E. Estève

Pharmacologic and Functional Characterization of Malignant Hyperthermia in the R163C RyR1 Knock-in Mouse

Background:Malignant hyperthermia is a pharmacogenetic disorder affecting humans, dogs, pigs, and horses. In the majority of human cases and all cases in animals, malignant hyperthermia has been associated with missense mutations in the skeletal ryanodine receptor (RyR1). Methods:The authors used a “knock-in” targeting vector to create mice carrying the RyR1 R163C malignant hyperthermia mutation. Results:Validation of this new mouse model of human malignant hyperthermia susceptibility includes (1) proof of transcription of the R163C allele and expression of ryanodine receptor protein in R163C heterozygous and R163C homozygous animals; (2) fulminant malignant hyperthermia episodes in R163C heterozygous mice after exposure to 1.25–1.75% halothane or an ambient temperature of 42°C characterized by increased rectal temperature, respiratory rate, and inspiratory effort, with significant blood biochemical changes indicating metabolic acidosis, ending in death and hyperacute rigor mortis; (3) intraperitoneal pretreatment with dantrolene provided 100% protection from the halothane-triggered fulminant malignant hyperthermia episode; (4) significantly increased sensitivity (decreased effective concentration causing 50% of the maximal response) of R163C heterozygous and homozygous myotubes to caffeine, 4-chloro-m-cresol, and K+-induced depolarization; (5) R163C heterozygous and homozygous myotubes have a significantly increased resting intracellular Ca2+ concentration compared with wild type; (6) R163C heterozygous sarcoplasmic reticulum membranes have a twofold higher affinity (Kd = 35.4 nm) for [3H]ryanodine binding compared with wild type (Kd = 80.1 nm) and a diminished inhibitory regulation by Mg2+. Conclusions:Heterozygous R163C mice represent a valid model for studying the mechanisms that cause the human malignant hyperthermia syndrome.

Clinical variants of the preprotuberant stage of dermatofibrosarcoma protuberans.

Background  Some cases of dermatofibrosarcoma protuberans (DFSP) do not protrude above the skin.

COEXISTENT CUTANEOUS T-CELL LYMPHOMA AND B-CELL MALIGNANCY

BACKGROUND The coexistence of cutaneous T-cell lymphoma (CTCL) and a B-cell malignancy (BCM) is rare. OBJECTIVE Our aim was to assess the clinical and pathologic aspects of coexistent CTCL and BCM and to examine potential explanations for this association. METHODS We report six cases of concurrent CTCL and BCM in which B- and T-cell lineages were demonstrated by immunologic studies. The literature includes 13 additional cases. All 19 CTCL-BCM cases are reviewed. RESULTS CTCL either preceded or followed the BCM, which was a low-grade malignancy in most cases (16 of 19). Possible explanations for the association include a genetic predisposition, underlying viral infection, chemotherapy-induced carcinogenesis, stimulation of a B-cell clone by malignant helper T cells, and alterations in progenitor cells before determination of B- and T-cell lineage. CONCLUSION An alteration in progenitor cells, with subsequent oncogenic activation of variable origin, might account for most cases of coexistent CTCL and BCM.

A malignant hyperthermia–inducing mutation in RYR1 (R163C): alterations in Ca2+ entry, release, and retrograde signaling to the DHPR

Bidirectional signaling between the sarcolemmal L-type Ca2+ channel (1,4-dihydropyridine receptor [DHPR]) and the sarcoplasmic reticulum (SR) Ca2+ release channel (type 1 ryanodine receptor [RYR1]) of skeletal muscle is essential for excitation–contraction coupling (ECC) and is a well-understood prototype of conformational coupling. Mutations in either channel alter coupling fidelity and with an added pharmacologic stimulus or stress can trigger malignant hyperthermia (MH). In this study, we measured the response of wild-type (WT), heterozygous (Het), or homozygous (Hom) RYR1-R163C knock-in mouse myotubes to maintained K+ depolarization. The new findings are: (a) For all three genotypes, Ca2+ transients decay during prolonged depolarization, and this decay is not a consequence of SR depletion or RYR1 inactivation. (b) The R163C mutation retards the decay rate with a rank order WT > Het > Hom. (c) The removal of external Ca2+ or the addition of Ca2+ entry blockers (nifedipine, SKF96365, and Ni2+) enhanced the rate of decay in all genotypes. (d) When Ca2+ entry is blocked, the decay rates are slower for Hom and Het than WT, indicating that the rate of inactivation of ECC is affected by the R163C mutation and is genotype dependent (WT > Het > Hom). (e) Reduced ECC inactivation in Het and Hom myotubes was shown directly using two identical K+ depolarizations separated by varying time intervals. These data suggest that conformational changes induced by the R163C MH mutation alter the retrograde signal that is sent from RYR1 to the DHPR, delaying the inactivation of the DHPR voltage sensor.

