Two mutations in the HSN2 gene explain the high prevalence of HSAN2 in French Canadians

Expression pattern analysis and characterization of the hereditary sensory and autonomic neuropathy 2 A (HSAN2A) gene with no lysine kinase (WNK1) in human dorsal root ganglion

Inherited painless neuropathies arise due to genetic insults that either block the normal signaling of or destroy the sensory afferent neurons in the dorsal root ganglion (DRG) responsible for transducing noxious stimuli. Complete loss of these neurons leads to profound insensitivity to all sensory modalities including pain. Hereditary sensory and autonomic neuropathy type 2 (HSNAII) is a rare genetic neuropathy characterized by a progressive distal early onset sensory loss. This syndrome is caused by autosomal recessive mutations in the with-no-lysine protein kinase 1 (WNK1) serine-threonine kinase gene. Of interest, disease-associated mutations are found in the large exon, termed "HSN2," which encodes a 498 amino acid domain C-terminal to the kinase domain. These mutations lead to truncation of the HSN2-containing proteins through the addition of an early stop codon (nonsense mutation) leading to loss of the C-terminal domains of this large protein. The present study evaluates the transcripts, gene structure, and protein structure of HSN2-containing WNK1 splice variants in DRG and spinal cord in order to establish the basal expression patterns of WNK1 and HSN2-containing WNK1 splice variants using multiplex fluorescent situ hybridization. We hypothesized that these transcripts would be enriched in pain-sensing DRG neurons, and, potentially, that enrichment in nociceptive neurons was responsible for the painless phenotypes observed. However, our in-depth analyses revealed that the HSN2-WNK1 splice variants were ubiquitously expressed but were not enriched in tachykinin 1-expressing C-fiber neurons, a class of neurons with a highly nociceptive character. We subsequently identified other subpopulations of DRG neurons with higher levels of HSN2-WNK1 expression, including mechanosensory large fibers. These data are inconsistent with the hypothesis that this transcript is enriched in nociceptive fibers, and instead suggest it may be related to general axon maintenance, or that nociceptive fibers are more sensitive to the genetic insult. These findings clarify the molecular and cellular expression pattern of this painless neuropathy gene in human tissue.

Axon morphogenesis and maintenance require an evolutionary conserved safeguard function of Wnk kinases antagonizing Sarm and Axed

The molecular and cellular mechanisms underlying complex axon morphogenesis are still poorly understood. We report a novel, evolutionary conserved function for the Drosophila Wnk kinase (dWnk) and its mammalian orthologs, WNK1 and 2, in axon branching. We uncover that dWnk, together with the neuroprotective factor Nmnat, antagonizes the axon-destabilizing factors D-Sarm and Axundead (Axed) during axon branch growth, revealing a developmental function for these proteins. Overexpression of D-Sarm or Axed results in axon branching defects, which can be blocked by overexpression of dWnk or Nmnat. Surprisingly, Wnk kinases are also required for axon maintenance of adult Drosophila and mouse cortical pyramidal neurons. Requirement of Wnk for axon maintenance is independent of its developmental function. Inactivation of dWnk or mouse Wnk1/2 in mature neurons leads to axon degeneration in the adult brain. Therefore, Wnk kinases are novel signaling components that provide a safeguard function in both developing and adult axons.

The Complex Clinical and Genetic Landscape of Hereditary Peripheral Neuropathy

Hereditary peripheral neuropathy (HPN) is a complex group of neurological disorders caused by mutations in genes expressed by neurons and Schwann cells. The inheritance of a single mutation or multiple mutations in several genes leads to disease phenotype. Patients exhibit symptoms during development, at an early age or later in adulthood. Most of the mechanistic understanding about these neuropathies comes from animal models and histopathological analyses of postmortem human tissues. Diagnosis is often very complex due to the heterogeneity and overlap in symptoms and the frequent overlap between various genes and different mutations they possess. Some symptoms in HPN are common through different subtypes such as axonal degeneration, demyelination, and loss of motor and sensory neurons, leading to similar physiologic abnormalities. Recent advances in gene-targeted therapies, genetic engineering, and next-generation sequencing have augmented our understanding of the underlying pathogenetic mechanisms of HPN.

