Rosacea Core Domain Set for Clinical Trials and Practice: A Consensus Statement

Importance

Inconsistent reporting of outcomes in clinical trials of rosacea is impeding and likely preventing accurate data pooling and meta-analyses. There is a need for standardization of outcomes assessed during intervention trials of rosacea.

Objective

To develop a rosacea core outcome set (COS) based on key domains that are globally relevant and applicable to all demographic groups to be used as a minimum list of outcomes for reporting by rosacea clinical trials, and when appropriate, in clinical practice.

Evidence Review

A systematic literature review of rosacea clinical trials was conducted. Discrete outcomes were extracted and augmented through discussions and focus groups with key stakeholders. The initial list of 192 outcomes was refined to identify 50 unique outcomes that were rated through the Delphi process Round 1 by 88 panelists (63 physicians from 17 countries and 25 patients with rosacea in the US) on 9-point Likert scale. Based on feedback, an additional 11 outcomes were added in Round 2. Outcomes deemed to be critical for inclusion (rated 7-9 by ≥70% of both groups) were discussed in consensus meetings. The outcomes deemed to be most important for inclusion by at least 85% of the participants were incorporated into the final core domain set.

Findings

The Delphi process and consensus-building meetings identified a final core set of 8 domains for rosacea clinical trials: ocular signs and symptoms; skin signs of disease; skin symptoms; overall severity; patient satisfaction; quality of life; degree of improvement; and presence and severity of treatment-related adverse events. Recommendations were also made for application in the clinical setting.

Conclusions and Relevance

This core domain set for rosacea research is now available; its adoption by researchers may improve the usefulness of future trials of rosacea therapies by enabling meta-analyses and other comparisons across studies. This core domain set may also be useful in clinical practice.

Early-life inflammation primes a T helper 2 cell-fibroblast niche in skin

Inflammation early in life can prime the local immune milieu of peripheral tissues, which can cause lasting changes in immunological tone that confer disease protection or susceptibility¹. The cellular and molecular mechanisms that prompt changes in immune tone in many nonlymphoid tissues remain largely unknown. Here we find that time-limited neonatal inflammation induced by a transient reduction in neonatal regulatory T cells causes a dysregulation of subcutaneous tissue in mouse skin. This is accompanied by the selective accumulation of type 2 helper T (T_H2) cells within a distinct microanatomical niche. T_H2 cells are maintained into adulthood through interactions with a fibroblast population in skin fascia that we refer to as T_H2-interacting fascial fibroblasts (TIFFs), which expand in response to T_H2 cytokines to form subcutaneous fibrous bands. Activation of the T_H2-TIFF niche due to neonatal inflammation primes the skin for altered reparative responses to wounding. Furthermore, we identify fibroblasts in healthy human skin that express the TIFF transcriptional signature and detect these cells at high levels in eosinophilic fasciitis, an orphan disease characterized by inflammation and fibrosis of the skin fascia. Taken together, these data define a previously unidentified T_H2 cell niche in skin and functionally characterize a disease-associated fibroblast population. The results also suggest a mechanism of immunological priming whereby inflammation early in life creates networks between adaptive immune cells and stromal cells to establish an immunological set-point in tissues that is maintained throughout life.

Layilin Anchors Regulatory T Cells in Skin

Regulatory T cells (Tregs) reside in nonlymphoid tissues where they carry out unique functions. The molecular mechanisms responsible for Treg accumulation and maintenance in these tissues are relatively unknown. Using an unbiased discovery approach, we identified LAYN (layilin), a C-type lectin-like receptor, to be preferentially and highly expressed on a subset of activated Tregs in healthy and diseased human skin. Expression of layilin on Tregs was induced by TCR-mediated activation in the presence of IL-2 or TGF-β. Mice with a conditional deletion of layilin in Tregs had reduced accumulation of these cells in tumors. However, these animals somewhat paradoxically had enhanced immune regulation in the tumor microenvironment, resulting in increased tumor growth. Mechanistically, layilin expression on Tregs had a minimal effect on their activation and suppressive capacity in vitro. However, expression of this molecule resulted in a cumulative anchoring effect on Treg dynamic motility in vivo. Taken together, our results suggest a model whereby layilin facilitates Treg adhesion in skin and, in doing so, limits their suppressive capacity. These findings uncover a unique mechanism whereby reduced Treg motility acts to limit immune regulation in nonlymphoid organs and may help guide strategies to exploit this phenomenon for therapeutic benefit.

