The gene for hereditary sensory neuropathy type I (HSN-I) maps to chromosome 9q22.1-q22.3

Serine Palmitoyltransferase (SPT)-related Neurodegenerative and Neurodevelopmental Disorders

Motor neuron diseases and peripheral neuropathies are heterogeneous groups of neurodegenerative disorders that manifest with distinct symptoms due to progressive dysfunction or loss of specific neuronal subpopulations during different stages of development. A few monogenic, neurodegenerative diseases associated with primary metabolic disruptions of sphingolipid biosynthesis have been recently discovered. Sphingolipids are a subclass of lipids that form critical building blocks of all cellular and subcellular organelle membranes including the membrane components of the nervous system cells. They are especially abundant within the lipid portion of myelin. In this review, we will focus on our current understanding of disease phenotypes in three monogenic, neuromuscular diseases associated with pathogenic variants in components of serine palmitoyltransferase, the first step in sphingolipid biosynthesis. These include hereditary sensory and autonomic neuropathy type 1 (HSAN1), a sensory predominant peripheral neuropathy, and two neurodegenerative disorders: juvenile amyotrophic lateral sclerosis affecting the upper and lower motor neurons with sparing of sensory neurons, and a complicated form of hereditary spastic paraplegia with selective involvement of the upper motor neurons and more broad CNS neurodegeneration. We will also review our current understanding of disease pathomechanisms, therapeutic approaches, and the unanswered questions to explore in future studies.

PHF2 histone demethylase prevents DNA damage and genome instability by controlling cell cycle progression of neural progenitors

Histone H3 lysine 9 methylation (H3K9me) is essential for cellular homeostasis; however, its contribution to development is not well established. Here, we demonstrate that the H3K9me2 demethylase PHF2 is essential for neural progenitor proliferation in vitro and for early neurogenesis in the chicken spinal cord. Using genome-wide analyses and biochemical assays we show that PHF2 controls the expression of critical cell cycle progression genes, particularly those related to DNA replication, by keeping low levels of H3K9me3 at promoters. Accordingly, PHF2 depletion induces R-loop accumulation that leads to extensive DNA damage and cell cycle arrest. These data reveal a role of PHF2 as a guarantor of genome stability that allows proper expansion of neural progenitors during development.

Hereditary Sensory and Autonomic Neuropathies: Adding More to the Classification

PURPOSE OF REVIEW

Hereditary sensory and autonomic neuropathies (HSANs) are a clinically heterogeneous group of inherited neuropathies featuring prominent sensory and autonomic involvement. Classification of HSAN is based on mode of inheritance, genetic mutation, and phenotype. In this review, we discuss the recent additions to this classification and the important updates on management with a special focus on the recently investigated disease-modifying agents.

RECENT FINDINGS

In this past decade, three more HSAN types were added to the classification creating even more diversity in the genotype-phenotype. Clinical trials are underway for disease-modifying and symptomatic therapeutics, targeting mainly HSAN type III. Obtaining genetic testing leads to accurate diagnosis and guides focused management in the setting of such a diverse and continuously growing phenotype. It also increases the wealth of knowledge on HSAN pathophysiologies which paves the way toward development of targeted genetic treatments in the era of precision medicine.

The expression and biological function of the PHF2 gene in breast cancer

PHD Finger Protein 2 (PHF2), as a protein code and a transcription regulatory gene, is a member of the Jumonji-C domain (JmjC). PHF2 is located at human chromosome 9q22.31 and is frequently decreased in various malignancies. However, the definite role of PHF2 in breast cancer remains unclear. To detect the expression and function of PHF2 in breast cancer, a q-PCR assay was used to detect the mRNA expression of PHF2 in breast cancer cell lines and paired breast cancer tissues, and immunohistochemistry was used to test the protein expression in breast cancer tissues and adjacent tissues. In addition, an adenovirus vector system was utilized to upregulate the expression of PHF2 in breast cancer cells. In our study, we found that PHF2 was down-expressed in breast cancer on both the mRNA and protein levels and the low expression of PHF2 was significantly associated with lymph node metastasis, Ki67 positive rate, ER negative expression and poor prognosis in breast cancer patients. The ectopic expression of PHF2 obviously inhibited the proliferation of breast cancer cell lines and the growth of xenograft tumors. Due to the tumor suppressor signature of PHF2 in breast cancer, we have reasons to believe that it could be a promoting marker and target for the prognosis and therapy of breast cancer.

V144D Mutation of SPTLC1 Can Present with Both Painful and Painless Phenotypes in Hereditary Sensory and Autonomic Neuropathies Type I

Hereditary sensory and autonomic neuropathy type I (HSAN I) is an autosomal dominant disease characterized by distal sensory loss, pain insensitivity, and autonomic disturbances. The major underlying causes of HSAN I are point mutations in the SPTLC1 gene. Patients with mutations in the SPTLC1 genes typically exhibit dense sensory loss and incidence of lancinating pain. Although most of these mutations produce sensory loss, it is unclear which mutations would lead to the painful phenotype. In this case series, we report that the V144D mutation in SPTLC1 gene may relate to both painful and painless peripheral neuropathies. The unique clinical phenotype of this mutation may guide clinical workup and treatment for patients with painful and painless neuropathies.

