Keratinocytic Nevus Research Articles

Epidermal Nevi and Related Syndromes — Part 1: Keratinocytic Nevi

Epidermal nevi are hamartomatous lesions derived from the epidermis and/or adnexal structures of the skin; they have traditionally been classified according to their morphology. New variants have been described in recent years and advances in genetics have contributed to better characterization of these lesions and an improved understanding of their relationship with certain extracutaneous manifestations. In the first part of this review article, we will look at nevi derived specifically from the epidermis and associated syndromes.

Epilepsy in Neurological Phenotypes of Epidermal Nevus Syndrome

Epidermal nevus syndrome (ENS) encompasses a group of congenital genetic disorders characterized by the association of an epidermal nevus with systemic anomalies including the brain. The most frequent subtype with neurological features is <i>linear sebaceous nevus syndrome</i> (LSNS), followed by keratinocytic nevus syndrome (ENS). Both are caused by postzygotic <i>RAS</i> mutations. All forms of ENS are mosaic disorders that share a common embryological basis and pathogenesis as <i>neurocristopathies</i>. The lines of Blaschko indicate the cutaneous migratory pathways of neural crest. Neural crest defects explain the development of nevi and associated multisystemic anomalies: brain, ocular, osseous, muscular, orodental, cardiovascular, endocrine, renal/urinary, and adipose tissue. Epilepsy and cognitive and motor deficits are caused mainly by hemimegalencephaly (HME), a closely related mosaic anomaly caused by somatic mutations in PI3K–AKT3–mTOR pathway that determines overgrowth. The usual onset of epilepsy is in the neonatal period or early infancy, often as infantile spasms. The pioneer description of nevus sebaceous in 1895 by Jadassohn is the basis for delineating the LSNS. The eponym “Schimmelpenning syndrome” as a substitute for that long-established term makes no sense in the context of the large number of authors who contributed to defining this syndrome. A review of 111 cases of LSNS and other subtypes enabled a classification of neurological phenotypes; epilepsy occurred in 77% and HME in 38%. Three distinctive additional syndromes also are within the spectrum of ENS: CLOVES, SCALP, and Heide's syndrome. The impact of epilepsy in patients affected by ENS is related to time of onset and extent of brain anomalies. Timing of the mutation determines the phenotype and severity of the systemic lesions.

Chapter 2 - Phenotype/genotype correlations in epidermal nevus syndrome as a neurocristopathy

Epidermal nevus syndrome (ENS) is a term that encompasses several phenotypes defined by the association of an epidermal nevus with one or more congenital systemic anomalies, mainly ocular, osseous and cerebral. The two most frequent, keratinocytic nevus syndrome and linear sebaceous nevus syndrome, also correspond to the neurological phenotypes. They both exhibit overlapping and distinctive features but same etiology: post-zygotic mosaic mutations in RAS genes. Their pathogenesis is due to defective neural crest, further confirming that they are the same basic entity contradicting the concept that they are a group of heterogeneous syndromes with different etiologies. Both have been reported for more than a century. The sebaceous nevus, hallmark of linear sebaceous nevus syndrome, was defined by Jadassohn in 1895; the large number of subsequent contributors in defining this syndrome precludes the introduction of eponyms. Three other distinctive phenotypes within the spectrum of ENS with CNS involvement are CLOVES, SCALP and Heide's syndromes. Recognition of neurological phenotypes with multisystemic involvement should invoke multidisciplinary investigation and management. In some ENS phenotypes the association of melanocytic nevi with keratinocytic and sebaceous nevi, all sharing RAS mutations, predicts multisystemic involvement, in particular severe rickets and osseous anomalies. Phenotype is, therefore, the starting point for clinicians to guide genetic, neurological and other systemic investigations for patient management. The most frequent brain malformation in neurological phenotypes of ENS is hemimegalencephaly (HME). Epilepsy is the most frequent neurological symptom, in particular infantile spasms, with or without HME. The impact of neurological and systemic manifestations is related to onset and extent of the mutations. Timing of the mutation determines phenotype and severity. Proteus syndrome is a neurological phenotype of epidermal keratinocytic nevus syndrome not an independent, separate syndrome.

Vascular malformation and common keratinocytic nevus of the soft type: phacomatosis pigmentovascularis revisited.

Phacomatosis pigmentovascularis is a rare syndrome characterized by the coexistence of a pigmented nevus and a cutaneous vascular malformation. We report a 5-year-old boy with all the typical findings of phacomatosis pigmentovascularis type Ia. Although its existence according to the traditional classification has been questioned, this case represents a very rare association of a capillary vascular malformation and a common keratinocytic nevus of the soft type.

Familial Papular Epidermal Nevus with “Skyline” Basal Cell Layer

Papular epidermal nevus with "skyline" basal cell layer (PENS), a novel keratinocytic nevus, has recently been described as a mosaic condition with varying presentations. We herein describe typical PENS lesions, which usually occur sporadically, affecting two members of the same family. The concept of paradominant inheritance is proposed to explain the paradox of occasional transmission of normally sporadically occurring traits.