Impact of second-opinion dermatopathology reviews on surgical management of malignant neoplasms

BACKGROUND

Second-opinion review is linked to error reduction and treatment changes in anatomic pathology.

OBJECTIVE

We sought to establish the rate of diagnostic discrepancy identified by second-opinion dermatopathologic review and the effect on surgical treatment.

METHODS

Cases referred for treatment of a malignant neoplasm diagnosed by an outside pathologist were reviewed. The external and internal second-opinion dermatopathologic reports were compared. Discordance in diagnosis, subtype, and treatment change owing to second-opinion review was recorded. The referring pathologist's level of dermatopathologic training was also documented.

RESULTS

A total of 358 cases were included. Dermatopathologic second-opinion diagnosis was discordant with the outside diagnosis in 37 of 358 cases (10.3%). In 32 of 358 cases (8.9%), second-opinion review resulted in a change in treatment, with 28 of 32 (87.5%) of these changes resulting in cancelled surgery. Dermatologists without dermatopathologic fellowship training had the highest rate of discordant diagnoses compared with pathologists and dermatopathologists.

LIMITATIONS

This was a retrospective study at a tertiary care facility.

CONCLUSION

Second-opinion dermatopathologic review is associated with identification of discordant diagnoses and a substantial influence on treatment, with both cancellation of surgery and augmented management. Secondary pathologic review should be considered in high-volume surgical practices.

Effect of Topical Brimonidine on Alcohol-Induced Flushing in Asian Individuals: A Randomized Clinical Trial

Importance

Alcohol flushing syndrome (AFS, also known as Asian glow and Asian flush) affects 20% to 47% of East Asians and causes significant psychosocial distress. There are no approved treatments for this condition.

Objective

To determine whether brimonidine gel, 0.33%, decreases facial erythema in patients with AFS after consumption of alcohol.

Design, Setting, and Participants

In this randomized clinical trial, 20 healthy volunteers of East Asian descent with a self-reported history of AFS were recruited between April 2018 and March 2019.

Interventions

Participants were randomized to application of brimonidine gel to either the left or right half of their face. Placebo control was applied to the opposite side. After 30 minutes, participants ingested alcohol.

Main Outcomes and Measures

Outcomes were specified before data collection. The difference in erythema between the treated and placebo side of each participant's face was measured 60 minutes after drug application (primary outcome) and at 90 and 120 minutes after drug application (secondary outcomes). Participants were asked to rate their likelihood of using the medication again and their likelihood of recommending the medication to a friend on a scale of 0 to 10.

Results

The mean (SD) age of the 20 individuals enrolled in the study was 30.5 (8.4) years, and there were 10 women (50%). There was a significant difference in erythema at 60 minutes after drug application as measured by the difference in Clinician Erythema Assessment score (2.1; 95% CI, 1.5-2.71; P < .001) and by the difference in Subject Self-Assessment score (1.7; 95% CI, 1.1- 2.3; P < .001). This effect persisted at 90 and 120 minutes. Individuals were likely to use the medication again (7.2; 95% CI, 6.0-8.3) and would also recommend it to a friend (7.6; 95% CI, 6.5-8.6).

Conclusions and Relevance

This study demonstrates that brimonidine gel is effective in reducing the facial erythema of AFS. Patients with psychosocial distress due to AFS may benefit from treatment with brimonidine.

Trial Registration

ClinicalTrials.gov identifier: NCT03497442.

Regulatory T cells use arginase 2 to enhance their metabolic fitness in tissues

Distinct subsets of Tregs reside in nonlymphoid tissues where they mediate unique functions. To interrogate the biology of tissue Tregs in human health and disease, we phenotypically and functionally compared healthy skin Tregs with those in peripheral blood, inflamed psoriatic skin, and metastatic melanoma. The mitochondrial enzyme, arginase 2 (ARG2), was preferentially expressed in Tregs in healthy skin, increased in Tregs in metastatic melanoma, and reduced in Tregs from psoriatic skin. ARG2 enhanced Treg suppressive capacity in vitro and conferred a selective advantage for accumulation in inflamed tissues in vivo. CRISPR-mediated deletion of this gene in primary human Tregs was sufficient to skew away from a tissue Treg transcriptional signature. Notably, the inhibition of ARG2 increased mTOR signaling, whereas the overexpression of this enzyme suppressed it. Taken together, our results suggest that Tregs express ARG2 in human tissues to both regulate inflammation and enhance their metabolic fitness.

