Hereditary sensory and autonomic neuropathy type IC accompanied by upper motor neuron abnormalities and type II juxtafoveal retinal telangiectasias

Hereditary sensory and autonomic neuropathy type I (HSAN‐1) is an autosomal dominant sensory neuropathy occurring secondary to mutations in the SPTLC1 and SPTLC2 genes. We present two generations of a single family with Ser384Phe mutation in the SPTLC2 gene located on chromosome 14q24 characterized by a typical HSAN‐1c presentation, with additional findings upper motor neuron signs, early demyelinating features on nerve conduction studies, and type II juxtafoveal retinal telangiectasias also known as macular telangiectasias (MacTel II). Although HSAN1 is characterized as an axonal neuropathy, demyelinating features were identified in two subjects on serial nerve conduction studies comprising motor conduction block, temporal dispersion, and prolongation of F‐waves. MacTell II is a rare syndrome characterized by bilateral macular depigmentation and Müller cell loss. It has a presumed genetic basis, and these cases suggest that the accumulation of toxic sphingoplipids may lead to Müller cell degeneration, subsequent neuronal loss, depigmentation, and progressive central macular thinning.     

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.     

Frequency of mutations in the genes associated with hereditary sensory and autonomic neuropathy in a UK cohort

The hereditary sensory and autonomic neuropathies (HSAN, also known as the hereditary sensory neuropathies) are a clinically and genetically heterogeneous group of disorders, characterised by a progressive sensory neuropathy often complicated by ulcers and amputations, with variable motor and autonomic involvement. To date, mutations in twelve genes have been identified as causing HSAN. To study the frequency of mutations in these genes and the associated phenotypes, we screened 140 index patients in our inherited neuropathy cohort with a clinical diagnosis of HSAN for mutations in the coding regions of SPTLC1, RAB7, WNK1/HSN2, FAM134B, NTRK1 (TRKA) and NGFB. We identified 25 index patients with mutations in six genes associated with HSAN (SPTLC1, RAB7, WNK1/HSN2, FAM134B, NTRK1 and NGFB); 20 of which appear to be pathogenic giving an overall mutation frequency of 14.3%. Mutations in the known genes for HSAN are rare suggesting that further HSAN genes are yet to be identified. The p.Cys133Trp mutation in SPTLC1 is the most common cause of HSAN in the UK population and should be screened first in all patients with sporadic or autosomal dominant HSAN.     

SPTLC1 and RAB7 mutation analysis in dominantly inherited and idiopathic sensory neuropathies

BACKGROUND: The variable clinical features of hereditary sensory and autonomic neuropathy (HSAN I) suggest heterogeneity. Some cases of idiopathic sensory neuropathy could be caused by missense mutations of SPTLC1 and RAB7 and not be recognised as familial. OBJECTIVE: To screen persons with dominantly inherited HSAN I and others with idiopathic sensory neuropathies for known mutations of SPTLC1 and RAB7. PATIENTS: DNA was examined from well characterised individuals of 25 kindreds with adult onset HSAN I for mutations of SPTLC1 and RAB7; 92 patients with idiopathic sensory neuropathy were also screened for known mutations of these genes. RESULTS: Of the 25 kindreds, only one had a mutation (SPTLC1 399T-->G). This kindred, and 10 without identified mutations, had prominent mutilating foot injuries with peroneal weakness. Of the remainder, 12 had foot insensitivity with injuries but no weakness, one had restless legs and burning feet, and one had dementia with hearing loss. No mutation of RAB7 was found in any of these. No known mutations of SPTLC1 or RAB7 were found in cases of idiopathic sensory neuropathy. CONCLUSIONS: Adult onset HSAN I is clinically and genetically heterogeneous and further work is required to identify additional genetic causes. Known SPTLC1or RAB7 mutations were not found in idiopathic sensory neuropathy.     

Late‐onset hereditary sensory and autonomic neuropathy expands the phenotypic spectrum of MFN2‐related diseases

Mutations in the Mitofusin 2 (MFN2) gene have been identified in patients with autosomal dominant axonal motor and sensory neuropathy or Charcot–Marie‐Tooth 2A (CMT2A). Here we describe clinical and pathological changes in an adult patient with sporadic hereditary sensory and autonomic neuropathy (HSAN) due to an MFN2 mutation. The patient was a 53‐year‐old man who had sensory involvement and anhidrosis in all limbs without motor features. The electrophysiological assessment documented severe axonal sensory neuropathy. The sural nerve biopsy confirmed the electrophysiological findings, revealing severe loss of myelinated and unmyelinated fibers with regeneration clusters. Genetic analysis revealed the previously identified mutation c.776 G > A in MFN2. Our report expands the phenotypic spectrum of MFN2‐related diseases. Sequencing of MFN2 should be considered in all patients presenting with late‐onset HSAN.     