Papular Epidermal Nevus with “Skyline” Basal Cell Layer (PENS) Following a Blaschko Linear Pattern

Papular epidermal nevus with "skyline" basal cell layer (PENS), a variant of epidermal nevi, has recently been described as a small, round or polygonal papule, visible at birth or shortly thereafter, with characteristic histopathologic features. It has been considered a separate entity from keratinocytic nevi because no lesion observed thus far has followed any of the known archetypical mosaic patterns. Here we describe for the first time a PENS lesion following a linear distribution pattern along Blaschko's lines.

Nevus Sebaceus Is a Mosaic RASopathy

The recent discovery that nevus sebaceus is a mosaic RASopathy represents a major breakthrough in research on epidermal nevi. In this issue, both Levinsohn et al. and Sun et al. confirm this advancement with results obtained through whole-exome sequencing. Further molecular studies will almost certainly show that sebaceous and keratinocytic nevi are different disorders, although there is some clinical overlap.

Systemic epidermal nevus with involvement of the oral mucosa due to FGFR3mutation

BackgroundEpidermal nevi (EN) represent benign congenital skin lesions following the lines of Blaschko. They result from genetic mosaicism, and activating FGFR3 and PIK3CA mutations have been implicated.Case presentationWe report a female patient with a systemic keratinocytic nevus also involving the oral mucosa. Molecular genetic analysis revealed a mosaicism of the FGFR3 hotspot mutation R248C in the EN lesions of the skin and of the oral mucosa. The detection of the R248C mutation in a proportion of blood leukocytes and a slight scoliosis suggest an EN syndrome.ConclusionsOur results show that activating FGFR3 mutations can also affect the oral mucosa and that extracutaneous manifestations of EN syndrome can be subtle. We highlight the theoretical risk of the patient having an offspring with thanatophoric dysplasia as gonadal mosaicism for the R248C mutation cannot be excluded.

Papular epidermal nevus with “skyline” basal cell layer (PENS)

Several types of epidermal keratinocytic nevus are recognized. We sought to describe a previously unreported keratinocytic nevus with distinctive clinical and histopathologic features in 5 patients. We performed a clinical and photographic review, and obtained skin biopsy samples for histopathologic examination from each patient. Genetic analysis to screen for fibroblast growth factor receptor 3 and phosphatidylinositol 3-kinase, catalytic, alpha hotspot mutations was performed on lesional skin from two patients. Five infants (2 male, 3 female) had from 1 to 11 lesions present since birth. These consisted of 1- to 7-mm hyperkeratotic papules with a rough, flat surface and a round, commalike, rectangular, or polygonal shape. Histopathologic examination showed acanthosis with broad and rectangular rete ridges, and strikingly arranged basal cells with palisaded nuclei. Genetic testing on paraffin-embedded specimens from two patients ruled out hotspot mutations in the fibroblast growth factor receptor 3 and phosphatidylinositol 3-kinase, catalytic, alpha genes. A small number of patients are presented. We propose the name "papular epidermal nevus with 'skyline' basal cell layer" (PENS) for this newly recognized condition.

Epidermal Nevus Syndromes: Clinical Findings in 35 Patients

Of the patients with epidermal nevi, 10-18% may have disorders of the eye, nervous, and musculoskeletal systems. A predisposition to malignant neoplasms in ectodermal and mesodermal structures may also be found. There are six different epidermal nevus syndromes described so far: Proteus, congenital hemidysplasia with ichthyosiform nevus and limb defect syndrome, phakomatosis pigmentokeratotica, sebaceous nevus, Becker nevus, and nevus comedonicus. Thirty-five patients with epidermal nevus syndrome seen at the National Institute of Pediatrics in Mexico City during a 31-year period are described. This syndrome represented 7.9% of 443 patients with epidermal nevi; its relative frequency was 1 case per 11,928 pediatric patients and 1 case per 1080 dermatologic patients. Nine epidermal nevus syndrome patients (26%) had Proteus syndrome. Sebaceous nevus syndrome was found in six patients (17%), while the nevus comedonicus syndrome was found in three (8%). Two patients were diagnosed with phakomatosis pigmentokeratotica and one patient with congenital hemidysplasia with ichthyosiform nevus and limb defect syndrome. This is the first report of phakomatosis pigmentokeratotica and congenital hemidysplasia with ichthyosiform nevus and limb defect syndrome in Mexican patients. One patient had an inflammatory linear verrucous epidermal nevus with systemic involvement. Thirteen patients (37%) had keratinocytic nevi with systemic involvement. We propose the keratinocytic nevus syndrome to be defined as the association of a keratinocytic nevus with neuronal migration and/or musculoskeletal disorders in addition to a higher risk for mesodermal neoplasms.