Transcriptional Programming of Normal and Inflamed Human Epidermis at Single-Cell Resolution

Perturbations in the transcriptional programs specifying epidermal differentiation cause diverse skin pathologies ranging from impaired barrier function to inflammatory skin disease. However, the global scope and organization of this complex cellular program remain undefined. Here we report single-cell RNA sequencing profiles of 92,889 human epidermal cells from 9 normal and 3 inflamed skin samples. Transcriptomics-derived keratinocyte subpopulations reflect classic epidermal strata but also sharply compartmentalize epithelial functions such as cell-cell communication, inflammation, and WNT pathway modulation. In keratinocytes, ~12% of assessed transcript expression varies in coordinate patterns, revealing undescribed gene expression programs governing epidermal homeostasis. We also identify molecular fingerprints of inflammatory skin states, including S100 activation in the interfollicular epidermis of normal scalp, enrichment of a CD1C⁺CD301A⁺ myeloid dendritic cell population in psoriatic epidermis, and IL1β^hiCCL3^hiCD14⁺ monocyte-derived macrophages enriched in foreskin. This compendium of RNA profiles provides a critical step toward elucidating epidermal diseases of development, differentiation, and inflammation.

Cheng et al. report single-cell RNA sequencing of normal and inflamed human epidermis, revealing a discrete set of specialized keratinocytes that exhibit a distinct composition at different anatomic sites. Myeloid dendritic cells and macrophages also vary sharply with epidermal anatomic site and inflammation, indicating dynamic programming of antigen-presenting cells.

The distribution of cutaneous metastases correlates with local immunologic milieu

BACKGROUND

Metastases to the skin are found with increased frequency at certain sites, such as the scalp, but the biological factors that influence this distribution are not understood.

OBJECTIVE

We aimed to compare the proportional frequency of metastases at various cutaneous locations with the immunologic microenvironments at those sites.

METHODS

We retrospectively identified all biopsy specimens of cutaneous metastases diagnosed at our institution from 1991 to 2014 (n = 1984) and mapped their anatomic distribution while controlling for regional surface area. Using a separate, mapped cohort of normal-appearing skin samples (n = 140), we measured the density of regulatory T cells, CD4(+) effector T cells, and CD8(+) T cells by flow cytometry.

RESULTS

Per unit surface area, cutaneous metastases arise most commonly on the head and neck, followed by the trunk, upper extremities, and lower extremities, respectively. Sites with more frequent metastases tend to contain a greater density of regulatory T cells and a lower proportion of CD8(+) T cells (P < .05).

LIMITATIONS

Immunologic factors were only assessed in control tissue and were not measured from patients with metastatic disease in this correlative single-center study.

CONCLUSION

The distribution of cutaneous metastases follows the distribution of regulatory and effector T cells in skin. Further studies are required to prove a mechanistic association between local immunologic factors and the development of cutaneous metastases.

Induction Hedgehog pathway inhibition followed by combined-modality radiotherapy for basal cell carcinoma

Basal cell carcinoma (BCC), the most common cancer in the U.S.A., is treated primarily with local excision. In some cases, lesion size, location or extent prevent complete resection. Locally advanced BCC responds to systemic therapy with the Hedgehog pathway inhibitor vismodegib, but withdrawal of treatment may result in disease relapse. Here we present a case of locally advanced auricular BCC treated with induction vismodegib and radiation, resulting in durable local control and an acceptable level of acute toxicity.

