Microphthalmia-associated transcription factor regulates RAB27A gene expression and controls melanosome transport.

Melanosomes are lysosome-related organelles specialized in melanin synthesis and transport. In this study, we show that microphthalmia-associated transcription factor (MITF) silencing induces melanosome gathering around the nucleus and causes the relocalization of Rab27A, Slac2a-Mlph, and Myo5a that control the transport of melanosomes on the actin network. In an attempt to elucidate the mechanism by which MITF controls melanosome distribution, we identify RAB27A as a new MITF target gene. Indeed, MITF silencing leads to a dramatic decrease in Rab27A expression and blocks the stimulation of Rab27A expression evoked by cAMP. Further, forced expression of MITF increases Rab27A expression, indicating that MITF is required and sufficient for Rab27A expression in melanoma cells. MITF binds to two E-boxes in the proximal region of the Rab27A promoter and stimulates its transcriptional activity. Finally, re-expression of Rab27A, in MITF-depleted cells, restores the transport of melanosomes to the cell periphery. These results show that RAB27A is a new direct transcriptional target of MITF and link MITF to melanosome transport, another key parameter of melanocyte differentiation and skin pigmentation. Interestingly, Rab27A is involved in other fundamental physiological functions, such as the transport of lytic granules and insulin secretion. Thus our results, deciphering the mechanism of Rab27A transcriptional regulation, have an interest that goes beyond the skin pigmentation field

Prevalence of inherited ichthyosis in France: a study using capture-recapture method

International audienceBACKGROUND:Inherited ichthyoses represent a group of rare skin disorders characterized by scaling, hyperkeratosis and inconstant erythema, involving most of the tegument. Epidemiology remains poorly described. This study aims to evaluate the prevalence of inherited ichthyosis (excluding very mild forms) and its different clinical forms in France.METHODS:Capture - recapture method was used for this study. According to statistical requirements, 3 different lists (reference/competence centres, French association of patients with ichthyosis and internet network) were used to record such patients. The study was conducted in 5 areas during a closed period.RESULTS:The prevalence was estimated at 13.3 per million people (/M) (CI95%, [10.9 - 17.6]). With regard to autosomal recessive congenital ichthyosis, the prevalence was estimated at 7/M (CI 95% [5.7 - 9.2]), with a prevalence of lamellar ichthyosis and congenital ichthyosiform erythroderma of 4.5/M (CI 95% [3.7 - 5.9]) and 1.9/M (CI 95% [1.6 - 2.6]), respectively. Prevalence of keratinopathic forms was estimated at 1.1/M (CI 95% [0.9 - 1.5]). Prevalence of syndromic forms (all clinical forms together) was estimated at 1.9/M (CI 95% [1.6 - 2.6]).CONCLUSIONS:Our results constitute a crucial basis to properly size the necessary health measures that are required to improve patient care and design further clinical studies

Mosaic Activating Mutations in GNA11 and GNAQ Are Associated with Phakomatosis Pigmentovascularis and Extensive Dermal Melanocytosis.

Common birthmarks can be an indicator of underlying genetic disease but are often overlooked. Mongolian blue spots (dermal melanocytosis) are usually localized and transient, but they can be extensive, permanent, and associated with extracutaneous abnormalities. Co-occurrence with vascular birthmarks defines a subtype of phakomatosis pigmentovascularis, a group of syndromes associated with neurovascular, ophthalmological, overgrowth, and malignant complications. Here, we discover that extensive dermal melanocytosis and phakomatosis pigmentovascularis are associated with activating mutations in GNA11 and GNAQ, genes that encode Gα subunits of heterotrimeric G proteins. The mutations were detected at very low levels in affected tissues but were undetectable in the blood, indicating that these conditions are postzygotic mosaic disorders. In vitro expression of mutant GNA11(R183C) and GNA11(Q209L) in human cell lines demonstrated activation of the downstream p38 MAPK signaling pathway and the p38, JNK, and ERK pathways, respectively. Transgenic mosaic zebrafish models expressing mutant GNA11(R183C) under promoter mitfa developed extensive dermal melanocytosis recapitulating the human phenotype. Phakomatosis pigmentovascularis and extensive dermal melanocytosis are therefore diagnoses in the group of mosaic heterotrimeric G-protein disorders, joining McCune-Albright and Sturge-Weber syndromes. These findings will allow accurate clinical and molecular diagnosis of this subset of common birthmarks, thereby identifying infants at risk for serious complications, and provide novel therapeutic opportunities

A Solve-RD ClinVar-based reanalysis of 1522 index cases from ERN-ITHACA reveals common pitfalls and misinterpretations in exome sequencing

