features include the loss of certain nerve fiber populations and a large spectrum of distinct structural changes of axons, Schwann cells and other components of peripheral nerves. In several instances the lesion patterns are directly or indirectly linked to the known functions of the mutated gene. The present review is designed to provide an overview on these characteristic patterns. It also considers other aspects important for the manifestation and pathology of hereditary neuropathies including the role of inflammation, effects of chemotherapeutic agents and alterations detectable in skin biopsies.

Loss-of-Function Mutations in FRRS1L Lead to an Epileptic-Dyskinetic Encephalopathy.

Glutamatergic neurotransmission governs excitatory signaling in the mammalian brain, and abnormalities of glutamate signaling have been shown to contribute to both epilepsy and hyperkinetic movement disorders. The etiology of many severe childhood movement disorders and epilepsies remains uncharacterized. We describe a neurological disorder with epilepsy and prominent choreoathetosis caused by biallelic pathogenic variants in FRRS1L, which encodes an AMPA receptor outer-core protein. Loss of FRRS1L function attenuates AMPA-mediated currents, implicating chronic abnormalities of glutamatergic neurotransmission in this monogenic neurological disease of childhood.

Underestimated associated features in CMT neuropathies: clinical indicators for the causative gene?

INTRODUCTION: Charcot-Marie-Tooth neuropathy (CMT) is a genetically heterogeneous group of peripheral neuropathies. In addition to the classical clinical phenotype, additional features can occur. METHODS: We studied a wide range of additional features in a cohort of 49 genetically confirmed CMT patients and performed a systematic literature revision. RESULTS: Patients harbored a PMP22 gene alteration (n = 28) or a mutation in MPZ (n = 11), GJB1 (n = 4), LITAF (n = 2), MFN2 (n = 2), INF2 (n = 1), NEFL (n = 1). We identified four novel mutations (3 MPZ, 1 GJB1). A total of 88% presented at least one additional feature. In MPZ patients, we detected hypertrophic nerve roots in 3/4 cases that underwent spinal MRI, and pupillary abnormalities in 27%. In our cohort, restless legs syndrome (RLS) was present in 18%. We describe for the first time RLS associated with LITAF or MFN2 and predominant upper limb involvement with LITAF. Cold-induced hand cramps occurred in 10% (PMP22,MPZ,MFN2), and autonomous nervous system involvement in 18% (PMP22,MPZ, LITAF,MFN2). RLS and respiratory insufficiency were mostly associated with severe neuropathy, and pupillary abnormalities with mild to moderate neuropathy. CONCLUSIONS: In CMT patients, additional features occur frequently. Some of them might be helpful in orienting genetic diagnosis. Our data broaden the clinical spectrum and genotype-phenotype associations with CMT.

Dysfunction in endoplasmic reticulum-mitochondria crosstalk underlies SIGMAR1 loss of function mediated motor neuron degeneration.

Mutations in Sigma 1 receptor (SIGMAR1) have been previously identified in patients with amyotrophic lateral sclerosis and disruption of Sigmar1 in mouse leads to locomotor deficits. However, cellular mechanisms underlying motor phenotypes in human and mouse with disturbed SIGMAR1 function have not been described so far. Here we used a combination of in vivo and in vitro approaches to investigate the role of SIGMAR1 in motor neuron biology. Characterization of Sigmar1(-/-) mice revealed that affected animals display locomotor deficits associated with muscle weakness, axonal degeneration and motor neuron loss. Using primary motor neuron cultures, we observed that pharmacological or genetic inactivation of SIGMAR1 led to motor neuron axonal degeneration followed by cell death. Disruption of SIGMAR1 function in motor neurons disturbed endoplasmic reticulum-mitochondria contacts, affected intracellular calcium signalling and was accompanied by activation of endoplasmic reticulum stress and defects in mitochondrial dynamics and transport. These defects were not observed in cultured sensory neurons, highlighting the exacerbated sensitivity of motor neurons to SIGMAR1 function. Interestingly, the inhibition of mitochondrial fission was sufficient to induce mitochondria axonal transport defects as well as axonal degeneration similar to the changes observed after SIGMAR1 inactivation or loss. Intracellular calcium scavenging and endoplasmic reticulum stress inhibition were able to restore mitochondrial function and consequently prevent motor neuron degeneration. These results uncover the cellular mechanisms underlying motor neuron degeneration mediated by loss of SIGMAR1 function and provide therapeutically relevant insight into motor neuronal diseases.