Transcription restores DNA repair to heterochromatin, determining regional mutation rates in cancer genomes

Somatic mutations in cancer are more frequent in heterochromatic and late-replicating regions of the genome. We report that regional disparities in mutation density are virtually abolished within transcriptionally silent genomic regions of cutaneous squamous cell carcinomas (cSCCs) arising in an XPC(-/-) background. XPC(-/-) cells lack global genome nucleotide excision repair (GG-NER), thus establishing differential access of DNA repair machinery within chromatin-rich regions of the genome as the primary cause for the regional disparity. Strikingly, we find that increasing levels of transcription reduce mutation prevalence on both strands of gene bodies embedded within H3K9me3-dense regions, and only to those levels observed in H3K9me3-sparse regions, also in an XPC-dependent manner. Therefore, transcription appears to reduce mutation prevalence specifically by relieving the constraints imposed by chromatin structure on DNA repair. We model this relationship among transcription, chromatin state, and DNA repair, revealing a new, personalized determinant of cancer risk.

Memory regulatory T cells reside in human skin

Regulatory T cells (Tregs), which are characterized by expression of the transcription factor Foxp3, are a dynamic and heterogeneous population of cells that control immune responses and prevent autoimmunity. We recently identified a subset of Tregs in murine skin with properties typical of memory cells and defined this population as memory Tregs (mTregs). Due to the importance of these cells in regulating tissue inflammation in mice, we analyzed this cell population in humans and found that almost all Tregs in normal skin had an activated memory phenotype. Compared with mTregs in peripheral blood, cutaneous mTregs had unique cell surface marker expression and cytokine production. In normal human skin, mTregs preferentially localized to hair follicles and were more abundant in skin with high hair density. Sequence comparison of TCRs from conventional memory T helper cells and mTregs isolated from skin revealed little homology between the two cell populations, suggesting that they recognize different antigens. Under steady-state conditions, mTregs were nonmigratory and relatively unresponsive; however, in inflamed skin from psoriasis patients, mTregs expanded, were highly proliferative, and produced low levels of IL-17. Taken together, these results identify a subset of Tregs that stably resides in human skin and suggest that these cells are qualitatively defective in inflammatory skin disease.

Temporal dissection of tumorigenesis in primary cancers

Timely intervention for cancer requires knowledge of its earliest genetic aberrations. Sequencing of tumors and their metastases reveals numerous abnormalities occurring late in progression. A means to temporally order aberrations in a single cancer, rather than inferring them from serially acquired samples, would define changes preceding even clinically evident disease. We integrate DNA sequence and copy number information to reconstruct the order of abnormalities as individual tumors evolve for 2 separate cancer types. We detect vast, unreported expansion of simple mutations sharply demarcated by recombinative loss of the second copy of TP53 in cutaneous squamous cell carcinomas (cSCC) and serous ovarian adenocarcinomas, in the former surpassing 50 mutations per megabase. In cSCCs, we also report diverse secondary mutations in known and novel oncogenic pathways, illustrating how such expanded mutagenesis directly promotes malignant progression. These results reframe paradigms in which TP53 mutation is required later, to bypass senescence induced by driver oncogenes.

Transcriptional profiling of the dose response: a more powerful approach for characterizing drug activities

The dose response curve is the gold standard for measuring the effect of a drug treatment, but is rarely used in genomic scale transcriptional profiling due to perceived obstacles of cost and analysis. One barrier to examining transcriptional dose responses is that existing methods for microarray data analysis can identify patterns, but provide no quantitative pharmacological information. We developed analytical methods that identify transcripts responsive to dose, calculate classical pharmacological parameters such as the EC50, and enable an in-depth analysis of coordinated dose-dependent treatment effects. The approach was applied to a transcriptional profiling study that evaluated four kinase inhibitors (imatinib, nilotinib, dasatinib and PD0325901) across a six-logarithm dose range, using 12 arrays per compound. The transcript responses proved a powerful means to characterize and compare the compounds: the distribution of EC50 values for the transcriptome was linked to specific targets, dose-dependent effects on cellular processes were identified using automated pathway analysis, and a connection was seen between EC50s in standard cellular assays and transcriptional EC50s. Our approach greatly enriches the information that can be obtained from standard transcriptional profiling technology. Moreover, these methods are automated, robust to non-optimized assays, and could be applied to other sources of quantitative data.

Chondrodermatitis nodularis chronica helicis in monozygotic twins

Chondrodermatitis nodularis chronica helicis (CNCH) is a benign inflammatory nodule of the helix. Patients report severe tenderness upon pressure. Commonly seen in middle-aged men, there are no reports of this disease in twins. We report middle-aged male monozygotic twins who simultaneously developed CNCH. This suggests, but does not prove, the possibility of a hereditary factor in the pathogenesis of CNCH.

