Incontinentia pigmenti Stage 1 is not simply vesiculo-bullous but vesiculo-pustular.

Incontinentia pigmenti (IP) is a rare X-linked dominant, male-lethal disorder characterized by pathognomic skin lesions. As described in the literature the typical cutaneous changes follow the pattern of Blaschko's lines and develop in four stages that usually start at birth. Stage 1 is called vesicular, bullous or inflammatory. The vesicles are rapidly filled with eosinophils and thus turn into pustules. Thus, the term "pustular" is relevant to the first phase of IP, and the stage can be considered as "vesiculopustular/inflammatory" to be more precise than "vesicular" or "bullous."

What is in a name-Perifollicular fibroma or fibrofolliculoma?

So far, confusion exists regarding the question of whether hereditary perifollicular fibromas and fibrofolliculomas can be distinguished from each other. Here, histopathological arguments are presented to clarify this terminological problem. In 1977, Birt et al. described a large kindred affected with hereditary multiple "fibrofolliculomas," which they thought were "a hitherto unrecognized pilar hamartoma," but they never claimed the fibrofolliculomas were part of a syndrome. A careful microscopic comparison shows, however, that the tumors are clinically and histopathologically identical to perifollicular fibromas, as first described by Burnier and Rejsek in 1925. Their familial occurrence was discovered in 1971 by Civatte and Le Tréguilly. Before 1977, the term "perifollicular fibroma" was used for these skin tumors. By contrast, Hornstein and Knickenberg described in 1975 perifollicular fibromas as a cutaneous marker of a syndrome characterized by a predisposition to colon cancer and pneumothorax. Later, two French groups erroneously proposed the term "Birt-Hogg-Dubé syndrome" to describe the co-occurrence of fibrofolliculomas, trichodiscomas, and acrochordons, which was contrary to what Birt et al. had in mind. Hence, today, we should discriminate between the hereditary nonsyndromic perifollicular fibromas, as documented by Civatte and Le Tréguilly and later by Birt et al., and the syndromic perifollicular fibromas, as delineated by Hornstein and Knickenberg.

Superimposed Mosaicism in the Form of Extremely Extended Segmental Plexiform Neurofibroma Caused by a Novel Pathogenic Variant in the NF1 Gene.

Plexiform neurofibromas occurring in approximately 20-50% of all neurofibromatosis type-1 (NF1) cases are histologically benign tumors, but they can be fatal due to compression of vital structures or transformation to malignant sarcomas or malignant peripheral nerve sheath tumors. All sizeable plexiform neurofibromas are thought to result from an early second mutation giving rise to a loss of heterozygosity of the NF1 gene. In this unusual case, a 12-year-old girl presented with a rapidly growing, extremely extensive plexiform neurofibroma with segmental distribution over the entire right arm, extending to the right chest wall and mediastinum, superimposed on classic cutaneous lesions of NF1. After several surgical interventions, the patient was efficiently treated with an oral selective MEK inhibitor, selumetinib, which resulted in a rapid reduction of the tumor volume. Molecular analysis of the NF1 gene revealed a c.2326-2 A>G splice-site mutation in the clinically unaffected skin, peripheral blood sample, and plexiform neurofibroma, which explains the general clinical symptoms. Furthermore, a novel likely pathogenic variant, c.4933dupC (p.Leu1645Profs*7), has been identified exclusively in the girl's plexiform neurofibromas. This second-hit mutation can explain the extremely extensive segmental involvement.

Autosomal dominant genodermatoses in adults being heralded by superimposed skin lesions in children.

In autosomal dominant skin disorders, pronounced mosaic involvement may sometimes occur in the neonate, originating in a heterozygous embryo from early loss of heterozygosity, probably during the first week after fertilization. In biallelic phenotypes, such overlaying mosaic involvement may coexist with disseminated mosaicism, for example, in neurofibromatosis or tuberous sclerosis. In other phenotypes, however, classical nonsegmental involvement tends to appear much later, which is why the superimposed mosaic is a heralding feature. In Brooke-Spiegler syndrome (eccrine cylindromatosis), a large pedigree documented a 5-year-old boy with multiple, congenital small eccrine cylindromas along the lines of Blaschko. Disseminated cylindromas were absent because they usually appear in adulthood. ̶ In Hornstein-Knickenberg syndrome, an affected woman had an 8-year-old son with a nevus comedonicus-like lesion exemplifying a forerunner of the syndrome. ("Birt-Hogg-Dubé syndrome" represents a nonsyndromic type of hereditary perifollicular fibromas.) In glomangiomatosis, neonatal superimposed mosaicism is a heralding feature because disseminated lesions appear during puberty or adulthood. Linear porokeratosis is a harbinger of disseminated porokeratosis that develops 30 or 40 years later. ̶ Cases of superimposed linear Darier disease were forerunners of nonsegmental manifestation. ̶ In a case of Hailey-Hailey disease, neonatal mosaic lesions heralded nonsegmental involvement that began 22 years later.

[Update on nevi and nevoid skin disorders]. / Neues über Nävi und nävoide Hauterkrankungen.

