Nevus comedonicus syndrome: a case associated with multiple basal cell carcinomas and a rudimentary toe

Acne Syndromes and Mosaicism

Abnormal mosaicism is the coexistence of cells with at least two genotypes, by the time of birth, in an individual derived from a single zygote, which leads to a disease phenotype. Somatic mosaicism can be further categorized into segmental mosaicism and nonsegmental somatic mosaicism. Acne is a chronic illness characterized by inflammatory changes around and in the pilosebaceous units, commonly due to hormone- and inflammatory signaling-mediated factors. Several systemic disorders, such as congenital adrenal hyperplasia, polycystic ovarian syndrome, and seborrhoea-acne-hirsutism-androgenetic alopecia syndrome have classically been associated with acne. Autoinflammatory syndromes, including PAPA, PASH, PAPASH, PsAPASH, PsaPSASH, PASS, and SAPHO syndromes include acneiform lesions as a key manifestation. Mosaic germline mutations in the FGFR2 gene have been associated with Apert syndrome and nevus comedonicus, two illnesses that are accompanied by acneiform lesions. In this review, we summarize the concept of cutaneous mosaicism and elaborate on acne syndromes, as well as acneiform mosaicism.

Happle-Tinschert Syndrome: A Case Report of Unilateral Segmentally Arranged Basaloid Follicular Hamartoma with Scoliosis and Review of Literature

Happle-Tinschert syndrome is a rare disease characterized by unilateral, segmentally arranged basaloid follicular hamartoma (BFH) with osseous, dental, and cerebral anomalies. Although BFH has been demonstrated to be associated with mutations in the patched gene, the genetic basis for Happle-Tinschert syndrome is still unknown. We describe a case of Happle-Tinschert syndrome in a 26-year-old female. The patient presented with unilateral skin color change to brownish papules and atrophoderma following the development of Blaschko's lines, plantar pitting, and nail dystrophy on the right side of the body. She also had scoliosis, hemihypotrophy, and dental anomalies. The skin lesions were histologically confirmed as BFHs. Next-generation sequencing of the patient's genomic DNA obtained from a peripheral blood sample identified no pathogenic mutation. This case illustrates the characteristic clinical features of Happle-Tinschert syndrome. Thus far, 14 cases of Happle-Tinschert syndrome have been reported, and we report another case of this syndrome.

Nevus comedonicus syndrome: A systematic review of the literature

Nevus comedonicus (NC) syndrome is a condition first identified in 1978. The cause of NC syndrome has been recently proven to be a gain-of-function, mosaic postzygotic mutation of the NEK9 gene. A systematic review of the literature retrieved 43 well-established cases of NC syndrome reported so far. Three morphological variants of NC in NC syndrome emerged: (a) the more common, predominantly comedonal type; (b) "Selhorst type"; and (c) "atrophoderma vermiculatum" type. NC syndrome is mainly associated with ocular, skeletal, and neural abnormalities, most typically ipsilateral congenital cataract and malformations of fingers and toes.

Further delineation of the phenotypic spectrum of nevus comedonicus syndrome to include congenital pulmonary airway malformation of the lung and aneurysm

Nevus comedonicus syndrome (NCS) is a rare epidermal nevus syndrome characterized by ocular, skeletal, and central nervous system anomalies. We present a 23-month-old boy with a history of a congenital pulmonary airway malformation (CPAM) of the lung and a congenital cataract who developed progressive linear and curvilinear plaques of dilated follicular openings with keratin plugs (comedones) on parts of his scalp, face, and body consistent with nevus comedonicus. MRI of the brain demonstrated an aneurysm of the right internal carotid artery. Genetic testing identified NEK9 c.1755_1757del (p.Thr586del) at mean allele frequency of 28% in the nevus comedonicus. This same mutation was present in the CPAM tissue. This is the first case of a CPAM in a patient with an epidermal nevus syndrome. This case expands the phenotype of nevus comedonicus syndrome to include CPAM and vascular anomalies.

Happle-Tinschert, Curry-Jones and segmental basal cell naevus syndromes, overlapping disorders caused by somatic mutations in hedgehog signalling genes: the mosaic hedgehog spectrum

Happle-Tinschert syndrome (HTS) and Curry-Jones syndrome (CJS; OMIM 601707) are rare, sporadic, multisystem disorders characterized by hypo- and hyperpigmented skin patches following Blaschko's lines, plus acral skeletal and other abnormalities. The blaschkoid pattern implies mosaicism, and indeed CJS was found in 2016 to be caused by a recurrent postzygotic mutation in a gene of the hedgehog signalling pathway, namely SMO, c.1234C>T, p.Leu412Phe. More recently the original case of HTS was found to carry the same somatic mutation. Despite this genetic and phenotypic overlap, two significant differences remained between the two syndromes. The histological hallmark of HTS, basaloid follicular hamartomas, is not a feature of CJS. Meanwhile, the severe gastrointestinal manifestations regularly reported in CJS had not been described in HTS. We report a patient whose phenotype was entirely consistent with HTS apart from intractable constipation, and a second patient with classic features of CJS plus early-onset medulloblastoma, a feature of basal cell naevus syndrome (BCNS). Both had the same recurrent SMO mutation. This prompted a literature review that revealed a case with the same somatic mutation, with basaloid follicular hamartomas and other features of both CJS and BCNS. Segmental BCNS can also be caused by a somatic mutation in PTCH1. We thus demonstrate for the first time phenotypic and genetic overlap between HTS, CJS and segmental BCNS. All of these conditions are caused by somatic mutations in genes of the hedgehog signalling pathway and we therefore propose the unifying term 'mosaic hedgehog spectrum'. What's already known about this topic? Happle-Tinschert syndrome (HTS) and Curry-Jones syndrome (CJS) are rare mosaic multisystem disorders with linear skin lesions. CJS is characterized by severe constipation, which has not previously been reported in HTS. HTS is characterized by basaloid follicular hamartomas, which are not a recognized feature of CJS. The recurrent mosaic SMO mutation found in CJS was recently reported in a patient with HTS. What does this study add? We describe a patient with HTS and intractable constipation, and a case of CJS with medulloblastoma. Both patients had the same recurrent somatic SMO mutation also found in a case reported as segmental basal cell naevus syndrome. SMO functions in the hedgehog pathway, explaining phenotypic overlap between HTS, CJS and mosaic basal cell naevus syndrome. We propose the term 'mosaic hedgehog spectrum' for these overlapping conditions.