Hereditary sensory neuropathy type 1-associated deoxysphingolipids cause neurotoxicity, acute calcium handling abnormalities and mitochondrial dysfunction in vitro

Hereditary sensory neuropathy type 1 (HSN-1) is a peripheral neuropathy most frequently caused by mutations in the SPTLC1 or SPTLC2 genes, which code for two subunits of the enzyme serine palmitoyltransferase (SPT). SPT catalyzes the first step of de novo sphingolipid synthesis. Mutations in SPT result in a change in enzyme substrate specificity, which causes the production of atypical deoxysphinganine and deoxymethylsphinganine, rather than the normal enzyme product, sphinganine. Levels of these abnormal compounds are elevated in blood of HSN-1 patients and this is thought to cause the peripheral motor and sensory nerve damage that is characteristic of the disease, by a largely unresolved mechanism. In this study, we show that exogenous application of these deoxysphingoid bases causes dose- and time-dependent neurotoxicity in primary mammalian neurons, as determined by analysis of cell survival and neurite length. Acutely, deoxysphingoid base neurotoxicity manifests in abnormal Ca2+ handling by the endoplasmic reticulum (ER) and mitochondria as well as dysregulation of cell membrane store-operated Ca2+ channels. The changes in intracellular Ca2+ handling are accompanied by an early loss of mitochondrial membrane potential in deoxysphingoid base-treated motor and sensory neurons. Thus, these results suggest that exogenous deoxysphingoid base application causes neuronal mitochondrial dysfunction and Ca2+ handling deficits, which may play a critical role in the pathogenesis of HSN-1.

HSAN1 mutations in serine palmitoyltransferase reveal a close structure-function-phenotype relationship

Hereditary sensory and autonomic neuropathy type 1 (HSAN1) is a rare autosomal dominant inherited peripheral neuropathy caused by mutations in the SPTLC1 and SPTLC2 subunits of serine palmitoyltransferase (SPT). The mutations induce a permanent shift in the substrate preference from L-serine to L-alanine, which results in the pathological formation of atypical and neurotoxic 1-deoxy-sphingolipids (1-deoxySL). Here we compared the enzymatic properties of 11 SPTLC1 and six SPTLC2 mutants using a uniform isotope labelling approach. In total, eight SPT mutants (STPLC1p.C133W, p.C133Y, p.S331F, p.S331Y and SPTLC2p.A182P, p.G382V, p.S384F, p.I504F) were associated with increased 1-deoxySL synthesis. Despite earlier reports, canonical activity with l-serine was not reduced in any of the investigated SPT mutants. Three variants (SPTLC1p.S331F/Y and SPTLC2p.I505Y) showed an increased canonical activity and increased formation of C20 sphingoid bases. These three mutations are associated with an exceptionally severe HSAN1 phenotype, and increased C20 sphingosine levels were also confirmed in plasma of patients. A principal component analysis of the analysed sphingoid bases clustered the mutations into three separate entities. Each cluster was related to a distinct clinical outcome (no, mild and severe HSAN1 phenotype). A homology model based on the protein structure of the prokaryotic SPT recapitulated the same grouping on a structural level. Mutations associated with the mild form clustered around the active site, whereas mutations associated with the severe form were located on the surface of the protein. In conclusion, we showed that HSAN1 mutations in SPT have distinct biochemical properties, which allowed for the prediction of the clinical symptoms on the basis of the plasma sphingoid base profile.

Epigenetic regulation of adipogenesis by PHF2 histone demethylase

PHF2 is a JmjC family histone demethylase that removes the methyl group from H3K9me2 and works as a coactivator for several metabolism-related transcription factors. In this study, we examined the in vivo role of PHF2 in mice. We generated Phf2 floxed mice, systemic Phf2 null mice by crossing Phf2 floxed mice with CMV-Cre transgenic mice, and tamoxifen-inducible Phf2 knockout mice by crossing Phf2 floxed mice with Cre-ERT2 transgenic mice. Systemic Phf2 null mice had partial neonatal death and growth retardation and exhibited less adipose tissue and reduced adipocyte numbers compared with control littermates. Tamoxifen-induced conditional knockout of PHF2 resulted in impaired adipogenesis in stromal vascular cells from the adipose tissue of tamoxifen-inducible Phf2 knockout mice as well as of Phf2 knocked-down 3T3-L1 cells. PHF2 interacts with CEBPA and demethylates H3K9me2 in the promoters of CEBPA-regulated adipogenic genes. These findings suggest that PHF2 histone demethylase potentiates adipogenesis through interaction with CEBPA in vivo. Taken together, PHF2 may be a novel therapeutic target in the treatment of obesity and the metabolic syndrome.

Genes, molecules and patients--emerging topics to guide clinical pain research

This review selectively explores some areas of pain research that, until recently, have been poorly understood. We have chosen four topics that relate to clinical pain and we discuss the underlying mechanisms and related pathophysiologies contributing to these pain states. A key issue in pain medicine involves crucial events and mediators that contribute to normal and abnormal pain signaling, but remain unseen without genetic, biomarker or imaging analysis. Here we consider how the altered genetic make-up of familial pains reveals the human importance of channels discovered by preclinical research, followed by the contribution of receptors as stimulus transducers in cold sensing and cold pain. Finally we review recent data on the neuro-immune interactions in chronic pain and the potential targets for treatment in cancer-induced bone pain.

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.

Overexpression of Jumonji AT-rich interactive domain 1B and PHD finger protein 2 is involved in the progression of esophageal squamous cell carcinoma

Jumonji AT-rich interactive domain 1B (JARID1B) and PHD finger protein 2 (PHF2), members of the histone demethylases, have been found to be involved in many types of tumors. However, the expression and prognostic significance of JARID1B and PHF2 in esophageal squamous cell carcinoma (ESCC) still remains unclear. In this study, JARID1B and PHF2 expression were detected on tissue microarrays of ESCC samples in 120 cases using immunohistochemical staining. Our results showed that JARID1B and PHF2 were overexpressed in ESCCs. In addition, a significant correlation was observed between JARID1B nuclear expression level and histological grade (P=0.003). Kaplan-Meier survival analysis showed a tendency that high cytoplasmic expression of JARID1B and PHF2 was associated with decreased overall survival of ESCC patients, whereas JARID1B high expression in the nucleus was associated with high overall survival, although there was no statistical significance. Overall, our data suggest that JARID1B and PHF2 are overexpressed in ESCC and that they may play crucial roles in the course of ESCC initiation and/or progression.