Ophthalmic features of PLA2G6-related paediatric neurodegeneration with brain iron accumulation.

BACKGROUND: Neurodegeneration with brain iron accumulation (NBIA) refers to genetically heterogenous paediatric neurodegenerative disorders characterised by basal ganglia iron deposition. One major cause is recessive mutations in the PLA2G6 gene. While strabismus and optic nerve pallor have been reported for PLA2G6-related disease, the ophthalmic phenotype is not carefully defined. In this study we characterise the ophthalmic phenotype of PLA2G6-related NBIA. METHODS: Prospective cohort study. RESULTS: The eight patients were 4-26 years old when examined. All had progressive cognitive and motor regression first noted between 9 months and 6 years of age that typically first manifested as difficulty walking (ataxia). Ophthalmic examination was sometimes limited by cognitive ability. Four of eight had exotropia, 7/7 bilateral supraduction defect, 5/7 poor convergence, 6/8 saccadic pursuit, 4/8 saccadic intrusions that resembled square-wave jerks, and 8/8 bilateral optic nerve head pallor. All patients lacked Bell phenomenon. CONCLUSIONS: Upgaze palsy, although not a previously reported finding, was confirmed in all patients (except in one for whom assessment could not be performed) and thus can be considered part of the phenotype in children and young adults. Other frequent findings not previously highlighted were abnormal convergence, saccadic pursuit, and saccadic intrusions. Optic nerve head pallor and strabismus, previously reported findings in the disease, were found in 100% and 50% of our cohort, respectively, and the strabismus in our series was always exotropia. Taken together, these clinical findings may be helpful in distinguishing PLA2G6-related neurodegeneration from the other major cause of NBIA, recessive PANK2 mutations.

C19orf12 mutation leads to a pallido-pyramidal syndrome.

Pallido-pyramidal syndromes combine dystonia with or without parkinsonism and spasticity as part of a mixed neurodegenerative disorder. Several causative genes have been shown to lead to pallido-pyramidal syndromes, including FBXO7, ATP13A2, PLA2G6, PRKN and SPG11. Among these, ATP13A2 and PLA2G6 are inconsistently associated with brain iron deposition. Using homozygosity mapping and direct sequencing in a multiplex consanguineous Saudi Arabian family with a pallido-pyramidal syndrome, iron deposition and cerebellar atrophy, we identified a homozygous p.G53R mutation in C19orf12. Our findings add to the phenotypic spectrum associated with C19orf12 mutations.

New findings in a global approach to dissect the whole phenotype of PLA2G6 gene mutations.

Mutations in PLA2G6 gene have variable phenotypic outcome including infantile neuroaxonal dystrophy, atypical neuroaxonal dystrophy, idiopathic neurodegeneration with brain iron accumulation and Karak syndrome. The cause of this phenotypic variation is so far unknown which impairs both genetic diagnosis and appropriate family counseling. We report detailed clinical, electrophysiological, neuroimaging, histologic, biochemical and genetic characterization of 11 patients, from 6 consanguineous families, who were followed for a period of up to 17 years. Cerebellar atrophy was constant and the earliest feature of the disease preceding brain iron accumulation, leading to the provisional diagnosis of a recessive progressive ataxia in these patients. Ultrastructural characterization of patients' muscle biopsies revealed focal accumulation of granular and membranous material possibly resulting from defective membrane homeostasis caused by disrupted PLA2G6 function. Enzyme studies in one of these muscle biopsies provided evidence for a relatively low mitochondrial content, which is compatible with the structural mitochondrial alterations seen by electron microscopy. Genetic characterization of 11 patients led to the identification of six underlying PLA2G6 gene mutations, five of which are novel. Importantly, by combining clinical and genetic data we have observed that while the phenotype of neurodegeneration associated with PLA2G6 mutations is variable in this cohort of patients belonging to the same ethnic background, it is partially influenced by the genotype, considering the age at onset and the functional disability criteria. Molecular testing for PLA2G6 mutations is, therefore, indicated in childhood-onset ataxia syndromes, if neuroimaging shows cerebellar atrophy with or without evidence of iron accumulation.

PLEKHG5 deficiency leads to an intermediate form of autosomal-recessive Charcot-Marie-Tooth disease.