A novel biallelic single base insertion in WNK1 in a Pakistani family with congenital insensitivity to pain

Hereditary sensory and autonomic neuropathy type II (HSANII) is a rare, recessively inherited neurological condition frequently involving insensitivity to pain. The subtype, HSAN2A, results from mutations in the gene WNK1. We identified a consanguineous Pakistani family with three affecteds showing symptoms of HSANII. We performed microarray genotyping, followed by homozygosity-by-descent (HBD) mapping, which indicated several significant HBD regions, including ~6 Mb towards the terminus of chromosome 12p, spanning WNK1. Simultaneously, we performed whole exome sequencing (WES) on one of the affected brothers, and identified a homozygous 1 bp insertion variant, Chr12:978101dupA, within exon 10. This variant, confirmed to segregate in the family, is predicted to truncate the protein (NM_213655.4:c.3464delinsAC; p.(Thr1155Asnfs*11) and lead to nonsense-mediated mRNA decay of the transcript. Previous studies of congenital pain insensitivity/HSANII in Pakistani families have identified mutations in SCN9A. Our study identified a previously unreported WNK1 mutation segregating with congenital pain insensitivity/HSANII in a Pakistani family.

A novel nonsense mutation in WNK1/HSN2 associated with sensory neuropathy and limb destruction in four siblings of a large Iranian pedigree

Background

Hereditary sensory and autonomic neuropathy type 2 (HSAN2) is an autosomal recessive disorder with predominant sensory dysfunction and severe complications such as limb destruction. There are different subtypes of HSAN2, including HSAN2A, which is caused by mutations in WNK1/HSN2 gene.

Methods

An Iranian family with four siblings and autosomal recessive inheritance pattern whom initially diagnosed with HSAN2 underwent whole exome sequencing (WES) followed by segregation analysis.

Results

According to the filtering criteria of the WES data, a novel candidate variation, c.3718C > A in WNK1/HSN2 gene that causes p.Tyr1025* was identified. This variation results in a truncated protein with 1025 amino acids instead of the wild-type product with 2645 amino acids. Sanger sequencing revealed that the mutation segregates with disease status in the pedigree.

Conclusions

The identified novel nonsense mutation in WNK1/HSN2 in an Iranian HSAN2 pedigree presents allelic heterogeneity of this gene in different populations. The result of current study expands the spectrum of mutations of the HSN2 gene as the genetic background of HSAN2A as well as further supports the hypothesis that HSN2 is a causative gene for HSAN2A. However, it seems that more research is required to determine the exact effects of this product in the nervous system.

Arthropathy-related pain in a patient with congenital impairment of pain sensation due to hereditary sensory and autonomic neuropathy type II with a rare mutation in the WNK1/HSN2 gene: a case report

Background

Hereditary sensory and autonomic neuropathy (HSAN) type II with WNK1/HSN2 gene mutation is a rare disease characterized by early-onset demyelination sensory loss and skin ulceration. To the best of our knowledge, no cases of an autonomic disorder have been reported clearly in a patient with WNK/HSN2 gene mutation and only one case of a Japanese patient with the WNK/HSN2 gene mutation of HSAN type II was previously reported.

Case presentation

Here we describe a 54-year-old woman who had an early childhood onset of insensitivity to pain; superficial, vibration, and proprioception sensation disturbances; and several symptoms of autonomic failure (e.g., orthostatic hypotension, fluctuation in body temperature, and lack of urge to defecate). Genetic analyses revealed compound homozygous mutations in the WNK1/HSN2 gene (c.3237_3238insT; p.Asp1080fsX1). The patient demonstrated sensory loss in the “stocking and glove distribution” but could perceive visceral pain, such as menstrual or gastroenteritis pain. She experienced frequent fainting episodes. She had undergone exenteration of the left metatarsal because of metatarsal osteomyelitis at 18 years. Sural nerve biopsy revealed a severe loss of myelinated and unmyelinated nerves. She complained of severe pain in multiple joints, even on having pain impairment. Although non-steroidal anti-inflammatory drugs are generally more effective than acetaminophen for arthritis, in our case, they were ineffective and acetaminophen (2400 mg/day) adequately controlled her pain and improved quality of life. Over 3 months, the numerical rating scale, pain interference scale of the Brief Pain Inventory, and the Pain Catastrophizing Scale decreased from 6/10 to 3/10, from 52/70 to 20/70, and from 22/52 to 3/52 points, respectively.