A case of Bureau-Barrie`re-type sporadic ulcerative-mutilatingacropathy

A rare clinical case of Bureau-Barrie`re-type sporadic ulcerative-mutilating acropathy is described.

Lack of collagen XV impairs peripheral nerve maturation and, when combined with laminin-411 deficiency, leads to basement membrane abnormalities and sensorimotor dysfunction

Although the Schwann cell basement membrane (BM) is required for normal Schwann cell terminal differentiation, the role of BM-associated collagens in peripheral nerve maturation is poorly understood. Collagen XV is a BM zone component strongly expressed in peripheral nerves, and we show that its absence in mice leads to loosely packed axons in C-fibers and polyaxonal myelination. The simultaneous lack of collagen XV and another peripheral nerve component affecting myelination, laminin α4, leads to severely impaired radial sorting and myelination, and the maturation of the nerve is permanently compromised, contrasting with the slow repair observed in Lama4-/- single knock-out mice. Moreover, the Col15a1-/-;Lama4-/- double knock-out (DKO) mice initially lack C-fibers and, even over 1 year of age have only a few, abnormal C-fibers. The Lama4-/- knock-out results in motor and tactile sensory impairment, which is exacerbated by a simultaneous Col15a1-/- knock-out, whereas sensitivity to heat-induced pain is increased in the DKO mice. Lack of collagen XV results in slower sensory nerve conduction, whereas the Lama4-/- and DKO mice exhibit increased sensory nerve action potentials and decreased compound muscle action potentials; x-ray diffraction revealed less mature myelin in the sciatic nerves of the latter than in controls. Ultrastructural analyses revealed changes in the Schwann cell BM in all three mutants, ranging from severe (DKO) to nearly normal (Col15a1-/-). Collagen XV thus contributes to peripheral nerve maturation and C-fiber formation, and its simultaneous deletion from neural BM zones with laminin α4 leads to a DKO phenotype distinct from those of both single knock-outs.

The genetics of pain: implications for evaluation and treatment of spinal disease

BACKGROUND CONTEXT

Variability in human pain experience appears to be at least partially determined by genetic inheritance. To the extent that awareness of individual pain sensitivity and the tendency to develop chronic pain after injury or surgery would be informative for clinical decision making, development and use of genetic testing for specific pain markers could contribute to improved outcomes in management of spinal disease.

PURPOSE

To review important and illustrative results from both classical and modern pain genetics studies and to introduce readers to critical definitions and concepts necessary to interpret the growing body of genetics literature relevant to spinal disease.

STUDY DESIGN/SETTING

Literature review and commentary.

METHODS

A review was performed of published English language studies in which genetic techniques were used to analyze the molecular basis of nociceptive signaling or processing with a particular emphasis on studies addressing genetic determinants of interindividual variability in pain sensitivity or predisposition to chronic pain.

RESULTS

There is compelling evidence indicating that interindividual differences in pain sensitivity and the risk of developing chronic pain syndromes are genetically determined. Despite a growing list of putative "pain genes," genetic association studies remain plagued with difficulty replicating initial findings in different cohorts.

CONCLUSIONS

Genome-wide association studies are potentially powerful means of identifying clinically relevant genetic markers predicting disease susceptibility, severity, and treatment response. However, accurate results require rigorous study design with use of large homogeneous populations and precise phenotypes.

Thermosensory and mechanosensory perception in human genetic disease

Peripheral sensory perception is established through an elaborate network of specialized neurons that mediate the translation of extraorganismal stimuli through the use of a broad array of receptors and downstream effector molecules. Studies of human genetic disorders, as well as mouse and other animal models, have identified some of the key molecules necessary for peripheral innervation and function. These findings have, in turn, yielded new insights into the developmental networks and homeostatic mechanisms necessary for the transformation of external stimuli into interpretable electrical impulses. In this review, we will summarize and discuss some of the genes/proteins implicated in two particular aspects of sensory perception, thermosensation and mechanosensation, highlighting pathways whose perturbation leads to both isolated and syndromic sensory deficits.

The external aldimine form of serine palmitoyltransferase: structural, kinetic, and spectroscopic analysis of the wild-type enzyme and HSAN1 mutant mimics

Sphingolipid biosynthesis begins with the condensation of L-serine and palmitoyl-CoA catalyzed by the PLP-dependent enzyme serine palmitoyltransferase (SPT). Mutations in human SPT cause hereditary sensory autonomic neuropathy type 1, a disease characterized by loss of feeling in extremities and severe pain. The human enzyme is a membrane-bound hetereodimer, and the most common mutations are located in the enzymatically incompetent monomer, suggesting a "dominant" or regulatory effect. The molecular basis of how these mutations perturb SPT activity is subtle and is not simply loss of activity. To further explore the structure and mechanism of SPT, we have studied the homodimeric bacterial enzyme from Sphingomonas paucimobilis. We have analyzed two mutants (N100Y and N100W) engineered to mimic the mutations seen in hereditary sensory autonomic neuropathy type 1 as well as a third mutant N100C designed to mimic the wild-type human SPT. The N100C mutant appears fully active, whereas both N100Y and N100W are significantly compromised. The structures of the holoenzymes reveal differences around the active site and in neighboring secondary structure that transmit across the dimeric interface in both N100Y and N100W. Comparison of the l-Ser external aldimine structures of both native and N100Y reveals significant differences that hinder the movement of a catalytically important Arg(378) residue into the active site. Spectroscopic analysis confirms that both N100Y and N100W mutants subtly affect the chemistry of the PLP. Furthermore, the N100Y and R378A mutants appear less able to stabilize a quinonoid intermediate. These data provide the first experimental insight into how the most common disease-associated mutations of human SPT may lead to perturbation of enzyme activity.