Charcot-Marie-Tooth disease (CMT) comprises a clinically and genetically heterogeneous group of peripheral neuropathies characterized by progressive distal muscle weakness and atrophy, foot deformities and distal sensory loss. Following the analysis of two consanguineous families affected by a medium to late-onset recessive form of intermediate CMT, we identified overlapping regions of homozygosity on chromosome 1p36 with a combined maximum LOD score of 5.4. Molecular investigation of the genes from this region allowed identification of two homozygous mutations in PLEKHG5 that produce premature stop codons and are predicted to result in functional null alleles. Analysis of Plekhg5 in the mouse revealed that this gene is expressed in neurons and glial cells of the peripheral nervous system, and that knockout mice display reduced nerve conduction velocities that are comparable with those of affected individuals from both families. Interestingly, a homozygous PLEKHG5 missense mutation was previously reported in a recessive form of severe childhood onset lower motor neuron disease (LMND) leading to loss of the ability to walk and need for respiratory assistance. Together, these observations indicate that different mutations in PLEKHG5 lead to clinically diverse outcomes (intermediate CMT or LMND) affecting the function of neurons and glial cells.

KIF1A missense mutations in SPG30, an autosomal recessive spastic paraplegia: distinct phenotypes according to the nature of the mutations.

The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases characterised by progressive spasticity in the lower limbs. The nosology of autosomal recessive forms is complex as most mapped loci have been identified in only one or a few families and account for only a small percentage of patients. We used next-generation sequencing focused on the SPG30 chromosomal region on chromosome 2q37.3 in two patients from the original linked family. In addition, wide genome scan and candidate gene analysis were performed in a second family of Palestinian origin. We identified a single homozygous mutation, p.R350G, that was found to cosegregate with the disease in the SPG30 kindred and was absent in 970 control chromosomes while affecting a strongly conserved amino acid at the end of the motor domain of KIF1A. Homozygosity and linkage mapping followed by mutation screening of KIF1A allowed us to identify a second mutation, p.A255V, in the second family. Comparison of the clinical features with the nature of the mutations of all reported KIF1A families, including those reported recently with hereditary sensory and autonomic neuropathy, suggests phenotype-genotype correlations that may help to understand the mechanisms involved in motor neuron degeneration. We have shown that mutations in the KIF1A gene are responsible for SPG30 in two autosomal recessive HSP families. In published families, the nature of the KIF1A mutations seems to be of good predictor of the underlying phenotype and vice versa.

Screening of ARHSP-TCC patients expands the spectrum of SPG11 mutations and includes a large scale gene deletion.

Autosomal recessive spastic paraplegia with thinning of corpus callosum (ARHSP-TCC) is a complex form of HSP initially described in Japan but subsequently reported to have a worldwide distribution with a particular high frequency in multiple families from the Mediterranean basin. We recently showed that ARHSP-TCC is commonly associated with mutations in SPG11/KIAA1840 on chromosome 15q. We have now screened a collection of new patients mainly originating from Italy and Brazil, in order to further ascertain the spectrum of mutations in SPG11, enlarge the ethnic origin of SPG11 patients, determine the relative frequency at the level of single Countries (i.e., Italy), and establish whether there is one or more common mutation. In 25 index cases we identified 32 mutations; 22 are novel, including 9 nonsense, 3 small deletions, 4 insertions, 1 in/del, 1 small duplication, 1 missense, 2 splice-site, and for the first time a large genomic rearrangement. This brings the total number of SPG11 mutated patients in the SPATAX collection to 111 cases in 44 families and in 17 isolated cases, from 16 Countries, all assessed using homogeneous clinical criteria. While expanding the spectrum of mutations in SPG11, this larger series also corroborated the notion that even within apparently homogeneous population a molecular diagnosis cannot be achieved without full gene sequencing.

Mutations in SPG11 are frequent in autosomal recessive spastic paraplegia with thin corpus callosum, cognitive decline and lower motor neuron degeneration.