Conclusions

This is the second reported case of a Japanese patient with WNK/HSN2 gene mutation of HSAN type II and the first reported case of an autonomic disorder in a patient with the WNK/HSN2 gene mutation. Acetaminophen adequately controlled arthropathy related pain in a patient with congenital impairment of pain sensation.

(WNK)ing at death: With-no-lysine (Wnk) kinases in neuropathies and neuronal survival

Members of With-no-lysine (WNK) family of serine-threonine kinase are key regulators of chloride ion transport in diverse cell types, controlling the activity and the surface expression of cation-chloride (Na(+)/K(+)-Cl(-)) co-transporters. Mutations in WNK1 and WNK4 are linked to a hereditary form of hypertension, and WNKs have been extensively investigated pertaining to their roles in renal epithelial ion homeostasis. However, some members of the WNK family and their splice isoforms are also expressed in the mammalian brain, and have been implicated in aspects of hereditary neuropathy as well as neuronal and glial survival. WNK2, which is exclusively enriched in neurons, is well known as an anti-proliferative tumor suppressor. WNK3, on the other hand, appears to promote cell survival as its inhibition enhances neuronal apoptosis. However, loss of WNK3 has been recently shown to reduce ischemia-associated brain damage. In this review, I surveyed the potentially context-dependent roles of WNKs in neurological disorders and neuronal survival.

Inherited neuropathies: clinical overview and update

Inherited neuropathy is a group of common neurologic disorders with heterogeneous clinical presentations and genetic causes. Detailed neuromuscular evaluations, including nerve conduction studies, laboratory testing, and histopathologic examination, can assist in identification of the inherited component beyond family history. Genetic testing increasingly enables definitive diagnosis of specific inherited neuropathies. Diagnosis, however, is often complex, and neurologic disability may have both genetic and acquired components in individual patients. The decision of which genetic test to order or whether to order genetic tests is often complicated, and the strategies to maximize the value of testing are evolving. Apart from rare inherited metabolic neuropathies, treatment approaches remain largely supportive. We provide a clinical update of the various types of inherited neuropathies, their differential diagnoses, and distinguishing clinical features (where available). A framework is provided for clinical evaluations, including the inheritance assessment, electrophysiologic examinations, and specific genetic tests.

Hereditary sensory and autonomic neuropathies

Hereditary sensory and autonomic neuropathies (HSN/HSAN) are clinically and genetically heterogeneous disorders of the peripheral nervous system that predominantly affect the sensory and autonomic neurons. Hallmark features comprise not only prominent sensory signs and symptoms and ulcerative mutilations but also variable autonomic and motor disturbances. Autosomal dominant and autosomal recessive inheritance has been reported. Molecular genetics studies have identified disease-causing mutations in 11 genes. Some of the affected proteins have nerve-specific roles but underlying mechanisms have also been shown to involve sphingolipid metabolism, vesicular transport, structural integrity, and transcription regulation. Genetic and functional studies have substantially improved the understanding of the pathogenesis of the HSN/HSAN and will help to find preventive and causative therapies in the future.