Identification of small subunits of mammalian serine palmitoyltransferase that confer distinct acyl-CoA substrate specificities

Serine palmitoyltransferase (SPT) catalyzes the first committed step in sphingolipid biosynthesis. In yeast, SPT is composed of a heterodimer of 2 highly-related subunits, Lcb1p and Lcb2p, and a third subunit, Tsc3p, which increases enzyme activity markedly and is required for growth at elevated temperatures. Higher eukaryotic orthologs of Lcb1p and Lcb2p have been identified, but SPT activity is not highly correlated with coexpression of these subunits and no ortholog of Tsc3p has been identified. Here, we report the discovery of 2 proteins, ssSPTa and ssSPTb, which despite sharing no homology with Tsc3p, each substantially enhance the activity of mammalian SPT expressed in either yeast or mammalian cells and therefore define an evolutionarily conserved family of low molecular weight proteins that confer full enzyme activity. The 2 ssSPT isoforms share a conserved hydrophobic central domain predicted to reside in the membrane, and each interacts with both hLCB1 and hLCB2 as assessed by positive split ubiquitin 2-hybrid analysis. The presence of these small subunits, along with 2 hLCB2 isofoms, suggests that there are 4 distinct human SPT isozymes. When each SPT isozyme was expressed in either yeast or CHO LyB cells lacking endogenous SPT activity, characterization of their in vitro enzymatic activities, and long-chain base (LCB) profiling revealed differences in acyl-CoA preference that offer a potential explanation for the observed diversity of LCB seen in mammalian cells.

Mutilating acral ulcers: the spectrum of differential diagnosis

Prominent acral mutilating ulcers can be present in sensorimotor neuropathies. Although diabetes mellitus is the most common cause of neuropathic ulcers, these skin lesions may manifest in nondiabetic neuropathies. The dermatologic abnormalities may even precede the onset of typical neuropathic symptoms, leading to diagnostic confusion. Therefore, a broad differential diagnosis of neurological and systemic disorders should be considered when evaluating patients who have acral skin ulcerations. We report 3 cases of mutilating ulcers associated with nondiabetic neuropathies. The first case is a woman with multiple ulcerations on her forearm, hands, and toes. Her nerve biopsy revealed neuropathy with multiple congophilic deposits consistent with amyloid neuropathy. The second case is a woman with necrotic painless ulcer on her heel. Nerve biopsy in this patient revealed features suggestive of vasculitic neuropathy. The third case is a man with multiple ulcers on his extremities. A sural nerve biopsy in this patient was consistent with leprous neuropathy.

Erasing the methyl mark: histone demethylases at the center of cellular differentiation and disease

The enzymes catalyzing lysine and arginine methylation of histones are essential for maintaining transcriptional programs and determining cell fate and identity. Until recently, histone methylation was regarded irreversible. However, within the last few years, several families of histone demethylases erasing methyl marks associated with gene repression or activation have been identified, underscoring the plasticity and dynamic nature of histone methylation. Recent discoveries have revealed that histone demethylases take part in large multiprotein complexes synergizing with histone deacetylases, histone methyltransferases, and nuclear receptors to control developmental and transcriptional programs. Here we review the emerging biochemical and biological functions of the histone demethylases and discuss their potential involvement in human diseases, including cancer.

Hereditary sensory neuropathy type I

Hereditary sensory neuropathy type I (HSN I) is a slowly progressive neurological disorder characterised by prominent predominantly distal sensory loss, autonomic disturbances, autosomal dominant inheritance, and juvenile or adulthood disease onset. The exact prevalence is unknown, but is estimated as very low. Disease onset varies between the 2^nd and 5^th decade of life. The main clinical feature of HSN I is the reduction of sensation sense mainly distributed to the distal parts of the upper and lower limbs. Variable distal muscle weakness and wasting, and chronic skin ulcers are characteristic. Autonomic features (usually sweating disturbances) are invariably observed. Serious and common complications are spontaneous fractures, osteomyelitis and necrosis, as well as neuropathic arthropathy which may even necessitate amputations. Some patients suffer from severe pain attacks. Hypacusis or deafness, or cough and gastrooesophageal reflux have been observed in rare cases. HSN I is a genetically heterogenous condition with three loci and mutations in two genes (SPTLC1 and RAB7) identified so far. Diagnosis is based on the clinical observation and is supported by a family history. Nerve conduction studies confirm a sensory and motor neuropathy predominantly affecting the lower limbs. Radiological studies, including magnetic resonance imaging, are useful when bone infections or necrosis are suspected. Definitive diagnosis is based on the detection of mutations by direct sequencing of the SPTLC1 and RAB7 genes. Correct clinical assessment and genetic confirmation of the diagnosis are important for appropriate genetic counselling and prognosis. Differential diagnosis includes the other hereditary sensory and autonomic neuropathies (HSAN), especially HSAN II, as well as diabetic foot syndrome, alcoholic neuropathy, neuropathies caused by other neurotoxins/drugs, immune mediated neuropathy, amyloidosis, spinal cord diseases, tabes dorsalis, lepra neuropathy, or decaying skin tumours like amelanotic melanoma. Management of HSN I follows the guidelines given for diabetic foot care (removal of pressure to the ulcer and eradication of infection, followed by the use of specific protective footwear) and starts with early and accurate counselling of patients about risk factors for developing foot ulcerations. The disorder is slowly progressive and does not influence life expectancy but is often severely disabling after a long duration of the disease.