Autosomal dominant transmission with sex-limited manifestation represents a previously unrecognized mode of inheritance. The white lentiginosis of Grosshans exclusively occurs in females, whereas male gene carriers remain clinically unaffected but can transmit the underlying mutation to their offspring. There are some other examples: Hereditary bilateral lymphedema of the CELSR1 type that only occurs in females, too. Unlike common sebaceous nevus (HRAS or KRAS mutations), cerebriform sebaceous nevus is caused by a postzygotic lethal FGFR2 mutation. Cutis marmorata telangiectatica congenita and reticular capillary nevus have previously been considered one single entity. Today, their dichotomy is proven at the molecular level. It is important to be aware of the new port-wine nevus of the AKT3 type because this anomaly may constitute a cutaneous marker of severe congenital brain defects. The newly described transient abdominal telangiectasia in newborns can easily be mistaken as a capillary nevus, but represents an innocuous neonatal phenomenon that spontaneously fades away within the first three months.

Phacomatosis spilosebacea: A new name for a distinctive binary genodermatosis.

Phacomatosis pigmentokeratotica (PPK) is defined by the association of papular nevus spilus arranged in a flag-like pattern and sebaceous nevus following Blaschko's lines. A systematic search of the worldwide literature retrieved 95 well-established PPK cases. An additional 30 cases were excluded for a number of reasons. Based on this study, we propose to rename PPK phacomatosis spilosebacea (PSS). Mosaic mutations of the HRAS gene are the only proven cause of PSS. The extracutaneous abnormalities of PSS result from various degrees of intermingling of Schimmelpenning syndrome and papular nevus spilus syndrome. PSS seems to be a condition at particularly high risk of developing basal cell carcinoma, urogenital malignancies, and vitamin D-resistant hypophosphatemic rickets. Extracutaneous abnormalities were detected in approximately 75% of PSS cases.

Autosomal dominant inheritance with sex-limited manifestation: An unusual mode of transmission in humans and animals.

Autosomal dominant, sex-limited inheritance is a distinct mode of transmission that should not be conflated with X-linked inheritance. From animal studies, we know that sex-limited inheritance implies the chance to "turn off" some genes in either males or females, in order to meliorate the phenotype, for example, by improving the fecundity. In this way, sex-limited genes play an important role in the evolution of diverse species of animals. In human genetics, however, the biological significance of sex-limited genes is unknown until today. When screening the literature, we found, thus far, three human examples of sex-limited transmission. Autosomal dominant, male-limited inheritance has meticulously been studied in a particular form of precocious puberty. Limitation to females was described in autosomal dominant lymphedema of the CESLR1 type, being underpinned by convincing molecular findings. Another example is white lentiginosis of Grosshans that shows clinical evidence of such mode of transmission although molecular findings are lacking as yet. In the animal kingdom, autosomal dominant sex-limited inheritance is a well-established phenomenon that has extensively been studied in various species such as butterflies, damselflies, fish (cichlids), and birds. Hence, at this point in time, it seems likely that other human examples of this mode of inheritance have previously been reported or will be published in the future.

PTPN11 Mosaicism Causes a Spectrum of Pigmentary and Vascular Neurocutaneous Disorders and Predisposes to Melanoma.

Phakomatosis pigmentovascularis is a diagnosis that denotes the coexistence of pigmentary and vascular birthmarks of specific types, accompanied by variable multisystem involvement, including CNS disease, asymmetrical growth, and a predisposition to malignancy. Using a tight phenotypic group and high-depth next-generation sequencing of affected tissues, we discover here clonal mosaic variants in gene PTPN11 encoding SHP2 phosphatase as a cause of phakomatosis pigmentovascularis type III or spilorosea. Within an individual, the same variant is found in distinct pigmentary and vascular birthmarks and is undetectable in blood. We go on to show that the same variants can cause either the pigmentary or vascular phenotypes alone, and drive melanoma development within pigmentary lesions. Protein structure modeling highlights that although variants lead to loss of function at the level of the phosphatase domain, resultant conformational changes promote longer ligand binding. In vitro modeling of the missense variants confirms downstream MAPK pathway overactivation and widespread disruption of human endothelial cell angiogenesis. Importantly, patients with PTPN11 mosaicism theoretically risk passing on the variant to their children as the germline RASopathy Noonan syndrome with lentigines. These findings improve our understanding of the pathogenesis and biology of nevus spilus and capillary malformation syndromes, paving the way for better clinical management.

Superimposed mosaicism in cutaneous sarcoidosis: A hypothesis.

Sarcoidosis is a chronic granulomatous disorder affecting the lungs, skin, and many other organs. Twin studies suggest that genetic factors account, to a large degree, for the etiology of the disorder. Hence, theoretically, we could postulate that the phenomenon of superimposed mosaicism in the form of a pronounced segmental involvement, overlaying the disseminated non-segmental lesions, should also occur in sarcoidosis. Indeed, one case suggesting superimposed mosaicism in cutaneous sarcoidosis was found in the literature and is reassessed here.

Cutis marmorata telangiectatica congenita being caused by postzygotic GNA11 mutations.

