The remarkable phenotypic variability of the p.Arg269HiS variant in the TRPV4 gene

Recent advances on the structure and the function relationships of the TRPV4 ion channel

The members of the superfamily of Transient Receptor Potential (TRP) ion channels are physiologically important molecules that have been studied for many years and are still being intensively researched. Among the vanilloid TRP subfamily, the TRPV4 ion channel is an interesting protein due to its involvement in several essential physiological processes and in the development of various diseases. As in other proteins, changes in its function that lead to the development of pathological states, have been closely associated with modification of its regulation by different molecules, but also by the appearance of mutations which affect the structure and gating of the channel. In the last few years, some structures for the TRPV4 channel have been solved. Due to the importance of this protein in physiology, here we discuss the recent progress in determining the structure of the TRPV4 channel, which has been achieved in three species of animals (Xenopus tropicalis, Mus musculus, and Homo sapiens), highlighting conserved features as well as key differences among them and emphasizing the binding sites for some ligands that play crucial roles in its regulation.

The implementation and utility of clinical exome sequencing in a South African infant cohort

Genetic disorders are significant contributors to infant hospitalization and mortality globally. The early diagnosis of these conditions in infants remains a considerable challenge. Clinical exome sequencing (CES) has shown to be a successful tool for the early diagnosis of genetic conditions, however, its utility in African infant populations has not been investigated. The impact of the under-representation of African genomic data, the cost of testing, and genomic workforce shortages, need to be investigated and evidence-based implementation strategies accounting for locally available genetics expertise and diagnostic infrastructure need to be developed. We evaluated the diagnostic utility of singleton CES in a cohort of 32 ill, South African infants from two State hospitals in Johannesburg, South Africa. We analysed the data using a series of filtering approaches, including a curated virtual gene panel consisting of genes implicated in neonatal-and early childhood-onset conditions and genes with known founder and common variants in African populations. We reported a diagnostic yield of 22% and identified seven pathogenic variants in the NPHS1, COL2A1, OCRL, SHOC2, TPRV4, MTM1 and STAC3 genes. This study demonstrates the utility value of CES in the South African State healthcare setting, providing a diagnosis to patients who would otherwise not receive one and allowing for directed management. We anticipate an increase in the diagnostic yield of our workflow with further refinement of the study inclusion criteria. This study highlights important considerations for the implementation of genomic medicine in under-resourced settings and in under-represented African populations where variant interpretation remains a challenge.

A TRPV4 mutation caused Charcot-Marie-Tooth disease type 2C with scapuloperoneal muscular atrophy overlap syndrome and scapuloperoneal spinal muscular atrophy in one family: a case report and literature review

BACKGROUND

Charcot-Marie-Tooth disease 2C (CMT2C) and scapuloperoneal spinal muscular atrophy (SPSMA) are different clinical phenotypes of TRPV4 mutation. The mutation of p.R316C has been reported to cause CMT2C and SPSMA separately.

CASE PRESENTATION

Here, we reported a Chinese family harboring the same p.R316C variant, but with an overlap syndrome and different clinical manifestations. A 58-year-old man presented with severe scapula muscle atrophy, resulting in sloping shoulders. He also exhibited distinct muscle atrophy in his four limbs, particularly in the lower limbs. The sural nerve biopsy revealed severe loss of myelinated nerve fibers with scattered regenerating clusters and pseudo-onion bulbs. Nerve conduction study showed axon damage in both motor and sensory nerves. Sensory nerve action potentials could not be evoked in bilateral sural or superficial peroneal nerves. He was diagnosed with Charcot-Marie-Tooth disease type 2C and scapuloperoneal muscular atrophy overlap syndrome, whereas his 27-year-old son was born with clubfoot and clinodactyly. Electromyogram examination indicated chronic neurogenic changes and anterior horn cells involvement. Although there was no obvious weakness or sensory symptoms, early SPSMA could be considered for him.

CONCLUSIONS

A literature review of the clinical characteristics in CMT2C and SPSMA patients with TRPV4 mutation suggested that our case was distinct due to the overlap syndrome and phenotype variation. Altogether, this case broadened the phenotype spectrum and provided the nerve biopsy pathological details of TRPV4-related neuropathies.