Purpose Within the Solve-RD project (https://solve-rd.eu/), the European Reference Network for Intellectual disability, TeleHealth, Autism and Congenital Anomalies aimed to investigate whether a reanalysis of exomes from unsolved cases based on ClinVar annotations could establish additional diagnoses. We present the results of the “ClinVar low-hanging fruit” reanalysis, reasons for the failure of previous analyses, and lessons learned. Methods Data from the first 3576 exomes (1522 probands and 2054 relatives) collected from European Reference Network for Intellectual disability, TeleHealth, Autism and Congenital Anomalies was reanalyzed by the Solve-RD consortium by evaluating for the presence of single-nucleotide variant, and small insertions and deletions already reported as (likely) pathogenic in ClinVar. Variants were filtered according to frequency, genotype, and mode of inheritance and reinterpreted. Results We identified causal variants in 59 cases (3.9%), 50 of them also raised by other approaches and 9 leading to new diagnoses, highlighting interpretation challenges: variants in genes not known to be involved in human disease at the time of the first analysis, misleading genotypes, or variants undetected by local pipelines (variants in off-target regions, low quality filters, low allelic balance, or high frequency). Conclusion The “ClinVar low-hanging fruit” analysis represents an effective, fast, and easy approach to recover causal variants from exome sequencing data, herewith contributing to the reduction of the diagnostic deadlock

RAB27A et CTNS (de la pathologie à la physiologie pigmentaire)

Le rôle principal des mélanocytes est de synthétiser de la mélanine dans les mélanosomes puis de les transférer aux kératinocytes pour les protéger des effets mutagènes des ultraviolets. De nombreux gènes sont impliqués dans ce processus dont RAB27A et CTNS mutés respectivement dans le syndrome de Griscelli-Prunieras type 2 (SG2) et la cystinose infantile. RAB27A, une GTPase recrute à la surface des mélanosomes, via la mélanophiline, le moteur moléculaire MyosineVa ce qui permet leur transport distal le long du réseau d actine. Au cours de ce travail j ai caractérisé les défauts moléculaires de 3 patients atteints de SG2 ayant une mutation faux sens homozygote de RAB27A aboutissant à une transition W73G, L130P et A152P. J ai ensuite montré que le transport actine-dépendant des mélanosomes est stimulé par l a-MSH via l AMPc. Cette stimulation passe à court terme par les protéines p21Rho et ROCK et par une augmentation de l interaction de la mélanophiline avec l actine et à long terme par la stimulation de Rab27a. Enfin j ai montré que le transport actine-dépendant des mélanosomes est régulé par MITF via essentiellement la régulation de RAB27A. Cette régulation est directe et constitue le principal mode de régulation du transport de mélanosomes. La cystinosine est un co-transporteur lysosomal de cystine/H+ dont le rôle dans les mélanocytes est inconnu. J ai montré que la cystinosine est une protéine lysosomale et que son inhibition bloque la pigmentation induite par l AMPc suite à une augmentation de la dégradation de la tyrosinase et une acidification du mélanosome. Par ailleurs l expression de Ctns est régulée par l AMPc, probablement par le biais de MITF.NICE-BU Sciences (060882101) / SudocSudocFranceF

Etude clinique de l'atteinte cutanée dans la cystinose infantile

NICE-BU Médecine Odontologie (060882102) / SudocSudocFranceF

Syndrome de Griscelli-Prunieras par mutation du gène de Rab27a (type 2) (étude des mécanismes moléculaires chez 3 patients)

NICE-BU Médecine Odontologie (060882102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

PW02-012 - First clinical description of an infant with DITRA

International audienc

Alitretinoin reduces erythema in inherited ichthyosis

Abstract Background Acitretin is the main retinoid used to treat severe inherited ichthyosis. Alternatives may be considered if it results ineffective or there are side-effects, or for women of childbearing age. Our objective is evaluation of the effects and tolerance of alitretinoin. An observational retrospective multicentric study was designed to analyse patients with inherited ichthyosis treated by alitretinoin. Results A total of 13 patients were included, 11 of whom were receiving acitretin at inclusion. The main reason for switching to alitretinoin was a desire for pregnancy, but also because of side-effects or unsatisfactory efficacy. Starting dose was 10 mg/day, increased to 20 or 30 mg/day. Alitretinoin seemed to be more effective than acitretin at reducing erythema, but was less effective at reducing scaling or hyperkeratosis. Global efficacy was considered low for two patients, moderate for nine, and high for two. Treatment was well-tolerated, except for one patient who presented with benign intracranial hypertension leading to discontinuation of treatment. Conclusions Alitretinoin may be suitable for hereditary ichthyosis with prominent erythema, especially for women of childbearing age