Roles of l-serine and sphingolipid synthesis in brain development and neuronal survival

Sphingolipids represent a class of membrane lipids that contain a hydrophobic ceramide chain as its common backbone structure. Sphingolipid synthesis requires two simple components: l-serine and palmitoyl CoA. Although l-serine is classified as a non-essential amino acid, an external supply of l-serine is essential for the synthesis of sphingolipids and phosphatidylserine (PS) in particular types of central nervous system (CNS) neurons. l-Serine is also essential for these neurons to undergo neuritogenesis and to survive. Biochemical analysis has shown that l-serine is synthesized from glucose and released by astrocytes but not by neurons, which is the major reason why this amino acid is an essential amino acid for neurons. Biosynthesis of membrane lipids, such as sphingolipids, PS, and phosphatidylethanolamine (PE), in neurons is completely dependent on this astrocytic factor. Recent advances in lipid biology research using transgenic mice have demonstrated that synthesis of endogenous l-serine and neuronal sphingolipids is essential for brain development. In this review, we discuss the metabolic system that coordinates sphingolipid synthesis with the l-serine synthetic pathway between neurons and glia. We also discuss the crucial roles of the metabolic conversion of l-serine to sphingolipids in neuronal development and survival. Human diseases associated with serine and sphingolipid biosynthesis are also discussed.

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.

Hereditary sensory and autonomic neuropathy type I in a Chinese family: British C133W mutation exists in the Chinese

Hereditary sensory and autonomic neuropathy type I (HSAN I) is an autosomal dominant disorder of the peripheral nervous system characterized by marked progressive sensory loss, with variable autonomic and motor involvement. The HSAN I locus maps to chromosome 9q22.1-22.3 and is caused by mutations in the gene coding for serine palmitoyltransferase long chain base subunit 1 (SPTLC1). Sequencing in HSAN I families have previously identified mutations in exons 5, 6 and 13 of this gene. Here we report the clinical, electrophysiological and pathological findings of a proband in a Chinese family with HSAN I. The affected members showed almost typical clinical features. Electrophysiological findings showed an axonal, predominantly sensory, neuropathy with motor and autonomic involvement. Sural nerve biopsy showed loss of myelinated and unmyelinated fibers. SPTLC1 mutational analysis revealed the C133W mutation, a mutation common in British HSAN I families.

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.

Small-fiber neuropathy: answering the burning questions

Small-fiber neuropathy is a peripheral nerve disease that most commonly presents in middle-aged and older people, who develop burning pain in their feet. Although it can be caused by disorders of metabolism such as diabetes, chronic infections (such as with human immunodeficiency virus), genetic abnormalities, toxicity from various drugs, and autoimmune diseases, the cause often remains a mystery because standard electrophysiologic tests for nerve injury do not detect small-fiber function. Inadequate ability to test for and diagnose small-fiber neuropathies has impeded patient care and research, but new tools offer promise. Infrequently, the underlying cause of small-fiber dysfunction is identified and disease-modifying therapy can be instituted. More commonly, the treatments for small-fiber neuropathy involve symptomatic treatment of neuropathic pain.

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.

Autosomal dominant hereditary sensory neuropathy with chronic cough and gastro-oesophageal reflux: clinical features in two families linked to chromosome 3p22-p24

Autosomal dominant hereditary sensory neuropathy (HSN I) is a clinically and genetically heterogeneous group of disorders, and in some families it is due to mutations in the serine palmitoyltransferase (SPTLC1) gene. We have characterized two families with HSN I associated with cough and gastro-oesophageal reflux (GOR). From a large Australian family, 27 individuals and from a smaller family, 11 individuals provided clinical information and blood for genetic analysis. Affected individuals had an adult onset of paroxysmal cough, GOR and distal sensory loss. Cough could be triggered by noxious odours or by pressure in the external auditory canal (Arnold's ear-cough reflex). Other features included throat clearing, hoarse voice, cough syncope and sensorineural hearing loss. Neurophysiological and pathological studies demonstrated a sensory axonal neuropathy. Gastric emptying studies were normal, and autonomic function and sweat tests were either normal or showed distal hypohidrosis. Cough was likely to be due to a combination of denervation hypersensitivity of the upper airways and oesophagus, and prominent GOR. Most affected individuals were shown on 24 h ambulatory oesophageal pH monitoring to have multiple episodes of GOR, closely temporally associated with coughing. Hoarse voice was probably attributable to acid-induced laryngeal damage, and there was no evidence of vocal cord palsy. No other cause for cough was found on most respiratory or otorhinological studies. Linkage to chromosome 3p22-p24 has been found in both families, with no evidence of linkage to loci for known HSN I, autosomal dominant hereditary motor and sensory neuropathy, hereditary GOR or triple A syndrome. These families represent a genetically novel variant of HSN I, with a distinctive cough owing to involvement of the upper aerodigestive tract.

Congenital insensitivity to pain—review and report of a case with dental implications

Pain is a protective mechanism for the body. Absence of pain is a symptom in several disorders, both congenital and acquired. The congenital types are present at birth and affect the number and distribution of types of nerve fibers. At present, 5 types of hereditary sensory and autonomic neuropathies have been identified. The various disorders within this group are classified according to the different patterns of sensory and autonomic dysfunction and peripheral neuropathy and the presence of additional clinical features such as learning disability. However, the field is currently moving away from classification based on clinical presentation toward classification based on underlying genetic abnormality. In the absence of pain, patients are at risk of late presentation with illnesses or injuries, and have an increased incidence of traumatic injury. Self-mutilation is an almost invariable feature of these disorders. We report the case of a patient with congenital insensitivity to pain that presented with self-mutilation injuries to his hands and oral tissues caused by biting. The severe nature of these injuries necessitated serial extraction of his primary teeth soon after eruption, which led to a cessation of the problem. The mutilation has not returned following the eruption of the first of his permanent teeth, suggesting that he has learned not to bite himself, even though to do so causes him no discomfort.