Mutations in C5ORF42 cause Joubert syndrome in the French Canadian population

Joubert syndrome (JBTS) is an autosomal-recessive disorder characterized by a distinctive mid-hindbrain malformation, developmental delay with hypotonia, ocular-motor apraxia, and breathing abnormalities. Although JBTS was first described more than 40 years ago in French Canadian siblings, the causal mutations have not yet been identified in this family nor in most French Canadian individuals subsequently described. We ascertained a cluster of 16 JBTS-affected individuals from 11 families living in the Lower St. Lawrence region. SNP genotyping excluded the presence of a common homozygous mutation that would explain the clustering of these individuals. Exome sequencing performed on 15 subjects showed that nine affected individuals from seven families (including the original JBTS family) carried rare compound-heterozygous mutations in C5ORF42. Two missense variants (c.4006C>T [p.Arg1336Trp] and c.4690G>A [p.Ala1564Thr]) and a splicing mutation (c.7400+1G>A), which causes exon skipping, were found in multiple subjects that were not known to be related, whereas three other truncating mutations (c.6407del [p.Pro2136Hisfs*31], c.4804C>T [p.Arg1602*], and c.7477C>T [p.Arg2493*]) were identified in single individuals. None of the unaffected first-degree relatives were compound heterozygous for these mutations. Moreover, none of the six putative mutations were detected among 477 French Canadian controls. Our data suggest that mutations in C5ORF42 explain a large portion of French Canadian individuals with JBTS.

Mechanisms of disease in hereditary sensory and autonomic neuropathies

Hereditary sensory and autonomic neuropathies (HSANs) are a clinically and genetically heterogeneous group of disorders of the PNS. Progressive degeneration, predominantly of sensory and autonomic neurons, is the main pathological feature in patients with HSAN, and causes prominent sensory loss and ulcerative mutilations in combination with variable autonomic and motor disturbances. Advances in molecular genetics have enabled identification of disease-causing mutations in 12 genes, and studies on the functional effects of these mutations are underway. Although some of the affected proteins--such as nerve growth factor and its receptor--have obvious nerve-specific roles, others are ubiquitously expressed proteins that are involved in sphingolipid metabolism, vesicular transport, transcription regulation and structural integrity. An important challenge in the future will be to understand the common molecular pathways that result in HSANs. Unraveling the mechanisms that underlie sensory and autonomic neurodegeneration could assist in identifying targets for future therapeutic strategies in patients with HSAN. This Review highlights key advances in the understanding of HSANs, including insights into the molecular mechanisms of disease, derived from genetic studies of patients with these disorders.

KIF1A, an axonal transporter of synaptic vesicles, is mutated in hereditary sensory and autonomic neuropathy type 2

Hereditary sensory and autonomic neuropathy type II (HSANII) is a rare autosomal-recessive disorder characterized by peripheral nerve degeneration resulting in a severe distal sensory loss. Although mutations in FAM134B and the HSN2 exon of WNK1 were associated with HSANII, the etiology of a substantial number of cases remains unexplained. In addition, the functions of WNK1/HSN2 and FAM134B and their role in the peripheral nervous system remain poorly understood. Using a yeast two-hybrid screen, we found that KIF1A, an axonal transporter of synaptic vesicles, interacts with the domain encoded by the HSN2 exon. In parallel to this screen, we performed genome-wide homozygosity mapping in a consanguineous Afghan family affected by HSANII and identified a unique region of homozygosity located on chromosome 2q37.3 and spanning the KIF1A gene locus. Sequencing of KIF1A in this family revealed a truncating mutation segregating with the disease phenotype. Subsequent sequencing of KIF1A in a series of 112 unrelated patients with features belonging to the clinical spectrum of ulcero-mutilating sensory neuropathies revealed truncating mutations in three additional families, thus indicating that mutations in KIF1A are a rare cause of HSANII. Similarly to WNK1 mutations, pathogenic mutations in KIF1A were almost exclusively restricted to an alternatively spliced exon. This study provides additional insights into the molecular pathogenesis of HSANII and highlights the potential biological relevance of alternative splicing in the peripheral sensory nervous system.

Carriers of recessive WNK1/HSN2 mutations for hereditary sensory and autonomic neuropathy type 2 (HSAN2) are more sensitive to thermal stimuli