Bleeding complications in dermatologic surgery

Although the overall incidence is low, bleeding complications in dermatologic surgery can occur and be the source of significant patient morbidity. In this article, we summarize the key aspects of preoperative assessment of patients at risk for bleeding. A review of current issues and literature regarding safe continuation of anticoagulant and antiplatelet medications in dermatologic surgery patients is also presented. In addition, principles for management of bleeding events, should they occur, are also highlighted.

Basal cell carcinomas arising within multiple trichoepitheliomas

Although trichoepitheliomas (TEs) are commonly regarded as benign tumors of follicular origin, the natural history of multiple familial trichoepitheliomas (MFT) and their risk for malignancy has been unclear. We describe a 57-year-old male with numerous skin-colored firm papules and plaques present on the central face since 6 years of age. Recently, some lesions had enlarged and ulcerated. Other family members were similarly affected. Biopsies from multiple lesions showed TEs both alone and associated with basal cell carcinoma (BCC) in the same section, suggesting the secondary development of BCCs within TEs. Many prior reports of BCCs arising within TEs in patients with presumed MFT were likely misdiagnosed cases of nevoid BCC. This report is a compelling example of MFT in which BCCs evolved secondarily. Awareness of the potential for the evolution of carcinoma in patients with MFT is important in the management of these patients.

Persistent delayed-type hypersensitivity reaction to injectable non-animal-stabilized hyaluronic acid

OBJECTIVE

Injectable hyaluronic acid is a glycosaminoglycan used for soft-tissue augmentation. A number of products that are not Food and Drug Administration (FDA) approved for use in the United States are used commonly in Europe. We report a case of persistent delayed-type hypersensitivity to injected non-animal-stabilized hyaluronic acid. The patient was initially injected in Europe with a non-FDA-approved filler but traveled to the United States for evaluation of this adverse reaction.

METHODS

A case of adverse reaction to non-animal-stabilized hyaluronic acid is described. An overview of selected hyaluronic acid filler products is provided.

RESULTS

The patient developed persistent facial edema after injection of hyaluronic acid filler to the melolabial folds, glabella, lips, and perioral rhytids.

CONCLUSION

Injectable hyaluronic acid can be associated with a variety of complications including immediate and delayed-type hypersensitivity reactions. Physicians should be familiar with products used in other countries, as patients may present for evaluation following adverse reaction to fillers obtained abroad or from American physicians using non-FDA-approved products.

Diagnosis and Treatment of Pigmentary Disorders in Asian Skin

Individuals of Asian heritage are predisposed to congenital and acquired pigmentary disorders. Cosmetic enhancement is frequently the primary treatment goal for these benign lesions. Accurate diagnosis of the nature of the pigmentary disorder is fundamental for administering safe and effective therapy. Before the advent of modern laser technology, such reported treatments as cryotherapy, dermabrasion, chemical peeling, and surgical excision resulted in unpredictable results. This article focuses on the diagnosis of disorders of pigmentation in Asian patients and reviews laser and light treatment modalities.

Bleeding Complications in Dermatologic Surgery

Although the overall incidence is low, bleeding complications in dermatologic surgery can occur and be the source of significant patient morbidity. In this article, we summarize the key aspects of preoperative assessment of patients at risk for bleeding. A review of current issues and literature regarding safe continuation of anticoagulant and antiplatelet medications in dermatologic surgery patients is also presented. In addition, principles for management of bleeding events, should they occur, are also highlighted.

Infectious Complications and Antibiotic Use in Dermatologic Surgery

Infection rates in dermatologic surgery are low, ranging on average from 1 to 3%. Studies have shown that many practitioners likely overuse antibiotics, both for prevention of wound infection and in endocarditis prophylaxis. This article discusses patient and environmental risk factors in would infection. Data on wound infection prophylaxis are reviewed, and specific guidelines set forth with regards to appropriate antibiotic usage, drug selection, dosage, and timing. In addition, recommendations surrounding endocarditis and prosthetic joint infection prophylaxis are presented as they apply to dermatologic surgery.

Seborrheic keratosis with basal clear cells: A distinctive microscopic mimic of melanoma in situ

BACKGROUND

We observed seborrheic keratoses with many basilar clear cells, creating a microscopic pattern that mimicked a seborrheic keratosis involved by melanoma in situ.