A systematic comparison of all mutations in hereditary sensory neuropathy type I (HSAN I) reveals that the G387A mutation is not disease associated

Hereditary sensory neuropathy type 1 (HSAN I) is an autosomal dominant inherited neurodegenerative disorder of the peripheral nervous system associated with mutations in the SPTLC1 subunit of the serine palmitoyltransferase (SPT). Four missense mutations (C133W, C133Y, V144D and G387A) in SPTLC1 were reported to cause HSAN I. SPT catalyses the condensation of Serine and Palmitoyl-CoA, which is the first and rate-limiting step in the de novo synthesis of ceramides. Earlier studies showed that C133W and C133Y mutants have a reduced activity, whereas the impact of the V144D and G387A mutations on the human enzyme was not tested yet. In this paper, we show that none of the HSAN I mutations interferes with SPT complex formation. We demonstrate that also V144D has a reduced SPT activity, however to a lower extent than C133W and C133Y. In contrast, the G387A mutation showed no influence on SPT activity. Furthermore, the growth phenotype of LY-B cells—a SPTLC1 deficient CHO cell line—could be reversed by expressing either the wild-type SPTLC1 or the G387A mutant, but not the C133W mutant. This indicates that the G387A mutation is most likely not directly associated with HSAN I. These findings were genetically confirmed by the identification of a nuclear HSAN family which showed segregation of the G387A variant as a non-synonymous SNP.     

Hereditary sensory autonomic neuropathy type II: Report of two novel mutations in the FAM134B gene

Hereditary sensory autonomic neuropathy (HSAN) type II is a rare, autosomal recessive, and early onset sensory neuropathy, characterized by severe and progressive sensation impairment, leading to ulcero‐mutilating complications. FAM134B gene, also known as RETREG1 gene, mutations have been reported to be associated to HSAN‐IIB. We report four patients from two unrelated families who developed during childhood a sensory axonal neuropathy with variable severity and pronounced nociception impairment. Complications such as recurrent ulcerations, osteomyelitis, and osteonecrosis leading to distal amputation were noticed. Dysautonomia was mild or even absent in our group of patients. Additionally, either clinical or neurophysiological motor impairment was not uncommon. Presence of upper motor neuron signs was also a distinctive feature in two related patients. After extensive workup, two novel homozygous mutations in the FAM134B gene were identified. This report expands the clinical and genetic spectrum of HSAN type II and emphasizes the phenotype variability even within the same family.     

Novel mutation in the replication focus targeting sequence domain of DNMT1 causes hereditary sensory and autonomic neuropathy IE

DNMT1, encoding DNA methyltransferase 1 (Dnmt1), is a critical enzyme which is mainly responsible for conversion of unmethylated DNA into hemimethylated DNA. To date, two phenotypes produced by DNMT1 mutations have been reported, including hereditary sensory and autonomic neuropathy (HSAN) type IE with mutations in exon 20, and autosomal dominant cerebellar ataxia, deafness, and narcolepsy caused by mutations in exon 21. We report a sporadic case in a Japanese patient with loss of pain and vibration sense, chronic osteomyelitis, autonomic system dysfunctions, hearing loss, and mild dementia, but without definite cerebellar ataxia. Electrophysiological studies revealed absent sensory nerve action potential with nearly normal motor nerve conduction studies. Brain magnetic resonance imaging revealed mild diffuse cerebral and cerebellar atrophy. Using a next‐generation sequencing system, 16 candidate genes were analyzed and a novel missense mutation, c.1706A>G (p.His569Arg), was identified in exon 21 of DNMT1. Our findings suggest that mutation in exon 21 of DNMT1 may also produce a HSAN phenotype. Because all reported mutations of DNMT1 are concentrated in exons 20 and 21, which encode the replication focus targeting sequence (RFTS) domain of Dnmt1, the RFTS domain could be a mutation hot spot.     

A novel DNMT1 mutation associated with early onset hereditary sensory and autonomic neuropathy,cataplexy, cerebellar atrophy,scleroderma, endocrinopathy,and common variable immune deficiency

DNA methyltransferase 1 (DNMT1) is an enzyme which has a role in methylation of DNA, gene regulation, and chromatin stability. Missense mutations in the DNMT1 gene have been previously associated with two neurological syndromes: hereditary sensory and autonomic neuropathy type 1 with dementia and deafness (HSAN1E) and autosomal dominant cerebellar ataxia, deafness, and narcolepsy (ADCA‐DN). We report a case showing overlap of both of these syndromes plus associated clinical features of common variable immune deficiency, scleroderma, and endocrinopathy that could also be mutation associated. Our patient was found to be heterozygous for a previously unreported frameshift mutation, c.1635_1637delCAA p.(Asn545del) in the DNMT1 gene exon 20. This case displays both the first frameshift mutation described in the literature which is associated with a phenotype with a high degree of overlap between HSAN1E and ADCA‐DN and early age of onset (c. 8 years). Our case is also of interest as the patient displays a number of new non‐neurological features, which could also be DNMT1 mutation related.     