Hereditary sensory and autonomic neuropathy type 2 (HSAN2) is a rare recessive genetic disorder characterized by severe sensory loss affecting the tactile, thermal and nociceptive modalities. Although heterozygous carriers of nonsense mutations in the HSN2 gene, called with-no-lysine(K)-1 (WNK1), do not develop the disease, historical and experimental evidence suggests that these individuals might perceive somatosensory stimuli differently from others. Using the method-of-limits, we assessed the thresholds for warmth detection, cool detection, heat pain and cold pain in 25 mutation carriers and 35 controls. In group analyses, carriers displayed significantly lower warmth (p<0.001) and cool (p<0.05) difference thresholds, and also tended to report cold pain at higher temperatures (p=0.095), than controls. Similarly, matched-pair analyses showed that carriers are significantly more sensitive to warm stimuli (p<0.01) and cold pain stimuli (p<0.05), and tend to be more sensitive to cool stimuli (p=0.11). Furthermore, the differences between the warmth detection thresholds of the carriers and those of gender- and sex-matched wild types significantly increased with age (r=0.76, p=0.02), and in carriers cool detection thresholds did not increase with age (r=0.27, p=0.24) as expected and observed in controls (r=0.34, p=0.05). This study demonstrates that the carriers of a recessive mutation for HSAN2 display greater sensitivity to innocuous thermal stimuli, as well as for cold pain, suggesting a possible environmental adaptive advantage of the heterozygous state.

Current evidence for a modulation of low back pain by human genetic variants

The manifestation of chronic back pain depends on structural, psychosocial, occupational and genetic influences. Heritability estimates for back pain range from 30% to 45%. Genetic influences are caused by genes affecting intervertebral disc degeneration or the immune response and genes involved in pain perception, signalling and psychological processing. This inter-individual variability which is partly due to genetic differences would require an individualized pain management to prevent the transition from acute to chronic back pain or improve the outcome. The genetic profile may help to define patients at high risk for chronic pain. We summarize genetic factors that (i) impact on intervertebral disc stability, namely Collagen IX, COL9A3, COL11A1, COL11A2, COL1A1, aggrecan (AGAN), cartilage intermediate layer protein, vitamin D receptor, metalloproteinsase-3 (MMP3), MMP9, and thrombospondin-2, (ii) modify inflammation, namely interleukin-1 (IL-1) locus genes and IL-6 and (iii) and pain signalling namely guanine triphosphate (GTP) cyclohydrolase 1, catechol-O-methyltransferase, mu opioid receptor (OPMR1), melanocortin 1 receptor (MC1R), transient receptor potential channel A1 and fatty acid amide hydrolase and analgesic drug metabolism (cytochrome P450 [CYP]2D6, CYP2C9).

Mutations in the nervous system--specific HSN2 exon of WNK1 cause hereditary sensory neuropathy type II

Hereditary sensory and autonomic neuropathy type II (HSANII) is an early-onset autosomal recessive disorder characterized by loss of perception to pain, touch, and heat due to a loss of peripheral sensory nerves. Mutations in hereditary sensory neuropathy type II (HSN2), a single-exon ORF originally identified in affected families in Quebec and Newfoundland, Canada, were found to cause HSANII. We report here that HSN2 is a nervous system-specific exon of the with-no-lysine(K)-1 (WNK1) gene. WNK1 mutations have previously been reported to cause pseudohypoaldosteronism type II but have not been studied in the nervous system. Given the high degree of conservation of WNK1 between mice and humans, we characterized the structure and expression patterns of this isoform in mice. Immunodetections indicated that this Wnk1/Hsn2 isoform was expressed in sensory components of the peripheral nervous system and CNS associated with relaying sensory and nociceptive signals, including satellite cells, Schwann cells, and sensory neurons. We also demonstrate that the novel protein product of Wnk1/Hsn2 was more abundant in sensory neurons than motor neurons. The characteristics of WNK1/HSN2 point to a possible role for this gene in the peripheral sensory perception deficits characterizing HSANII.

Founder SH3TC2 mutations are responsible for a CMT4C French-Canadians cluster

Charcot-Marie-Tooth polyneuropathies (CMT) are clinically and genetically heterogeneous. We describe a French-Canadian cluster of 17 recessive CMT cases belonging to 10 families with variable early-onset CMT and scoliosis. The patients demonstrate great intra- and inter-familial variability. Linkage analysis confirmed that all families are linked to CMT4C locus on chromosome 5q32 (multipoint LOD score of 9.06). Haplotype analysis suggests that two SH3TC2 mutations are present in this cohort. The majority of carrier chromosomes, 26 of 34 (76%), carry the c.2860C-->T mutation. Despite extensive sequencing, the other mutation is not yet uncovered. This study demonstrates that the clinical variability observed in CMT4C is due to other factors than the nature of the mutation and that further work is needed to better define the SH3TC2 gene to ensure the identification of all CMT4C mutations.