OBJECTIVE

We sought to report a series of these seborrheic keratoses and the immunohistochemical stains used to reach a proper diagnosis.

METHODS

We reviewed 9 cases of seborrheic keratosis that had a distinctive pattern of basal clear cells with ample cytoplasm. All cases were evaluated by conventional microscopy, and Melan-A, S-100, and high molecular weight keratin 903 immunostains.

RESULTS

The basal clear cells failed to react with Melan-A and S-100 protein antisera. In contrast, these cells labeled with an antikeratin antibody in all cases. In all, 7/9 (78%) showed immunopositivity only at the peripheries of cells, creating a pattern that could be mistaken for a negative stain if not examined at high magnification.

LIMITATIONS

This is a retrospective review of cases limited to a large referral dermatopathology service.

CONCLUSIONS

We describe a previously uncharacterized pattern of seborrheic keratosis that can microscopically mimic melanoma in situ. Careful conventional microscopy coupled with a panel of immunostains can allow the proper diagnosis to be reached.

Practical retinoid chemoprophylaxis in solid organ transplant recipients

Solid organ transplant recipients are at a significantly increased risk of developing skin cancer. Both systemic and topical retinoids are useful for chemosuppression of skin cancer in this patient population. These drugs can reduce both the present extent and the future development of premalignant and malignant skin lesions. This paper reviews the current data on the chemoprophylactic properties of topical and systemic retinoids. A practical guide for their use in organ transplant recipients is provided. Specific recommendations for implementing and maintaining therapy, as well as appropriate management and monitoring of adverse events, are presented.

Hypopigmented mycosis fungoides in childhood and adolescence

We present a case of purely hypopigmented mycosis fungoides of 8-years duration in an 18-year-old woman who responded readily to psoralen plus ultraviolet A (PUVA) treatment. The literature pertaining to hypopigmented mycosis fungoides is reviewed.

The "hired gun" effect: assessing the effect of pay, frequency of testifying, and credentials on the perception of expert testimony

Three experiments addressed the proposition that jurors use short cuts in processing information when confronted with expert scientific testimony. The results of the first two studies demonstrated that experts who are highly paid for their testimony and who testify frequently are perceived as "hired guns." They are neither liked nor believed. The results of the third experiment replicated the hired gun effect and showed that it is most likely to occur when the testimony is complex and cannot be easily processed. The results were discussed in terms of the theoretical differences between central and peripheral processing of persuasive messages in a legal context.

Balanitis xerotica obliterans and its differential diagnosis

BACKGROUND

Balanitis xerotica obliterans is a subcategory of lichen sclerosus et atrophicus limited to the male genitalia and is associated with destructive inflammation, phimosis, urethral stenosis, and squamous cell carcinoma.

METHODS

The medical literature was searched from 1983-1998 using key words balanitis, lichen, and sclerosis using the MEDLINE system.

RESULTS AND CONCLUSIONS

Balanitis xerotica obliterans can be distinguished from other genital dermatoses with similar characteristics through patient history, clinical findings, and laboratory evaluation.. Tzanck smear and cutaneous biopsy, along with a rapid protein reagin test, will provide a definitive diagnosis. Treatment with high-dose topical corticosteroids relieves symptoms, and therapy focuses on prevention of disease progression.

Gender differences in glycosylated hemoglobin levels in seasonal affective disorder patients and controls

Seasonal affective disorder (SAD) has been shown to manifest different symptoms in female and male patients. Specifically, women with SAD have been shown to have greater increases in overeating, weight gain, and increased sleep as compared with their male counterparts. Given these dietary changes, we predicted that female SAD patients would exhibit increased glycosylated hemoglobin (HbA1) levels, indicative of chronically elevated glucose levels. Twenty-two patients (15 women and seven men) and matched controls were enrolled during the winter season and tested for HbA1 levels. A three-way analysis of variance (ANOVA; gender x group x season) was insignificant and the result was a negative study. After the initial hypothesis was rejected, we undertook a post-hoc analysis of the data, from which emerged that in winter, women patients had higher HbA1 levels as compared with matched controls. As our original hypothesis was rejected, we cannot accept the results of the post-hoc study. However, numerous other studies have demonstrated that female and male SAD patients differ in their pathophysiology, and are suggestive that in future analyses ought to consider analyzing subjects separately across gender.