Clinical, pathological and genetic characterization of hereditary sensory and autonomic neuropathy type 1 (HSAN I)

Hereditary sensory and autonomic neuropathy type I (HSAN I) is the most frequent type of hereditary neuropathy that primarily affects sensory neurons. The genetic locus for HSAN I has been mapped to chromosome 9q22.1-22.3 and recently the gene was identified as SPTLC1, encoding serine palmitoyltransferase, long chain base subunit-1. Sequencing in HSAN I families have previously identified mutations in exons 5, 6 and 13 of this gene. We analysed the SPTLC1 gene for mutations in 8 families with HSAN I, 60 individuals with sporadic sensory neuropathy, 6 HSAN II families, 20 Charcot-Marie-Tooth type I families and 20 families with Charcot-Marie-Tooth type II. Six HSAN I families and a single sporadic neuropathy case had an identical SPTLC1 mutation. No mutations were found in the other groups. Genetic haplotyping across the HSAN I critical region in 5 families and the sporadic case suggested a common founder. Several characteristics, previously not widely recognized were identified, including lack of penetrance of the SPTLC1 mutation in some individuals, variability in age of onset along with an earlier age of onset in younger generations, in some patients surprisingly early and often severe motor involvement and an earlier onset characterized by motor involvement with demyelinating features in males compared to females in 4 families. The sensory findings were often disassociated with prominent pain and temperature loss. Neurophysiology mainly showed a sensory axonal neuropathy but in many individuals there was electrical evidence of demyelination. Sural nerve biopsies from six affected individuals and the post-mortem findings in 1 case showed mainly axonal loss. This in depth study on the phenotype of HSAN I in 6 families and a single sporadic case with a common founder identifies a number of poorly recognized features in this disorder and highlights the clinical heterogeneity both within and between families suggesting the influence of other genetic and acquired factors.

Late-onset hereditary sensory neuropathy type I due to SPTLC1 mutation: autopsy findings

There is little published information on the autopsy findings in hereditary sensory neuropathy type I (HSN I), and none in genetically confirmed cases. We report the neuropathological findings in a 93-year-old woman with a disease of unusually late onset, who was part of a large HSN I kindred and in whom genetic analysis confirmed an SPTLC1 T399G mutation.

Charcot-Marie-Tooth disease (hereditary motor sensory neuropathies) and hereditary sensory and autonomic neuropathies

BACKGROUND

Since the description of Charcot-Marie-Tooth disease over a century ago. it has now been recognized that these conditions are not caused by generalized metabolic defects but rather have various discrete genetic origins. These disorders can also have variable phenotypes due to dysfunction of peripheral nerve axons or their myelin due to the genetic defects that affect the formation of specific nerve proteins.

REVIEW SUMMARY

This article summarizes the clinical presentation of various phenotypes of the hereditary motor sensory neuropathies and the hereditary sensory and autonomic neuropathies, genetic mutations, and their relevant protein products. Proper identification of the genetic defects provides the opportunity for better genetic counseling and hopefully therapies in the future.

Hereditary sensory neuropathy type 1 in a Portuguese family-electrodiagnostic and autonomic nervous system studies

Hereditary sensory and autonomic neuropathy type 1 (HSAN 1) is a dominantly inherited disorder; its gene locus is mapped on chromosome 9q22. Three different missense mutations (C133Y, C133W and V144D) have been described in 11 families from Australia, England and Austria. Common clinical features have been found in these families. We report the clinical and electrophysiological features of three members of a large Portuguese family with HSAN 1 and the C133Y missense mutation. The affected members showed typical clinical features. Electrophysiological findings were consistent with a distal axonal predominantly sensory neuropathy with motor involvement, in three different severity stages. No autonomic involvement was detected in sudomotor and cardiovascular tests. This report documents the lesion of the motor nerve fibers in this disease, as well as the preservation of the autonomic nervous system function, therefore suggesting that HSNA is an inappropriate name for this disorder.

Inflammatory glial activation in the brain of a patient with hereditary sensory neuropathy type 1 with deafness and dementia

The brain of a patient with hereditary sensory neuropathy type 1 (HSN-1) associated with sensorineural deafness and early-onset dementia was neuropathologically investigated. Widespread neuronal degeneration in cerebral neocortex, hippocampus and basal ganglia was revealed, accounting for the clinical features. Loss of neurons with ballooning of residual neurons was remarkable in the hippocampus and frontal, parietal, and occipital lobes. Neuronal degeneration in these regions was accompanied by axonal dystrophy and glial reactions such as microgliosis and astrocytosis, however, only glial responses were prominent in the basal ganglia, brain-stem and cerebellum with mild neuronal loss. These results indicate that the widespread neuronal degeneration may be accelerated by inflammatory processes including glial activation in the brain of a patient with HSN-1 associated with deafness and dementia.

A novel RAB7 mutation associated with ulcero-mutilating neuropathy

There are two known autosomal dominant genes for the hereditary ulcero-mutilating neuropathies: SPTLC1 (hereditary sensory neuropathy type 1) and RAB7 (Charcot-Marie-Tooth disease type 2B). We report a family with autosomal dominant ulcero-mutilating neuropathy, developing in the teens and characterized by ulcers, amputations, sensory involvement in the feet but no motor features. Sequencing the RAB7 gene showed a novel heterozygous A to C mutation, changing asparagine to threonine at codon 161. The mutation is situated adjacent to a previously identified valine to methionine mutation at codon 162, implying a hotspot for mutations in the highly conserved C terminus of RAB7.

A mutation in the HSN2 gene causes sensory neuropathy type II in a Lebanese family

Hereditary sensory and autonomic neuropathy (HSAN) type II is an autosomal recessive disorder clinically characterized by distal and proximal sensory loss that is caused by the reduction or absence of peripheral sensory nerves. Recently, a novel gene called HSN2 has been found to be the cause of HSAN type II in five families from Newfoundland and Quebec. Screening of this gene in an HSAN type II Lebanese family showed a 1bp deletion mutation found in a homozygous state in all affected individuals. This novel mutation supports the hypothesis that HSN2 is the causative gene for HSAN type II.