[Hereditary ataxias, spastic parapareses and neuropathies in Eastern Canada]

It has been demonstrated, for many inherited diseases, that historical events have shaped the various regional gene pools of Eastern Canada. In so doing, it has given rise to the increased prevalence of some rare diseases due, to founder effects. The following neurogenetic disorders were first identified in patients from Eastern Canada: AOA-2, Arsacs, HSN-2, Arca-1, HMSN/ACC and Arsal. The population of Eastern Canada, we are convinced, will still allow the identification of new rare forms of hereditary ataxias, spastic parapareses and neuropathies as well as contribute to the uncovering of their mutated genes. We have summarized our current knowledge of the various hereditary ataxias, spastic parapareses and neuropathies in Eastern Canada. The study of the more common and homogenous features of these diseases has been largely completed.

Genetic mutations that prevent pain: implications for future pain medication

Part of the interindividual variability in pain therapy has been associated with genetic polymorphisms. Several genetic variants prevent or at least decrease pain in their carriers as compared with carriers of the respective wild-type or common alleles by impeding the generation, transmission and processing of nociceptive information or by increasing the local availability of active analgesics or their pharmacodynamic effects. Complete prevention of pain has so far been seen in six distinct rare hereditary syndromes, namely the ‘channelopathy-associated insensitivity to pain’, caused by 13 currently identified variants in the SCN9A gene coding for the α-subunit of the voltage-gated sodium channel, and five maladies belonging to the hereditary sensory and autonomic neuropathy (HSAN) I–V syndromes, caused by various mutations in several genes. Reduced pain in the average population has been associated with frequent variants in the µ-opioid receptor gene (OPRM1), catechol-O-methyltransferase gene (COMT), guanosine triphosphate cyclohydrolase 1/dopa-responsive dystonia gene (GCH1), transient receptor potential cation channel, subfamily V, member 1 gene (TRPV1) or the melanocortin-1 receptor gene (MC1R). Duplications/amplifications of the cytochrome P450 2D6 (CYP2D6) gene leading to increased enzyme function may cause intense opioid effects of codeine up to toxicity. The COMT V158M variant has been associated with decreased morphine requirements for analgesia. Inactivating MC1R variants have been associated with increased opioid analgesia of the µ-opioid receptor agonist morphine-6-glucuronide and, in women only, of κ-opioid agonists. Finally, variants in the P-glycoprotein gene (ABCB1) conferring decreased transporter function have been associated with increased respiratory depressive effects of fentanyl. In summary, a finite number of genetic variants that prevent pain by decreasing nociception or increasing analgesia have been identified. Given the complex biological and psychological nature of pain, we will see in the near future how much of the interindividual variance in pain and analgesia is due to identifiable genetic causes, and to what extent genetics enters clinical pain therapy.

Molecular genetics of hereditary sensory neuropathies

Hereditary sensory neuropathies (HSN), also known as hereditary sensory and autonomic neuropathies (HSAN), are a clinically and genetically heterogeneous group of disorders. They are caused by neuronal atrophy and degeneration, predominantly affecting peripheral sensory and autonomic neurons. Both congenital and juvenile to adulthood onset is possible. Currently, the classification of the HSN depends on the mode of inheritance, age at onset, and clinical presentation. Hallmark features are progressive sensory loss, chronic skin ulcers, and other skin abnormalities. Spontaneous fractures and neuropathic arthropathy are frequent complications and often necessitate amputations. Autonomic features vary between different subgroups. Distal muscle weakness and wasting may be present and is sometimes so prominent that it becomes difficult to distinguish HSN from Charcot-Marie-Tooth syndrome. Recent major advances in molecular genetics have led to the identification of seven gene loci and six-disease causing genes for autosomal-dominant and autosomal-recessive HSN. These genes have been shown to play roles in lipid metabolism and the regulation of intracellular vesicular transport, but also a presumptive transcriptional regulator, a nerve growth factor receptor, and a nerve growth factor have been described among the causative genes in HSN. Nevertheless, it remains unclear how mutations in the known genes lead to the phenotype of HSN. In this review, we summarize the recent progress of the molecular genetics of the HSN and the implicated genes.