Inherited autonomic neuropathies

Inherited autonomic neuropathies are a rare group of disorders associated with sensory dysfunction. As a group they are termed the "hereditary sensory and autonomic neuropathies" (HSAN). Classification of the various autonomic and sensory disorders is ongoing. In addition to the numerical classification of four distinct forms proposed by Dyck and Ohta (1975), additional entities have been described. The best known and most intensively studied of the HSANs are familial dysautonomia (Riley-Day syndrome or HSAN type III) and congenital insensitivity to pain with anhidrosis (HSAN type IV). Diagnosis of the HSANs depends primarily on clinical examinations and specific sensory and autonomic assessments. Pathologic examinations are helpful in confirming the diagnosis and in differentiating between the different disorders. In recent years identification of specific genetic mutations for some disorders has aided diagnosis. Replacement or definitive therapies are not available for any of the disorders so that treatment remains supportive and directed toward specific symptoms.     

Haploinsufficiency of the nerve growth factor beta gene in a 1p13 deleted female child with an insensitivity to pain

Pain insensitivity is mediated at the genetic level by the disruption of specific genes associated with neuronal development. Mammalian in vivo and in vitro studies have shown the nerve growth factor (NGF) gene to play an integral role in nerve maintenance and function. Pain insensitivity in humans can be attributed to hereditary sensory and autonomic neuropathies (HSAN) of which there are five classes (HSAN I – HSAN V). The human nerve growth factor beta gene (NGFB) located on chromosome 1p13.2 has been found to cause HSAN V within individuals homozygous for a point mutation in NGFB. Although heterozygotes can display a milder phenotype, this has only been observed in adults. We report a karyotypically normal 5-year-old female with developmental delay, mild facial dysmorphism, and unsteady gait. Pain and thermal insensitivity were noted as were recurrent mouth ulcers, facial flushing, recurrent episodes of increased body temperature and unexplained sweating, indicative of a sensory neuropathy with mild autonomic involvement. Array comparative genomic hybridization (aCGH) analysis revealed a de-novo deletion within chromosome 1p13 of the child involving the NGFB gene. Sequence analysis of the homologous NGFB gene identified no mutation, implying that sensory neuropathy was caused by haploinsufficiency of the NGFB gene.     

Beyond neuropathy in hereditary sensory and autonomic neuropathy type V: cognitive evaluation

Background and purpose:  Hereditary sensory and autonomic neuropathy (HSAN) type V is a very rare disorder. It is characterized by the absence of thermal and mechanical pain perception caused by decreased number of small diameter neurons in peripheral nerves. Recent genetic studies have pointed out the aetiological role of nerve growth factor beta, which is also involved in the development of the autonomic nervous system and cholinergic pathways in the brain. HSAN type V is usually reported not to cause mental retardation or cognitive decline. However, a structured assessment of the cognitive profile of these patients has never been made.
Methods and results:  We performed a throughout evaluation of four HSAN type V patients and compared their performance with 37 normal individuals. Our patients showed no cognitive deficits, not even mild ones.
Discussion and Conclusions:  Although newer mutations on this and related disorders are continuously described, their clinical characterization has been restricted to the peripheral aspects of these conditions. A broader characterization of this rare disorder may contribute to better understand the mechanisms of the nociceptive and cognitive aspects of pain.     

Homozygous splice‐site mutation c.78 + 5G>A in PMP22 causes congenital hypomyelinating neuropathy

Congenital hypomyelinating neuropathy (CHN) presents in the neonatal period and results in delayed development of sensory and motor functions due to several gene mutations including in EGR2, MPZ, CNTNAP1, and PMP22. The phenotype of homozygous splice‐site mutation in the PMP22 gene has not been described in humans or animal models. Here we describe a family carrying a pathogenic splice‐site c.78 + 5G>A mutation in the PMP22 gene. We evaluated the clinical, electrophysiological, histological, and genetic features of the family. The proband with homozygous mutation presented with CHN, while his consanguineous parents with heterozygous mutation were asymptomatic. The proband was a 7‐year‐old boy. He had motor retardation after birth and had remained unable to walk independently at the time of the study. The compound muscle action potentials and sensory nerve action potentials were not recordable in the boy. The motor and sensory nerve conduction velocities of the parents were slightly to moderately decreased, although they had no symptoms of peripheral neuropathy. The sural nerve biopsy of the boy revealed hypomyelinating neuropathy with absence of large myelinated fibers, no myelin breakdown products, and numerous basal lamina onion bulb formations. To our knowledge, this is the first report of a homozygous splice‐site mutation in the PMP22 gene in humans. Our study expands the phenotype and genotype of PMP22‐related neuropathy.     