Childhood‐onset psoriasis: association with future cardiovascular and metabolic comorbidities

Psoriasis is associated with higher prevalences of cardiovascular and metabolic comorbidities in adults but the relationship of age at onset and those prevalences is unknown.

Combined treatment with low‐dose methotrexate and initial short‐term superpotent topical steroids in bullous pemphigoid: an open, multicentre, retrospective study

Background  The interest of long‐term superpotent topical steroids (STS) in bullous pemphigoid (BP) has been supported by randomized controlled trials. However, inadequate compliance, poor cutaneous tolerance and nursing difficulties are potential drawbacks. Open‐label studies on limited series of patients suggested that low‐dose methotrexate (MTX) may be useful, permitting long‐term maintenance of a clinical remission obtained by initial, short‐term STS.

No correlation between the molecular subtype of COL1A1-PDGFB fusion gene and the clinico-histopathological features of dermatofibrosarcoma protuberans.

TO THE EDITOR Dermatofibrosarcoma protuberans (DFSP) is a dermal tumor of intermediate malignancy. Propensity for metastases is low but local recurrence risk is high unless a wide surgical excision is performed. In addition to the classical presentation of DFSP, several clinical and histological variants have been described, such as DFSP-containing fibrosarcomatous areas or malignant fibrous histiocytoma areas, Bednar tumor, giant cell fibroblastoma, and superficial adult fibrosarcoma (Simon et al., 1997; Sheng et al., 2001; Maire et al., 2002a; Sirvent et al., 2003; Bianchini et al., 2007; Szollosi et al., 2007). DFSP and related tumors are molecularly characterized by the presence of an abnormal chimeric gene that fuses COL1A1 (17q21.3) with platelet-derived growth factor-B chain (PDGFB) (22q13.1) (Simon et al., 1997). The detection of COL1A1– PDGFB is mandatory in case of unusual clinical or histological presentation, as well as in pediatric cases (Sirvent et al., 2003; Bianchini et al., 2007; Maire et al., 2007). A striking feature of COL1A1–PDGFB fusion consists of the high variability of the break point location between the exons 6 and 49 of COL1A1 (Sirvent et al., 2003; Bianchini et al., 2007). In contrast, the break point in PDGFB is consistently located in the first intron. We have investigated whether the COL1A1 break point location is associated with clinical or histological features. In such a case, the precise detection of the COL1A1 break point detection by using multiplex reverse transcriptase–PCR and sequencing could be useful for diagnosis or evaluation of prognosis. For this purpose we compiled a series of 172 DFSP cases with both molecular and clinico-histological data (Supplementary Table S1), including (i) 35 cases of DFSP or related tumors addressed for molecular diagnosis referral to the laboratory of Solid Tumors Genetics (Nice, France) from nine different French Hospitals and previously unreported; (ii) 22 DFSP cases previously published by our group (Pedeutour et al., 1994, 1995, 1996; Simon et al., 1997; Greco et al., 1998; Navarro et al., 1998; Maire et al., 2002a, b, c, 2007; Terrier-Lacombe et al., 2003; Jouary et al., 2007); (iii) 115 cases published between 1997 and 2008 (O’Brien et al., 1998; Wang et al., 1999, 2000; Vanni et al., 2000; Sheng et al., 2001; Gokden et al., 2003; Sandberg et al., 2003; Sirvent et al., 2003; Saeki et al., 2003a, b, 2005, 2006; Martin et al., 2005; Craver et al., 2006; Kashima et al., 2006; Llombart et al., 2006, 2008; Nakanishi et al., 2007; Szollosi et al., 2007; Takahira et al., 2007; Patel et al., 2008). The description of the clinical and histological features of the 172 cases is compiled in Supplementary Table S1. Continuous data (age, tumor size) were described with mean, SD, and range (minimum–maximum); nominal scale data (gender, anatomic location, histological variant) were described by frequencies and relative frequencies (expressed as percentage). A Fisher exact test showed no significant differences in terms of gender, clinical presentation, and histological variant between our series and tumors studied by other groups (Table 1). Similarly, an unpaired Student’s t-test showed no significant differences in the two series in terms of tumor size. In contrast, a slight difference between the two series was observed for the anatomic location and the mean age. The first could be explained by reports of exceptional anatomical locations in the literature, and the later by a more frequent recruitment of pediatric patients in our laboratory. The very high variability of the COL1A1 break point position was confirmed, as 38 different COL1A1 exons have been identified. The most frequently rearranged COL1A1 exons were exon 25 (n1⁄4 19), 32 (n1⁄418), and 47 (n1⁄4 15) (Figure 1). A standard analysis of variance of the COL1A1 break point position with respect to the clinico-histological parameters was performed by grouping the break points into four distinct groups of 11 exons each (group A: exons 6–16; group B: exons 17–27; group C: exons 28–38; and group D: exons 39–49). The following parameters were tested for the COL1A1 break point position: age, histological variant, anatomic location, and gender. None of the parameters tested showed a significant association with the either group. Only the anatomic location showed a slight trend, P1⁄40.01843 (Supplementary Table S2). Also, no significant correlation between the most represented COL1A1 break points (n45) (exons 7, 25, 29, 32, 33–34, 40, 42, 46, and 47) and clinical or histological features was observed. This result is consistent with the role of the COL1A1 side of the fusion gene as a simple cis element for PDGFB overexpression (Greco et al., 1998; Simon et al., 2001). The spectacular clinical effect of tyrosine kinase receptor inhibitor (imatinib mesylate) also supports the major role of the PDGFR activation through the overexpression of PDGFB Abbreviations: COL1A1, collagen type I-a 1; DFSP, dermatofibrosarcoma protuberans; PDGFB, plateletderived growth factor-B chain