Efficient localization of mutations by interval haplotype analysis

We have developed a mathematical algorithm to implement a method for localizing mutations using haplotype analysis. Our strategy infers haplotypes based on the determination of genotypes of a proximal and a distal marker for 21 chromosomal intervals distributed across the mouse genome (corresponding to two intervals for Chromosomes (Chrs) 1 and 2 and one for the remaining 17 autosomes). To simulate the analysis of mice homozygous for recessive mutations, we tested the efficacy of our method on over 200 data sets generated from two independent mapping panel data sets containing the genotypes of 46 F2 progeny of an intercross and 94 F2 progeny of a backcross. In all cases we were able to identify the chromosomal interval carrying the recessive mutation despite the fact that some of the data sets consisted of as few as 10 meioses. Our strategy proved sensitive and expedient, since the simulated genome-wide screen could be executed by genotype analysis of 40 microsatellite markers in small numbers of intercross or backcross progeny.

Mutations of the noncoding region of the connexin32 gene in X-linked dominant Charcot-Marie-Tooth neuropathy

We studied two families with X-linked dominant Charcot-Marie-Tooth neuropathy. The clinical findings included onset around age 14 years, with moderate weakness of feet extensors and palmar and dorsal interossei, areflexia, distal hypesthesia, and slow progressivity. Motor nerve conduction velocities showed slowing (20 to 30 m/sec) and EMGs were normal. Genetic linkage analysis revealed positive lod scores with the markers of the Xq13.1 region in family 2, but was noninformative in family 1. There were no point mutations in the connexin32 gene coding region. Instead, family 1 revealed a T-to-G transversion at position -528 relative to the ATG start codon, whereas family 2 showed a C-to-T transition at position -458. The first mutation is located in the nerve-specific connexin32 promoter just upstream of the transcription start site, the second is located in the 5' untranslated region of the mRNA.

The human connexin32 gene is transcribed from two tissue-specific promoters

The connexin32 (cx32) gene codes for the gap junction protein found in liver, pancreas and nervous tissue. Recently mutations in the coding region of this gene have been associated with the dominant X-linked form of Charcot-Marie-Tooth (CMTX1) neuropathy. Since some CMTX1 patients show no mutations in their cx32 gene coding region, it was speculated that these patients carry mutations in the promoter region of the gene. This paper describes the organization of the human cx32 gene and its tissue-specific transcription. The gene consists of three exons that are alternatively spliced to produce mRNAs with different 5'-untranslated regions (UTRs). Transcription is initiated from two tissue-specific promoters. In liver and pancreas, promoter P1, located more than 8 kb upstream of the translation start codon, is used, and the transcript is processed to remove a large intron. In contrast, in nerve cells, transcription is initiated from promoter P2, located 497 bp upstream from the translation start codon, and the transcript is processed to remove a small 355-pb intron. The downstream exon, which includes the entire coding sequence, is shared by both mRNAs. CMTX1 patients with a normal cx32 coding region are expected to have mutations in this newly described promoter P2 rather than the known promoter P1.

Use of alternate promoters for tissue-specific expression of the gene coding for connexin32

The promoter of rat connexin32 (Cx32), the gap junction protein found in liver, was studied in transgenic mice. Cx32 transgenes, containing 2.5-kb of sequence upstream from the promoter, exon I, the entire 6.1-kb intron and the beginning of the coding sequence linked to the gene encoding luciferase (Luc), were found to be expressed in mouse in the same tissue-specific manner as previously reported for Cx32. Another construct lacking the promoter, but retaining 1.8 kb from the 3' end of the intron, was found to be expressed specifically in the nervous system. This result suggested that a second promoter, different from that used in liver, functions in nervous tissue. The use of this promoter in normal rats was corroborated by sequence analysis of reverse-transcribed PCR products obtained from rat nervous tissue RNA. The second promoter drives the synthesis of a second Cx32 mRNA species that is processed to remove a small 345-bp intron that shares its acceptor splice site with the large intron. This finding could have implications for the genetic basis of the X-linked form of Charcot-Marie-Tooth disease (CMT-X) in those patients that do not exhibit mutations in the Cx32-coding region.