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.     

A novel mutation of the ε‐sarcoglycan gene in a Chinese family with myoclonus‐dystonia syndrome

In a Chinese myoclonus‐dystonia syndrome (MDS) family presented with a phenotype including a typical MDS, cervical dystonia, and writer's cramp, genetic analyses revealed a novel 662 + 1insG heterozygous mutation in exon 5 in the ε‐sarcoglycan (SGCE) gene, leading to a frameshift with a down stream stop codon. Low SGCE mRNA levels were detected in the mutation carriers by real‐time PCR, suggesting that the nonsense mutation might interference with the stability of SGCE mRNA. This is the first report on Chinese with a SGCE mutation leading to MDS. Our data support the fact that same mutation of SGCE gene can lead to a varied phenotype, even in the same family. © 2008 Movement Disorder Society     

Sensitive quantitative detection of somatic mosaic mutation in “double cortex” syndrome

Aims. Somatic mutation of the lissencephaly‐1 gene is a cause of subcortical band heterotopia (“double cortex”). The severity of the phenotype depends on the level of mutation in brain tissue. Detecting and quantifying low‐level somatic mosaic mutations is challenging. Here, we utilized droplet digital PCR, a sensitive method to detect low‐level mutation. Methods. Droplet digital PCR was used in concert with classic genotyping techniques (SNaPshot assays and pyrosequencing) to detect and characterize the tissue mosaicism of a somatic mutation (LIS1 c.190A>T; p.K64X) in a patient with posterior bilateral SBH and refractory epilepsy. Results. The high sensitivity of droplet digital PCR and the ability to target individual DNA molecules allowed us to detect the mutation at low level in the brain, despite the low quality of the DNA sample derived from formalin‐fixed paraffin‐embedded tissue. This low mutation frequency in the brain was consistent with the relatively subtle malformation resolved by magnetic resonance imaging. The presence of the mutation in other tissues from the patient permitted us to predict the timing of mutagenesis. Conclusion. This sensitive methodology will have utility for a variety of other brain malformation syndromes associated with epilepsy for which historical pathological specimens are available and specific somatic mosaic mutations are predicted.     

Novel missense, insertion and deletion mutations in the neurotrophic tyrosine kinase receptor type 1 gene (NTRK1) associated with congenital insensitivity to pain with anhidrosis

Hereditary sensory and autonomic neuropathy type IV (HSAN IV) or congenital insensitivity to pain with anhidrosis (CIPA) is an autosomal-recessive disorder affecting the neurotrophin signal transduction pathway. HSAN IV is characterized by absence of reaction to noxious stimuli, recurrent episodes of fever, anhidrosis, self mutilating behaviour and frequent mental retardation. Mutations in the neurotrophic tyrosine kinase receptor type 1 (NTRK1) are associated with this disorder. We investigated NTRK1 mutations in five HSAN IV patients and one less typical patient with hypohidrosis, insensitivity to pain as well as motor- and sensory deficits in the peripheral nervous system. For the HSAN IV patients we identified a homozygous missense mutation (p.I572S), a homozygous deletion of 1985bp (g.7335164-7336545del), a homozygous insertion c.722_723insC in exon 7 and two compound heterozygous mutations (p.Q558X+p.L717R). The less typical patient as well as one HSAN IV patient revealed no NTRK1 mutation.     

Novel frameshift and splice site mutations in the neurotrophic tyrosine kinase receptor type 1 gene (NTRK1) associated with hereditary sensory neuropathy type IV

Congenital insensitivity to pain with anhidrosis or hereditary sensory and autonomic neuropathy type IV (HSAN IV) is the first human genetic disorder implicated in the neurotrophin signal transduction pathway. HSAN IV is characterized by absence of reaction to noxious stimuli, recurrent episodes of fever, anhidrosis, self-mutilating behavior and often mental retardation. Mutations in the neurotrophic tyrosine kinase, receptor, type 1 (NTRK1) are associated with this disorder. Here we report four homozygous mutations, two frameshift (p.Gln626fsX6 and p.Gly181fsX58), one missense (p.Arg761Trp) and one splice site (c.359+5G>T) mutation in four HSAN IV patients. The splice site mutation caused skipping of exons 2 and 3 in patient's mRNA resulting in an in-frame deletion of the second leucine-rich motif. NTRK1 mutations are only rarely reported in the European population. This report extends the spectrum of NTRK1 mutations observed in patients diagnosed with HSAN IV.