Hereditary spastic paraplegias (HSP) are neurodegenerative diseases mainly characterized by lower limb spasticity associated, in complicated forms, with additional neurological signs. We have analysed a large series of index patients (n = 76) with this condition, either from families with an autosomal recessive inheritance (n = 43) or isolated patients (n = 33), for mutations in the recently identified SPG11 gene. We found 22 truncating mutations, including the first four splice-site mutations, segregating in seven isolated cases and 13 families. Nineteen mutations were novel. Two recurrent mutations were found in Portuguese and North-African patients indicating founder effects in these populations. The mutation frequency varied according to the phenotype, from 41%, in HSP patients presenting with a thin corpus callosum (TCC) visualized by MRI, to 4.5%, in patients with mental impairment without a TCC. Disease onset occurred during the first to the third decade mainly by problems with gait and/or mental retardation. After a mean disease duration of 14.9 +/- 6.6 years, the phenotype of 38 SPG11 patients was severe with 53% of patients wheelchair bound or bedridden. In addition to mental retardation, 80% of the patients showed cognitive decline with executive dysfunction. Interestingly, the phenotype also frequently included lower motor neuron degeneration (81%) with wasting (53%). Slight ocular cerebellar signs were also noted in patients with long disease durations. In addition to a TCC (95%), brain MRI revealed white matter alterations (69%) and cortical atrophy (81%), which worsened with disease duration. In conclusion, our study reveals the high frequency of SPG11 mutations in patients with HSP, a TCC and cognitive impairment, including in isolated patients, and extends the associated phenotype.

Spastic paraplegia 5: Locus refinement, candidate gene analysis and clinical description.

Thirty-three different loci for hereditary spastic paraplegias (HSP) have been mapped, and 15 responsible genes have been identified. Autosomal recessive spastic paraplegias (ARHSPs) usually have clinically complex phenotypes but the SPG5, SPG24, and SPG28 loci are considered to be associated with pure forms of the disease. We performed a genome-wide scan in a large French family. Fine mapping of the refined SPG5 region on chromosome 8q12 was performed in another 17 ARHSP families with additional microsatellite markers. After exclusion of known ARHSP loci, the genome-wide screen provided evidence of linkage with a maximal multipoint lod score of 2.6 in the D8S1113-D8S1699 interval. This interval partially overlapped SPG5 and reduced it to a 5.9 megabase (Mb)-region between D8S1113 and D8S544. In a family of Algerian origin from a series of 17 other ARHSP kindreds, linkage to the SPG5 locus was supported by a multipoint lod score of 2.3. The direct sequencing of the coding exons of seven candidate genes did not detect mutations/polymorphisms in the index cases of both linked families. The phenotype of the two SPG5-linked families consisted of spastic paraparesis associated with deep sensory loss. In several patients with long disease durations, there were also mild cerebellar signs. The frequency of SPG5 was approximately 10% (2/18) in our series of ARHSP families with pure or complex forms. We have refined the SPG5 locus to a 3.8 cM interval and extended the phenotype of this form of ARHSP to include slight cerebellar signs.

Autosomal recessive axonal Charcot-Marie-Tooth disease (ARCMT2): phenotype-genotype correlations in 13 Moroccan families.

Charcot-Marie-Tooth disease is a genetically heterogeneous group of hereditary motor and sensory neuropathies. Three loci for the axonal autosomal recessive subgroup (ARCMT2) have been reported in 1q21 (CMT2B1, LMNA), 8q21 (CMT4A and CMT2K, GDAP1) and 19q13 (CMT2B2). We report here a clinical, electrophysiological, pathological and genetic study in 13 Moroccan families with ARCMT2 phenotypes. Clinical and electrophysiological examinations were performed in all index cases and 64 'at-risk' relatives. Thirty-one patients were clinically affected. A peroneal nerve biopsy was obtained from three patients. Four families were linked to the 1q21 locus, all had the LMNA R298C mutation. Six families were linked to the 8q21 locus, all had the GDAP1 S194X mutation. Founder effects for both mutations were suggested by the analysis of microsatellite markers close to the genes. The three remaining families were excluded from the three known loci. The electrophysiological findings were consistent with an axonal neuropathy. The clinical data show that in CMT2B1 the disease began most often in the second decade and progressed gradually from distal to proximal muscles. Three of our patients with the longest disease durations (>24 years) had also severe impairment in the scapular muscles. Reported here for the first time, this might be a hallmark of CMT2B1. Patients with CMT4A/2K had onset most often before the age of 2 years. Most had severe clubfoot from the beginning, one of the hallmarks of CMT4A/2K. None of our patients with CMT4A/2K had vocal cord paralysis. The clinical phenotype of the three families that are not linked to the three known loci presented some particularities that were not seen in those with known genetic defects. One family was characterized by late onset of the disease (>20 years) or a mild neuropathy that was diagnosed only when the family was examined. In a second family, dorsal scoliosis was the most prominent symptom. In the third family, symptoms began in the second decade with a moderate neuropathy associated with a pronounced scoliosis. These families illustrate the extent of clinical and genetic heterogeneity in ARCMT2.

