Expanding the Genotypic Spectrum of Congenital Sensory and Autonomic Neuropathies Using Whole-Exome Sequencing

Novel TECPR2 variant in two cases of hereditary sensory and autonomic neuropathy type 9: insights from genetic characterization and comprehensive literature review

BACKGROUND

Hereditary sensory and autonomic neuropathy type 9 (HSAN9) is a rare genetic disorder caused by genetic alterations in the TECPR2 locus and is characterized by developmental and intellectual disability, respiratory dysfunction, gastroesophageal reflux disease (GERD), and sensory and autonomic dysfunction, which are shared among the HSAN family.

METHODS

Whole-exome sequencing (WES) was performed on samples from both probands, and the relevant genetic variants were confirmed in their families using Sanger sequencing. Additionally, a comprehensive literature review was conducted on previously reported cases of HSAN9, and the clinical and genetic data were assessed to provide insight into the genetic and clinical characteristics of the disease.

RESULTS

We identified two new cases of HSAN9 with a shared novel variant of TECPR2 (NM_014844.5), c.1568del: p.Ser523PhefsTer12, classified as pathogenic according to ACMG guidelines. The probands showed characteristics of GERD, respiratory dysfunction, gait abnormalities, and developmental and speech delay, and both cases were deceased as a result of severe respiratory infection. The results of the literature review included 34 cases from 9 studies, revealing a wide range of genetic and clinical characteristics.

CONCLUSIONS

Our study identified two new cases of HSAN9 with a novel variant in TECPR2, confirmed by WES. The clinical characteristics of the patients as well as the conduction of a comprehensive literature review are crucial in the early diagnosis and management of the disease and establishment of genotype-phenotype correlations.

Genetic landscape of congenital insensitivity to pain and hereditary sensory and autonomic neuropathies

Congenital insensitivity to pain (CIP) and hereditary sensory and autonomic neuropathies (HSAN) are clinically and genetically heterogeneous disorders exclusively or predominantly affecting the sensory and autonomic neurons. Due to the rarity of the diseases and findings based mainly on single case reports or small case series, knowledge about these disorders is limited. Here, we describe the molecular workup of a large international cohort of CIP/HSAN patients including patients from normally under-represented countries. We identify 80 previously unreported pathogenic or likely pathogenic variants in a total of 73 families in the >20 known CIP/HSAN-associated genes. The data expand the spectrum of disease-relevant alterations in CIP/HSAN, including novel variants in previously rarely recognized entities such as ATL3-, FLVCR1- and NGF-associated neuropathies and previously under-recognized mutation types such as larger deletions. In silico predictions, heterologous expression studies, segregation analyses and metabolic tests helped to overcome limitations of current variant classification schemes that often fail to categorize a variant as disease-related or benign. The study sheds light on the genetic causes and disease-relevant changes within individual genes in CIP/HSAN. This is becoming increasingly important with emerging clinical trials investigating subtype or gene-specific treatment strategies.

Living without pain. Case series of patients with hereditary sensory and autonomic neuropathies in a Canadian tertiary care centre

Background

Hereditary sensory and autonomic neuropathies (HSANs) are a group of heterogeneous genetic disorders presenting predominantly with sensory and autonomic dysfunction. They are a diverse group of diseases of the peripheral nervous system characterized by profound distal sensory loss and various autonomic and motor disturbances.

Objectives

The primary objective of this study was to describe the clinical presentation of children with HSAN to paediatricians. We present clinical features and genetic etiology of patients with HSAN followed in a Canadian tertiary paediatric centre, including suggestions for their monitoring, management, and long-term follow-up.

Methods

A retrospective chart review of all patients with HSAN followed from the years 2000 through 2021 was performed. Collected data consisted of patients' demographics, clinical characteristics, imaging, and management.

Results

Eight patients were included. The average age at diagnosis was 3.19 ± 2.83 years. Insensitivity to pain (100%), dysautonomia (100%), global development delay (87.5%), emesis (62.5%), and self-injury (62.5%) were the most prevalent manifestations of HSAN. The most common co-morbidities were gastroesophageal reflux disease (50%), obstructive sleep apnea (37.5%), attention-deficit hyperactivity disorder (37.5%), and iron deficiency (37.5%). Management was multi-disciplinary, involving neurologists, orthopeds, developmental paediatricians, sleep specialists, and psychiatrists.

Conclusion

HSANs are a diverse group of diseases, characterized by profound distal sensory loss, acral mutilations, and variable autonomic disturbances. It is important to recognize the diagnosis in the paediatrician's office in order to set up surveillance and prevent complications.

Genetic pain loss disorders

Genetic pain loss includes congenital insensitivity to pain (CIP), hereditary sensory neuropathies and, if autonomic nerves are involved, hereditary sensory and autonomic neuropathy (HSAN). This heterogeneous group of disorders highlights the essential role of nociception in protecting against tissue damage. Patients with genetic pain loss have recurrent injuries, burns and poorly healing wounds as disease hallmarks. CIP and HSAN are caused by pathogenic genetic variants in >20 genes that lead to developmental defects, neurodegeneration or altered neuronal excitability of peripheral damage-sensing neurons. These genetic variants lead to hyperactivity of sodium channels, disturbed haem metabolism, altered clathrin-mediated transport and impaired gene regulatory mechanisms affecting epigenetic marks, long non-coding RNAs and repetitive elements. Therapies for pain loss disorders are mainly symptomatic but the first targeted therapies are being tested. Conversely, chronic pain remains one of the greatest unresolved medical challenges, and the genes and mechanisms associated with pain loss offer new targets for analgesics. Given the progress that has been made, the coming years are promising both in terms of targeted treatments for pain loss disorders and the development of innovative pain medicines based on knowledge of these genetic diseases.

PRDM12 in Health and Diseases

PRDM12 is a member of the PRDI-BF1 (positive regulatory domain I-binding factor 1) homologous domain (PRDM)-containing protein family, a subfamily of Kruppel-like zinc finger proteins, controlling key processes in the development of cancer. PRDM12 is expressed in a spatio-temporal manner in neuronal systems where it exerts multiple functions. PRDM12 is essential for the neurogenesis initiation and activation of a cascade of downstream pro-neuronal transcription factors in the nociceptive lineage. PRDM12 inactivation, indeed, results in a complete absence of the nociceptive lineage, which is essential for pain perception. Additionally, PRDM12 contributes to the early establishment of anorexigenic neuron identity and the maintenance of high expression levels of pro-opiomelanocortin, which impacts on the program bodyweight homeostasis. PRDMs are commonly involved in cancer, where they act as oncogenes/tumor suppressors in a “Yin and Yang” manner. PRDM12 is not usually expressed in adult normal tissues but its expression is re-activated in several cancer types. However, little information is currently available on PRDM12 expression in cancers and its mechanism of action has not been thoroughly described. In this review, we summarize the recent findings regarding PRDM12 by focusing on four main biological processes: neurogenesis, pain perception, oncogenesis and cell metabolism. Moreover, we wish to highlight the importance of future studies focusing on the PRDM12 signaling pathway(s) and its role in cancer onset and progression.