Recent advances in hereditary sensory and autonomic neuropathies

PURPOSE OF REVIEW

This review summarizes the genetic advances of hereditary sensory neuropathies and hereditary sensory and autonomic neuropathies, and provides information on phenotype-genotype correlation and on possible underlying pathomechanisms.

RECENT FINDINGS

Hereditary sensory neuropathies, also known as hereditary sensory and autonomic neuropathies, are a clinically and genetically heterogeneous group of disorders. These disorders are characterized by prominent sensory loss with acro-mutilating complications and a variable degree of motor and autonomic disturbances. Based on age at onset, clinical features and mode of inheritance, these disorders have originally been subdivided into five types. The identification of eight loci and six disease-causing genes for this group of disorders, however, has shown that this present classification has to be refined.

SUMMARY

This review will discuss each of the different loci and genes of these disorders, showing glimpses into a possible underlying pathomechanism leading to the degeneration of sensory and autonomic neurons.

Novel mutation in the HSN2 gene in a Korean patient with hereditary sensory and autonomic neuropathy type 2

Hereditary sensory and autonomic neuropathies (HSAN) are a group of clinically and genetically heterogeneous disorders that are associated with sensory dysfunction. Among these, HSAN type 2 (HSAN2; MIM 201300) is a rare recessive disease that is characterized by an early age of onset with distal and proximal sensory loss, dysfunction of the autonomic nervous system, loss of the tendon reflex, the presence of various mutilations, and the slow progression of the disease over time. The authors report a Korean patient with the clinical features of HSAN2, who was compound heterozygous for two loss-of-function mutations in the HSN2 gene: c.217C > T (Gln73X) and c.1134_1135insT (Asp379fsX1). The Gln73X mutation was a novel mutation while the Asp379fsX1 mutation has recently been reported in a Japanese patient with HSAN2. These results expanded the spectrum of mutations of the HSN2 gene by identifying a novel truncating mutation in a Korean patient and further support the hypothesis that HSN2 is a causative gene for HSAN2.

Hereditary ataxia, spastic paraparesis and neuropathy in the French-Canadian population

Historical events have shaped the various regional gene pools of the French-Canadian (FC) population, leading to increased prevalence of some rare diseases. The first studies of these founder effects were performed in large part by astute clinicians such as André Barbeau. In collaboration with others, he contributed greatly to the delineation of phenotypic subtypes of these conditions. As such, the following neurogenetic disorders were first identified in patients of FC origin: AOA2, ARSACS, HSAN2, RAB, and HMSN/ACC. We have summarized our current knowledge of the main hereditary ataxias, spastic parapareses and neuropathies that are particular to the FC population. The initial genetic characterization of the more common and homogeneous of these diseases has been largely completed. We predict that the regional populations of Canada will allow the identification of new rare forms of hereditary ataxias, spastic parapareses and neuropathies, and contribute to the unravelling of the genetic basis of these entities.

Disease mechanisms in hereditary sensory and autonomic neuropathies

Inherited peripheral neuropathies are common monogenically inherited diseases of the peripheral nervous system. In the most common variant, i.e., the hereditary motor and sensory neuropathies, both motor and sensory nerves are affected. In contrast, sensory abnormalities predominate or are exclusively present in hereditary sensory and autonomic neuropathies (HSAN). HSAN are clinically and genetically heterogeneous and are subdivided according to mode of inheritance, age of onset and clinical evolution. In recent years, 6 disease-causing genes have been identified for autosomal dominant and recessive HSAN. However, vesicular transport and axonal trafficking seem important common pathways leading to degeneration of sensory and autonomic neurons. This review discusses the HSAN-related genes and their biological role in the disease mechanisms leading to HSAN.