Exploring and expanding the phenotype and genotype diversity in seven Chinese families with spondylo-epi-metaphyseal dysplasia

Spondylo-epi-metaphyseal dysplasia (SEMD) is a heterogeneous group of disorders with different modes of inheritance and is characterized by disproportionate or proportionate short stature. To date, more than 30 disease-causing genes have been identified, and different types of SEMD exhibit greatly overlapping clinical features, which usually complicate the diagnosis. This study was performed to expand the clinical and molecular spectrum of SEMD among Chinese subjects and to explore their potential phenotype–genotype relations. We enrolled seven families including 11 affected patients with SEMD, and their clinical, radiographic, and genetic data were carefully analyzed. All the seven probands showed different degrees of short stature, and each of them exhibited additional specific skeletal manifestations; four probands had extraosseous manifestations. X-rays of the seven probands showed common features of SEMD, including vertebral deformities, irregular shape of the epiphysis, and disorganization of the metaphysis. Seven variants were identified in TRPV4 (c.694C> T, p.Arg232Cys), COL2A1 (c.654 + 1G > C; c.3266_3268del, p.Gly1089del), CCN6 (c.396 T> G, p.Cys132Trp; c.721 T>C, p.Cys241Arg), SBDS (c.258 + 2T> C), and ACAN (c.1508C> A, p.Thr503Lys) genes, and two of them were novel. Two families with TRPV4 variants showed considerable intrafamily and interfamily heterogeneities. In addition, we reported one case of SEMD with a severe phenotype caused by ACAN gene mutation. Our study expands the phenotype and genetic spectrum of SEMD and provides evidence for the phenotype–genotype relations, aiding future molecular and clinical diagnosis as well as procreative management of SEMD.

[CASE REPORT] Homozygous N-terminal missense variant in PLEKHG5 associated with intermediate CMT: a case report

Mutations in PLEKHG5, a pleckstrin homology domain containing member of the GEF family, are associated with distal spinal muscular atrophy and intermediate Charcot-Marie-Tooth disease. Here, we describe an isolated case with distal intermediate neuropathy with scapular winging. By whole exome sequencing, we identified the homozygous PLEKHG5 Arg97Gln missense mutation, located in the N-terminal region of the protein. This mutation resides between a zinc-finger motif and a RBD domain, involved in binding rnd3, a RhoA effector protein. We conclude that based on the characteristic phenotype presented by the patient and the supportive genetic findings, the PLEKHG5 mutation is the causative variant.

Natural history of TRPV4-Related disorders: From skeletal dysplasia to neuromuscular phenotype

TRPV4-related disorders constitute a broad spectrum of clinical phenotypes including several genetic skeletal and neuromuscular disorders, in which clinical variability and somewhat overlapping features are present. These disorders have previously been considered to be clinically distinct phenotypes before their molecular basis was discovered. However, with the identification of TRPV4 variants in the etiology, they are referred as TRPV4-related disorders (TRPV4-pathies), and are now mainly grouped into skeletal dysplasias and neuromuscular disorders. The skeletal dysplasia group includes metatropic dysplasia, parastremmatic dysplasia, spondyloepiphyseal dysplasia Maroteaux type, spondylometaphyseal dysplasia Kozlowski type, autosomal dominant brachyolmia, and familial digital arthropathy-brachydactyly, whereas the neuromuscular group includes congenital distal spinal muscular atrophy (SMA), scapuloperoneal SMA and Charcot-Marie-Tooth neuropathy type 2C with common manifestations of peripheral neuropathy, joint contractures, and respiratory system involvement. Apart from familial digital arthropathy-brachydactyly, skeletal dysplasia associated with TRPV4 pathogenic variants share some clinical features such as short stature with short trunk, spinal and pelvic changes with varying degrees of long bone involvement. Of note, there is considerable phenotypic overlap within and between both groups. Herein, we report on the clinical and molecular spectrum of 11 patients from six different families diagnosed with TRPV4-related disorders. This study yet represents the largest cohort of patients with TRPV4 variants from a single center in Turkey.