Mutations in SPG11, encoding spatacsin, are a major cause of spastic paraplegia with thin corpus callosum.

Autosomal recessive hereditary spastic paraplegia (ARHSP) with thin corpus callosum (TCC) is a common and clinically distinct form of familial spastic paraplegia that is linked to the SPG11 locus on chromosome 15 in most affected families. We analyzed 12 ARHSP-TCC families, refined the SPG11 candidate interval and identified ten mutations in a previously unidentified gene expressed ubiquitously in the nervous system but most prominently in the cerebellum, cerebral cortex, hippocampus and pineal gland. The mutations were either nonsense or insertions and deletions leading to a frameshift, suggesting a loss-of-function mechanism. The identification of the function of the gene will provide insight into the mechanisms leading to the degeneration of the corticospinal tract and other brain structures in this frequent form of ARHSP.

A novel locus for autosomal recessive spastic ataxia on chromosome 17p.

Autosomal recessive spastic ataxias are a heterogeneous group of neurodegenerative diseases usually characterized by the early onset of cerebellar and pyramidal signs. With the collaboration of the clinical European and Mediterranean SPATAX network, we identified 15 families with 34 affected members presenting with ataxia and pyramidal signs or spasticity that were not linked to the ARSACS locus on chromosome 13. In an informative consanguineous Moroccan family, we mapped a novel locus, SAX2, to chromosome 17p13. The minimal linked interval lies in a region of 6.1 cM flanked by markers D17S1845/1583 and D17S1854 (Z(max) = 3.21). Three of the remaining 14 families were also possibly linked to SAX2. The overall clinical picture in nine patients was cerebellar ataxia with pyramidal signs and/or spasticity. Onset occurred before the age of 15 years in two families and in adulthood in the other two. Interestingly, in the largest SAX2 family, the presenting clinical sign was dysarthria, which is not common in other forms of inherited ataxias or spastic ataxias, whereas gait difficulties appeared later. Most cases also showed fasciculations suggesting that both lower and upper motor neurons are involved in the disease process. No mutations were found in the coding exons of KIF1C, ARRB2 and ANKFY1, three genes in the candidate region.

Spastic paraplegia with thin corpus callosum: description of 20 new families, refinement of the SPG11 locus, candidate gene analysis and evidence of genetic heterogeneity.

We studied 20 Mediterranean families (40 patients) with autosomal recessive hereditary spastic paraplegia and thin corpus callosum (ARHSP-TCC, MIM 604360) to characterize their clinical and genetic features. In six families (17 patients) of Algerian Italian, Moroccan, and Portuguese ancestry, we found data consistent with linkage to the SPG11 locus on chromosome 15q13-15, whereas, in four families (nine patients of Italian, French, and Portuguese ancestry) linkage to the SPG11 locus could firmly be excluded, reinforcing the notion that ARHSP-TCC is genetically heterogeneous. Patients from linked and unlinked families could not be distinguished on the basis of clinical features alone. In SPG11-linked kindred, haplotype reconstruction allowed significant refinement to 6 cM, of the minimal chromosomal interval, but analysis of two genes (MAP1A and SEMA6D) in this region did not identify causative mutations. Our findings suggest that ARHSP-TCC is the most frequent form of ARHSP in Mediterranean countries and that it is particularly frequent in Italy.

Autosomal recessive spastic paraplegia (SPG30) with mild ataxia and sensory neuropathy maps to chromosome 2q37.3.

The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases characterized by progressive spasticity in the lower limbs. Twenty-nine different loci (SPG) have been mapped so far, and 11 responsible genes have been identified. Clinically, one distinguishes between pure and complex HSP forms which are variably associated with numerous combinations of neurological and extra-neurological signs. Less is known about autosomal recessive forms (ARHSP) since the mapped loci have been identified often in single families and account for only a small percentage of patients. We report a new ARHSP locus (SPG30) on chromosome 2q37.3 in a consanguineous family with seven unaffected and four affected members of Algerian origin living in Eastern France with a significant multipoint lod score of 3.8. Ten other families from France (n = 4), Tunisia (n = 2), Algeria (n = 3) and the Czech Republic (n = 1) were not linked to the newly identified locus thus demonstrating further genetic heterogeneity. The phenotype of the linked family consists of spastic paraparesis and peripheral neuropathy associated with slight cerebellar signs confirmed by cerebellar atrophy on one CT scan.