Hereditary sensory neuropathies

PURPOSE OF REVIEW

The hereditary sensory neuropathies, also known as the hereditary sensory and autonomic neuropathies, are a clinically and genetically heterogeneous group of disorders. As they are not as common as Charcot-Marie-Tooth disease, they do not receive the same level of attention, but there have been major advances in the identification of the causative genes in the past decade. Certain forms of hereditary sensory and autonomic neuropathy, especially hereditary sensory and autonomic neuropathy type I, which has minimal autonomic involvement and is more accurately termed hereditary sensory neuropathy type I, can present in a very similar fashion to certain forms of Charcot-Marie-Tooth disease (Charcot-Marie-Tooth type 2B, see below), and therefore it is important that clinicians who regularly manage patients with neuropathy are familiar with the latest developments in the hereditary sensory and autonomic neuropathies. This review will concentrate on the recent genetic advances in hereditary sensory and autonomic neuropathy, and especially on those forms that overlap clinically with Charcot-Marie-Tooth disease, hence the title of the review 'Hereditary sensory neuropathies' rather than hereditary sensory and autonomic neuropathies.

Persistent Pain as a Disease Entity: Implications for Clinical Management

Pain has often been regarded merely as a symptom that serves as a passive warning signal of an underlying disease process. Using this model, the goal of treatment has been to identify and address the pathology causing pain in the expectation that this would lead to its resolution. However, there is accumulating evidence to indicate that persistent pain cannot be regarded as a passive symptom. Continuing nociceptive inputs result in a multitude of consequences that impact on the individual, ranging from changes in receptor function to mood dysfunction, inappropriate cognitions, and social disruption. These changes that occur as a consequence of continuing nociceptive inputs argue for the consideration of persistent pain as a disease entity in its own right. As with any disease, the extent of these changes is largely determined by the internal and external environments in which they occur. Thus genetic, psychological and social factors may all contribute to the perception and expression of persistent pain. Optimal outcomes in the management of persistent pain may be achieved not simply by attempting to remove the cause of the pain, but by addressing both the consequences and contributors that together comprise the disease of persistent pain.

Transcript map of the candidate region for HSNI with cough and gastroesophageal reflux on chromosome 3p and exclusion of candidate genes

Dominantly inherited sensory neuropathy (HSNI) is a degenerative disorder of sensory neurons characterized predominantly by sensory loss with mild motor impairment. Recently our group identified a locus on chromosome 3p for a new form of HSNI associated with cough and gastroesophageal reflux (GER). Haplotype analysis in a second family refined the interval to a 3.4-cM region that includes the candidate genes TOP2B and SLC4A7. The genes TOP2B and SLC4A7 and five other characterized genes that map within the critical interval have been investigated and excluded from having a pathogenic role in HSNI with cough and GER. Two novel single nucleotide polymorphisms were identified; however both changes were observed in affected and non-affected individuals, suggesting that they have no relation to the disease. We have used the resources of the Human Genome Project to report a transcript map of the region on chromosome 3p24 containing the HSNI with cough and GER locus.

Structural, psychological, and genetic influences on low back and neck pain: a study of adult female twins

OBJECTIVE

To assess genetic and environmental influences on low back and neck pain in a classic twin design and to examine the extent to which these are explained by structural changes seen on magnetic resonance imaging (MRI) and psychological and lifestyle variables.

METHODS

The subjects comprised 1,064 unselected women (181 monozygotic [MZ] and 351 dizygotic [DZ] twin pairs) recruited from a national registry of twin volunteers. Outcome measures included lifetime history of low back and neck pain (using a range of increasingly stringent definitions), MRI scores of disc degeneration in the lumbar and cervical spine, psychological distress as assessed by the General Health Questionnaire (GHQ), and lifestyle variables assessed by questionnaire.

RESULTS

For all definitions of pain, there was a consistent excess concordance in MZ when compared with DZ twins, equating to a heritability for low back pain in the range of 52-68% and for neck pain in the range of 35-58%. The strongest associations were between low back pain and MRI change (odds ratio [OR] 3.6, 95% confidence interval [95% CI] 1.8-7.3]) and between neck pain and response on the GHQ (OR 3.3, 95% CI 2.1-5.0). These associations were mediated genetically.

CONCLUSIONS

Genetic factors have an important influence on back and neck pain reporting in women. These factors include the genetic determinants of structural disc degeneration and an individual's inherited tendency toward psychological distress. MRI changes are the strongest predictor of low back pain.

Activity of partially inhibited serine palmitoyltransferase is sufficient for normal sphingolipid metabolism and viability of HSN1 patient cells

Hereditary sensory neuropathy type I (HSN1) is a common degenerative disorder of peripheral sensory neurons. HSN1 is caused by mutations in the gene, encoding the long chain base 1 of serine palmitoyltransferase (SPT) [Nat. Genet. 27 (2001) 309]. Here, we show a 44% reduction of SPT activity in transformed lymphocytes from HSN1 patients with mutation T399G in the SPTLC1 gene. However, the decrease in SPT activity had no effect on de novo sphingolipid biosynthesis, cellular sphingolipid content, cell proliferation and death (apoptosis and necrosis). The removal of extracellular sphingolipids did not affect viability of HSN1 cells. We also found no significant difference in whole blood counts, viability, and permeability to Triton X-100 of primary lymphocytes from HSN1 patients. These results suggest that, despite the inhibition of mutant allele, the activity of nonmutant allele of STP may be sufficient for adequate sphingolipid biosynthesis and cell viability. Therefore, the neurodegeneration in HSN1 is likely to be caused by subtler and rather long-term effect(s) of these mutations such as loss of a cell-type selective facet of sphingolipid metabolism and/or function, or perhaps accumulation of toxic species, including abnormal protein(s) as in other neurodegenerations.