Cutis marmorata telangiectatica congenita (CMTC) is characterized by coarse-meshed capillary malformations arranged in asymmetrically distributed patches. The disorder may be associated with hyper- or hypoplastic limbs, syndactyly, cleft palate, and glaucoma. Because the disease usually occurs sporadically, the concept of a lethal mutation surviving by mosaicism was proposed about 30 years ago. Here we describe three children with CMTC due to a postzygotic GNA11 mutation c547C > T (p.Arg183Cys), documented in saliva (patient 1) or lesional cutaneous tissue (patients 2 and 3). All three individuals had widespread and asymmetric CMTC which was present from birth and became fainter during the first years of life. Variably associated anomalies included glaucoma, choroidal capillary malformation, and body asymmetry. In previous case reports, postzygotic GNA11 mutations were documented in two cases of phacomatosis cesiomarmorata, being characterized by CMTC coexisting with segmental dermal melanocytosis. Moreover, postzygotic GNA11 mutations were noted in two CMTC patients described under the incorrect diagnosis of "nevus vascularis mixtus". Hence, the present cases convincingly support the concept that CMTC can be caused by mosaic GNA11 mutations and thus belongs to the GNA11-Related Capillary Nevus (GNARCAN) spectrum. In two other bona fide cases of CMTC, however, we were unable to find a mutation in GNA11, which may be explained either by our inability to detect a very low percentage of mutant cells or by genetic heterogeneity of the phenotype.

Conradi-Hünermann-Happle syndrome with minimal signs.

A 4-year-old girl presented with congenital patches of scalp alopecia, which on physical examination, was consistent with blaschkolinear alopecic patches with mild epidermal atrophy. Similar atrophic hypopigmented patches were seen on the trunk and proximal extremities. With the clinical suspicion of Conradi-Hünermann-Happle syndrome, genetic testing was performed and revealed a mutation in the EBP gene. Despite characteristic cutaneous findings, no skeletal, ocular, or other anomalies were found on further evaluation.

Progressive Osseous Heteroplasia is not an Autosomal Dominant Trait but Reflects Superimposed Mosaicism in Different GNAS Inactivation Disorders.

Progressive osseous heteroplasia (POH) is a rarely occurring genetic condition characterized by severe segmental ossification involving the skin and deep connective tissues including the muscles. So far, the disorder is generally described as an autosomal dominant trait. By contrast, the following arguments are in favor of the alternative concept that POH should rather be taken as a non-specific segmental manifestation of different GNAS inactivation disorders such as Albright hereditary osteodystrophy (AHO) with hormone resistance, AHO without hormone resistance, and osteomatosis cutis. Presently, POH has got its own OMIM number 166350 but this is obviously wrong because the disorder does not reflect heterozygosity for a GNAS mutation. Conversely, the disorder is most likely due to an early event of postzygotic loss of heterozygosity with loss of the corresponding wild-type allele. This alternative concept, as proposed in 2016, offers a plausible explanation for the following features of POH. Familial occurrence is usually absent. POH is usually observed in families with one of the three GNAS inactivation disorders as mentioned above. Mosaicism is suggested by the pronounced segmental manifestation of POH and by its lateralization. Some patients have, in addition to POH, bilaterally disseminated features of osteomatosis cutis or AHO, and other patients have family members with one of these nonsegmental disorders. Remarkably, POH tends to appear much earlier than the nonsegmental GNAS inactivation disorders. - Molecular support of the concept was documented in a superficial variant of POH called 'plate-like osteoma cutis'. In several other autosomal dominant skin disorders, molecular corroboration of the theory of superimposed mosaicism has been provided. - For all of these reasons, it is unlikely that POH can further be taken as a distinct autosomal dominant trait. Generation of more molecular data in multiple cases of POH occurring in GNAS inactivation disorders will be crucial to corroborate the proposed concept.

Porokeratosis Plantaris, Palmaris et Disseminata Caused by Con- genital Pathogenic Variants in the MVD Gene and Loss of Hetero-zygosity in Affected Skin.

Porokeratoses are a heterogeneous group of keratinization disorders. For linear porokeratosis and disseminated superficial actinic porokeratosis, a heterozygous pathogenic germline variant in a mevalonate pathway gene and a postzygotic second hit mutation present in affected skin have been shown to be the patho-genetic mechanism for the development of the lesions. However, the molecular mechanism leading to development of porokeratosis plantaris, palmaris et disseminata is not known. This study analysed a cohort of 4 patients with linear porokeratosis and 3 patients with porokeratosis plantaris, palmaris et disseminata, and performed mutation analyses of DNA extracted from blood samples and skin biopsies. All of the study patients carried the heterozygous germline variant c.70+5G>A in the MVD gene. Loss of heterozygosity due to a second hit mutation was found in affected skin of 3 patients with linear porokeratosis and 2 patients with porokeratosis plantaris, palmaris et disseminata. These results suggest that porokeratosis plantaris, palmaris et disseminata shares the same pathogenetic mechanism as other porokeratosis subtypes and belongs to the phenotypic spectrum of MVD-associated porokeratosis.