We report a case of hereditary sensory and autonomic neuropathy presenting with childhood-onset symmetric distally predominant limb hypoesthesia to tactile, thermal, and painful stimuli. Exome sequencing identified a homozygous pathogenic variant in the with-no-lysine (K) kinase 1 (WNK1), lysine deficient protein kinase 1 gene. The clinical, electrophysiological, and genetic findings confirmed a diagnosis of hereditary sensory and autonomic neuropathy type 2A (HSAN 2A). This case highlights the importance of genetic confirmation in the evaluation of early-onset neuropathies, especially when the most common causes have been ruled out. Significantly, our observations underscore the potential role of skin biopsy in identifying autonomic abnormalities in HSAN 2, possibly contributing to a better understanding of these rare neuropathies. We also reviewed the reported cases of this disease in the literature to highlight its phenotypic variability.

Hereditary sensory and autonomic neuropathy type 2 (HSAN2) is a group of extremely rare autosomal recessive neurological disorders characterized by predominant sensory dysfunction and attendant severe complications, such as limb destruction. Our study reports a Chinese patient who met the diagnostic criteria for HSAN2 and harbored a homozygous mutation in the WNK1 gene (NM_213655.4: c.2689 G > T; p. Glu897*), Which led to nonsense-mediated mRNA decay of the transcript. Sanger sequencing revealed that the mutation segregates with disease status in the pedigree. These results expanded the spectrum of mutations in the WNK1 gene by identifying a novel mutation in a Chinese patient, providing a valuable reference for clinical diagnosis and treatment.

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.

KIF1A (kinesin family member 1A)-related disorders encompass a variety of diseases. KIF1A variants are responsible for autosomal recessive and dominant spastic paraplegia 30 (SPG, OMIM610357), autosomal recessive hereditary sensory and autonomic neuropathy type 2 (HSN2C, OMIM614213), and autosomal dominant neurodegeneration and spasticity with or without cerebellar atrophy or cortical visual impairment (NESCAV syndrome), formerly named mental retardation type 9 (MRD9) (OMIM614255). KIF1A variants have also been occasionally linked with progressive encephalopathy with brain atrophy, progressive neurodegeneration, PEHO-like syndrome (progressive encephalopathy with edema, hypsarrhythmia, optic atrophy), and Rett-like syndrome. The first Polish patients with confirmed heterozygous pathogenic and potentially pathogenic KIF1A variants were analyzed. All the patients were of Caucasian origin. Five patients were females, and four were males (female-to-male ratio = 1.25). The age of onset of the disease ranged from 6 weeks to 2 years. Exome sequencing identified three novel variants. Variant c.442G>A was described in the ClinVar database as likely pathogenic. The other two novel variants, c.609G>C; p.(Arg203Ser) and c.218T>G, p.(Val73Gly), were not recorded in ClinVar. The authors underlined the difficulties in classifying particular syndromes due to non-specific and overlapping signs and symptoms, sometimes observed only temporarily.

Amyotrophic lateral sclerosis (ALS) is a devastating progressive neurodegenerative disease that affects neurons in the central nervous system and the spinal cord. As in many other neurodegenerative disorders, the genetic risk factors and pathogenesis of ALS involve dysregulation of cytoskeleton and neuronal transport. Notably, sensory and motor neuron diseases such as hereditary sensory and autonomic neuropathy type 2 (HSAN2) and spastic paraplegia 30 (SPG30) share several causative genes with ALS, as well as having common clinical phenotypes. KIF1A encodes a kinesin 3 motor that transports presynaptic vesicle precursors (SVPs) and dense core vesicles and has been reported as a causative gene for HSAN2 and SPG30. Here, we analyzed whole-exome sequencing data from 941 patients with ALS to investigate the genetic association of KIF1A with ALS. We identified rare damage variants (RDVs) in the KIF1A gene associated with ALS and delineated the clinical characteristics of ALS patients with KIF1A RDVs. Clinically, these patients tended to exhibit sensory disturbance. Interestingly, the majority of these variants are located at the C-terminal cargo-binding region of the KIF1A protein. Functional examination revealed that the ALS-associated KIF1A variants located in the C-terminal region preferentially enhanced the binding of SVPs containing RAB3A, VAMP2, and synaptophysin. Expression of several disease-related KIF1A mutants in cultured mouse cortical neurons led to enhanced colocalization of RAB3A or VAMP2 with the KIF1A motor. Our study highlighted the importance of KIF1A motor-mediated transport in the pathogenesis of ALS, indicating KIF1A as an important player in the oligogenic scenario of ALS. Hereditary sensory and autonomic neuropathy type II (HSAN2) is characterized by progressively reduced sensation to pain, temperature, and touch. Onset can be at birth and is often before puberty. The sensory deficit is predominantly distal with the lower limbs more severely affected than the upper limbs. Over time sensory function becomes severely reduced. Unnoticed injuries and neuropathic skin promote ulcerations and infections that result in spontaneous amputation of digits or the need for surgical amputation. Osteomyelitis is common. Painless fractures can complicate the disease. Autonomic disturbances are variable and can include hyperhidrosis, tonic pupils, and urinary incontinence in those with more advanced disease. The diagnosis of HSAN2 is established in a proband with suggestive clinical and electrophysiologic findings and biallelic pathogenic variants in one of four genes: KIF1A, RETREG1 (FAM134B), SCN9A, or WNK1. Treatment of manifestations: Treatment is symptomatic and often involves a team including neurologists, orthopedic surgeons, and physiotherapists. Training in the care of the sensory-impaired limb, often in a diabetic foot care clinic, is important and includes self-examination – especially of the feet – for any signs of trauma. To prevent osteomyelitis, and hence the need for amputation, wounds require cleaning and protection along with antiseptic treatment. To prevent callous formation, the skin of neuropathic limbs requires hydration and lipid-based unguents. Appropriate shoes and socks are recommended. Surveillance: The feet should be inspected daily for injuries or sources of wear. Annual follow up in centers with comprehensive care of diabetics and/or persons with Charcot-Marie-Tooth neuropathy is recommended. Agents/circumstances to avoid: Ill-fitting shoes or other sources of trauma to the feet or hands (e.g., use protective gloves when handling hot items when cooking.) HSAN2 is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an HSAN2-causing pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once the HSAN2-causing pathogenic variants in the family are known, carrier testing of at-risk relatives, prenatal testing for pregnancies at increased risk, and preimplantation genetic testing are possible.