Hereditary neuropathies

The spectrum of hereditary neuropathies has evolved recently as a result of the exponential growth of genetic research. For the purpose of this review, we will use Charcot-Marie-Tooth (CMT), hereditary liability to pressure palsy (HNPP) and hereditary sensory and autonomic neuropathies (HSAN) to illustrate the current clinical and genetic approach to such neuropathies.

A locus for hereditary sensory neuropathy with cough and gastroesophageal reflux on chromosome 3p22-p24

Hereditary sensory neuropathy type I (HSN I) is a group of dominantly inherited degenerative disorders of peripheral nerve in which sensory features are more prominent than motor involvement. We have described a new form of HSN I that is associated with cough and gastroesophageal reflux. To map the chromosomal location of the gene causing the disorder, a 10-cM genome screen was undertaken in a large Australian family. Two-point analysis showed linkage to chromosome 3p22-p24 (Zmax=3.51 at recombination fraction (theta) 0.0 for marker D3S2338). A second family with a similar phenotype shares a different disease haplotype but segregates at the same locus. Extended haplotype analysis has refined the region to a 3.42-cM interval, flanked by markers D3S2336 and D3S1266.

Terminal changes in hereditary sensory and autonomic neuropathy: a long-term follow-up of a sporadic case

We describe terminal changes in a long-term follow-up of a 51-year-old man with sporadic hereditary sensory and autonomic neuropathy (HSAN). From the age of 15 years onwards, he suffered from multiple painless ulcers of his feet and fingers, necessitating amputation. Neurological studies revealed almost complete sensory loss affecting all modalities in the upper and lower limbs, minimal involvement of motor fibers, and areflexia. A neurophysiological abnormality involved an absence of sensory action potentials with relatively normal motor nerve conduction velocities. Biopsy of the sural nerve showed almost total loss of myelinated fibers with a mild decrease in unmyelinated fibers. Despite the late onset of the disease, the progressive course, and the lancinating pain, the terminal features of this patient, which involved a selective loss of myelinated fibers and widespread sensory loss, seem to be symptomatic of HSAN II, the progressive form of autosomal recessive sensory neuropathy, and emphasize the clinical heterogeneity of HSAN.

Hereditary sensory neuropathy type 1 mutations confer dominant negative effects on serine palmitoyltransferase, critical for sphingolipid synthesis

Hereditary sensory neuropathy type 1 (HSN1) is a dominantly inherited degenerative disorder of the peripheral nerves. HSN1 is clinically and genetically heterogeneous. One form arises from mutations in the gene SPTLC1 encoding long-chain base 1 (LCB1), one of two subunits of serine palmitoyltransferase (SPT), the enzyme catalyzing the initial step of sphingolipid synthesis. We have examined the effects of the mutations C133Y and C133W, which we have identified in two HSN1 families, on the function of SPT. Although in HSN1 lymphoblasts, the C133Y and C133W mutations do not alter the steady-state levels of LCB1 and LCB2 subunits, they result in reduced SPT activity and sphingolipid synthesis. Moreover, in a mutant Chinese hamster ovary (CHO) cell strain with defective SPT activity due to a lack of the LCB1 subunit, these mutations impair the ability of the LCB1 subunit to complement the SPT deficiency. Furthermore, the overproduction of either the LCB1C133Y or LCB1C133W subunit inhibits SPT activity in CHO cells despite the presence of wild-type LCB1. In addition, we demonstrate that in CHO cells the mutant LCB1 proteins, similar to the normal LCB1, can interact with the wild-type LCB2 subunit. These results indicate that the HSN1-associated mutations in LCB1 confer dominant negative effects on the SPT enzyme.

Exclusion of serine palmitoyltransferase long chain base subunit 2 (SPTLC2) as a common cause for hereditary sensory neuropathy

Recently point mutations in the SPTLC1 subunit of serine palmitoyltransferase have been shown to cause the common form of dominant hereditary sensory neuropathy (HSN1). Serine palmitoyltransferase (SPT) is a heterodimeric molecule made up of two subunits, SPTLC1 and SPTLC2. Twelve index patients from families with presumed genetic sensory neuropathies were screened for SPTLC2 mutations. These families comprised six multigenerational families, including two previously reported families not linked to the SPTLC1 locus on chromosome 9 and one multigenerational family with a complicated hereditary sensory neuropathy syndrome with associated palmar plantar keratosis, ataxia and spastic paraplegia. The remaining families included one consanguineous family with presumed recessive HSN with two affected siblings, one case of congenital sensory neuropathy and four sporadic cases with adult onset sensory neuropathy. No mutations in the SPTLC2 gene were found in any family. These results suggest that SPTLC2 mutations are not a common cause for genetic sensory neuropathies.

A novel chronic childhood sensory predominant neuropathy

Chronic childhood neuropathies are predominantly hereditary in origin. Specific distinct clinical entities have been described, however, occasionally children with an unusual clinical phenotype are encountered in practice. We describe four children (3 males, 1 female) of Lebanese Moslem descent all sharing a common great-great-grandparent pairing with such a novel clinical spectrum. The three males were first cousins, each the product of a different parental consanguineous (i.e., parents second cousins) mating, whereas the female was a third cousin to each of the males whose parents were also second cousins. Each child presented early in life with developmental delay with associated hypotonia and areflexia. All had a sensorineural hearing loss documented and two of the patients were dysmorphic in facial appearance. Nerve conduction studies highlighted a sensory axonal neuropathy and sural nerve biopsy undertaken in two patients confirmed an axonal neuropathy. Detailed genetic and metabolic testing was negative. Followed into later childhood, each child continued to manifest motoric impairment, unsteadiness, areflexia, and cognitive disability. These children appear to provide evidence for a novel autosomal recessive inherited chronic predominantly sensory neuropathy that shares core clinical features with observed variability in associated symptoms.