Yong Yang

Transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel, which can detect various noxious stimuli that cause pain, inflammation, hyperalgesia, and itch. TRPV1 knock-out mice show deficiency in nociception, but the in vivo effects of persistent activation of TRPV1 are not completely understood. Here, we generated TRPV1 knock-in mice with a G564S mutation. In the heterologous expression system, an electrophysiological study showed that the G564S mutation in mouse TRPV1 caused increased basal current and a leftward shift of voltage dependence. Intriguingly, using behavioral analysis, we found that knock-in mice showed a thermosensory defect, impaired inflammatory thermal pain, and capsaicin sensitivity. We also demonstrated an attenuated behavioral response to the pruritic agent histamine in the knock-in mice. Indeed, calcium imaging together with electrophysiology showed that the overactive mutant had decreased capsaicin sensitivity. Western blot analysis revealed that the G564S mutant reduced TRPV1 phosphorylation and cell membrane trafficking. Together, we have generated a mouse model with a gain-of-function mutation in Trpv1 gene and demonstrated that the pain and histamine-dependent itch sensations in these mice are impaired due to a decreased phosphorylation level and reduced membrane localization of TRPV1.

Xeroderma pigmentosum (XP) is a rare genetic disorder which is divided into eight complementation groups: XP‐A to XP‐G and XP‐V. Some XP patients demonstrate severe cutaneous and neurological manifestations, management of which requires timely diagnosis and intervention. We performed clinical evaluation and genetic analysis on 19 patients, the largest cohort of XP to date in China. Twenty‐three mutations from six groups were identified, 16 of which were novel. All patients developed marked freckle‐like pigmentation on sun‐exposed sites while patients with XP‐A, XP‐D, XP‐F and XP‐G showed acute sunburn reactions. Only XP‐A patients displayed progressive neurological degeneration. A relatively larger proportion of XP‐A and XP‐C were found in Chinese XP patients. One XP case and two carriers were prenatally determined. This study extended the mutation spectrum of XP in China and may aid in the diagnosis and treatment of Chinese XP patients.

Inherited epidermodysplasia verruciformis (EV) is a rare skin disorder characterized by susceptibility to specific types of human papilloma virus (HPV) and is strongly associated with skin carcinomas. Inactivating mutations in EVER1/EVER2 account for most cases of EV. However, more phenotypes related to but distinct from EV have been reported with an immunodeficiency state but without EVER1/EVER2 mutation, and the genetic basis for these atypical EV cases is poorly understood. To identify the causative gene responsible for three siblings affected by atypical EV but without EVER1/EVER2 mutation. Whole-exome sequencing followed by Sanger sequencing was performed to identify the gene responsible for the patients with atypical EV enrolled in our study. A homozygous splicing mutation was detected in LCK (c.188-2A>G). This mutation resulted in an exon 3 deletion T lymphocyte-specific protein tyrosine kinase isoform, which further led to frameshift mutation and subsequent mRNA decay. We demonstrate a novel mutation in LCK in a family affected by atypical EV with T-cell defects, HPV infection and virus-induced malignancy, providing new clues in the understanding of host defences against HPV and better genetic counselling of patients with the EV phenotype.

Keratoderma-hypotrichosis-leukonychia totalis syndrome (KHLS) is an extremely rare, autosomal-dominant disorder characterized by severe skin hyperkeratosis, congenital alopecia and leukonychia totalis. The genetic defect underlying KHLS remained undetermined. By performing whole-exome sequencing in a family with KHLS, we identified a heterozygous mutation (c.23G>T [p.Gly8Val]) in GJA1, which cosegregated with the phenotype in the family. In an additional affected individual, we also found the identical de novo mutation which was absent in his unaffected family members. GJA1 encodes a gap junction protein connexin 43 (Cx43) which is ubiquitously expressed in various organs, including the epidermis and hair follicles. In vitro studies on HEK293 cells expressing Cx43^Gly8Val found that the protein formed gap junction plaques between adjacent transfected cells, as observed in the wild-type. Dye-transfer experiments by microinjection of Lucifer yellow displayed functional gap junction of the Cx43^Gly8Val mutant. Using patch clamp and Ca²⁺ imaging methods, we observed that the Cx43^Gly8Val hemichannel had significantly more openings than Cx43^WT, facilitating Ca²⁺ influx at resting potential. Such gain-of-function effect might result in cytoplasmic Ca²⁺ overload, accelerated apoptosis of keratinocytes and subsequent skin hyperkeratosis. Taken together, our results demonstrated that, with probably enhanced hemichannel activities, a mutation in GJA1 is linked to KHLS without extracutaneous involvement.

Inherited erythromelalgia (IEM), an autosomal dominant disorder characterized by severe burning pain in response to mild warmth, has been shown to be caused by gain-of-function mutations of sodium channel Na_v1.7 which is preferentially expressed within dorsal root ganglion (DRG) and sympathetic ganglion neurons. Almost all physiologically characterized cases of IEM have been associated with onset in early childhood. Here, we report the voltage-clamp and current-clamp analysis of a new Na_v1.7 mutation, Q10R, in a patient with clinical onset of erythromelalgia in the second decade. We show that the mutation in this patient hyperpolarizes activation by only −5.3 mV, a smaller shift than seen with early-onset erythromelalgia mutations, but similar to that of I136V, another mutation that is linked to delayed-onset IEM. Using current-clamp, we show that the expression of Q10R induces hyperexcitability in DRG neurons, but produces an increase in excitability that is smaller than the change produced by I848T, an early-onset erythromelalgia mutation. Our analysis suggests a genotype–phenotype relationship at three levels (clinical, cellular and molecular/ion channel), with mutations that produce smaller effects on sodium channel activation being associated with a smaller degree of DRG neuron excitability and later onset of clinical signs.