Prognostic value of antibodies to Merkel cell polyomavirus T antigens and VP1 protein in patients with Merkel cell carcinoma.

Merkel cell polyomavirus (MCPyV) is the main aetiological agent of Merkel cell carcinoma (MCC). Serum antibodies against the major MCPyV capsid protein (VP1) are detected in the general population, whereas antibodies against MCPyV oncoproteins (T antigens) have been reported specifically in patients with MCC.

A malignant hyperthermia-inducing mutation in RYR1 (R163C): consequent alterations in the functional properties of DHPR channels.

Bidirectional communication between the 1,4-dihydropyridine receptor (DHPR) in the plasma membrane and the type 1 ryanodine receptor (RYR1) in the sarcoplasmic reticulum (SR) is responsible for both skeletal-type excitation–contraction coupling (voltage-gated Ca2+ release from the SR) and increased amplitude of L-type Ca2+ current via the DHPR. Because the DHPR and RYR1 are functionally coupled, mutations in RYR1 that are linked to malignant hyperthermia (MH) may affect DHPR activity. For this reason, we investigated whether cultured myotubes originating from mice carrying an MH-linked mutation in RYR1 (R163C) had altered voltage-gated Ca2+ release from the SR, membrane-bound charge movement, and/or L-type Ca2+ current. In myotubes homozygous (Hom) for the R163C mutation, voltage-gated Ca2+ release from the SR was substantially reduced and shifted (∼10 mV) to more hyperpolarizing potentials compared with wild-type (WT) myotubes. Intramembrane charge movements of both Hom and heterozygous (Het) myotubes displayed hyperpolarizing shifts similar to that observed in voltage-gated SR Ca2+ release. The current–voltage relationships for L-type currents in both Hom and Het myotubes were also shifted to more hyperpolarizing potentials (∼7 and 5 mV, respectively). Compared with WT myotubes, Het and Hom myotubes both displayed a greater sensitivity to the L-type channel agonist ±Bay K 8644 (10 µM). In general, L-type currents in WT, Het, and Hom myotubes inactivated modestly after 30-s prepulses to −50, −10, 0, 10, 20, and 30 mV. However, L-type currents in Hom myotubes displayed a hyperpolarizing shift in inactivation relative to L-type currents in either WT or Het myotubes. Our present results indicate that mutations in RYR1 can alter DHPR activity and raise the possibility that this altered DHPR function may contribute to MH episodes.

Syndrome babouin associé à une polysensibilisation aux corticoïdes

Resume Introduction Le syndrome babouin est une forme d’eczema liee a la prise d’un allergene par voie systemique. Nous rapportons le cas exceptionnel d’un malade qui a eu un syndrome babouin suite a la prise per os de betamethasone. Observation Un homme de 58 ans a consulte pour un eczema du perinee, des fesses et des aisselles. Il s’agissait cliniquement d’un syndrome babouin. Un traitement per os par la betamethasone (Celestene ® ) pris 48 heures plus tot etait le principal suspect. Ce malade avait ete traite par de nombreux dermocorticoides depuis de nombreuses annees. Les tests epicutanes ont confirme une sensibilisation a la betamethasone. Cette exploration a aussi mis en evidence une sensibilisation aux quatre classes de corticoides. L’arret prolonge de tout corticoide a amene une amelioration tres nette de son eczema. Discussion Le syndrome babouin chez ce malade etait le symptome d’un eczema systemique a la betamethasone. L’utilisation de differents dermocorticoides a entraine une polysensibilisation aux corticoides. Le malade s’etait sensibilise par voie percutanee. La tres nette amelioration du malade a l’arret des corticoides a ete un argument fort de pertinence de cette polysensibilisation. Il n’a pas ete possible de conseiller un corticoide sans danger pour ce malade.