[Histopathological study of basaloid follicular hamartoma]

INTRODUCTION

Basaloid follicular hamartoma (BFH) is a rare tumor first described in 1985. It bears clinical and histologic similarities with basal cell carcinoma (BCC), in particular the so-called infundibulocystic form. We performed a single-center clinicopathological study of a series of typical cases of this entity that is occasionally difficult to diagnose.

MATERIALS AND METHODS

All cases of BFH seen at the Dermatopathology Laboratory of Strasbourg University Hospital were included and analyzed by means of HE staining and Ber-EP4 and PHLDA1 immunolabelling. Diagnosis was made in the event of basaloid proliferation with anastomosing cords developed from a hair follicle. Clinical data were collected from clinical files.

RESULTS

We identified 15 cases in 13 patients of mean age 44.8 years (range: 4 to 90) and the sex-ratio was 5/8. Lesions consisted of flesh-colored papules measuring 0.3 to 1.2cm in diameter, without any preferential site. Three patients had multiple lesions consisting of several coalescent papules on a breast for one, sparse papules on the back for another, and hundreds of linear unilateral BFHs, associated with osseous abnormalities, characteristic of Happle-Tinschert syndrome, for the third. All tumors were limited to the superficial and mid dermis, with a vertical orientation and connection to the epidermis in 14 of the 15 patients. In some cases, the outermost cells were basophilic while the central cells were eosinophilic. Peripheral palisading and clefting were frequently observed. Keratin cysts or sebaceous ducts were consistently present, indicating follicular differentiation. Ber-EP4+ cells were restricted to the periphery of the cords and PHLDA1 was weakly expressed.

DISCUSSION

BFH is a rare entity that must be differentiated from BCC. It presents as solitary or multiple lesions, either grouped in plaques or with a generalized or linear unilateral distribution. Generalized BFH may be associated with autoimmune diseases and linear unilateral BFH with osseous, dental and cerebral abnormalities in Happle-Tinschert syndrome. It is important to distinguish BFH from BCC to avoid inappropriate aggressive treatment.

Nevus Comedonicus Syndrome

A case of nevus comedonicus syndrome with atypical cutaneous presentation (widespread involvement without any particular pattern, midline lesions involving lower abdomen and involvement of bilateral pinna), and some unusual skeletal (adduction deformity involving bilateral metatarsal along with medial deviation at the level of tarsometatarsal joint), central nervous system (agenesis of corpus callosum with a interhemispheric cyst), visceral (pancreatic cyst) and neurological manifestations have been illustrated.

Epidermal nevus syndromes

The term epidermal nevus syndrome (ENS) has been used to describe the association of epidermal hamartomas and extracutaneous abnormalities. Although many continue to use the term "ENS," it is now understood that this is not one disease, but rather a heterogeneous group with distinct genetic profiles defined by a common cutaneous phenotype: the presence of epidermal and adnexal hamartomas that are associated with other organ system involvement. One commonality is that epidermal nevi often follow the lines of Blaschko and it appears the more widespread the cutaneous manifestations, the greater the risk for extracutaneous manifestations. The majority of the extracutaneous manifestations involve the brain, eye, and skeletal systems. The CNS involvement is wide ranging and involves both clinical manifestations such as intellectual disability and seizures, as well as structural anomalies. Several subsets of ENS with characteristic features have been delineated including the nevus sebaceus syndrome, Proteus syndrome, CHILD syndrome, Becker's nevus syndrome, nevus comedonicus syndrome, and phakomatosis pigmentokeratotica. Advances in molecular biology have revealed that the manifestations of ENS are due to genomic mosaicism. It is likely that the varied clinical manifestations of ENS are due in great part to the functional effects of specific genetic defects. Optimal management of the patient with ENS involves an interdisciplinary approach given the potential for multisystem involvement. Of note, epidermal nevi have been associated with both benign and malignant neoplasms, and thus ongoing clinical follow-up is required.

Nevus comedonicus in oral-facial-digital syndrome type 1: a new finding or overlapping syndromes?

We report a patient with oral-facial-digital syndrome type 1 (OFDS1) who exhibited features overlapping those of nevus comedonicus syndrome, an unusual presentation that may potentially represent a new variant of OFDS1. OFDS1 and nevus comedonicus syndrome represent two rare syndromes with numerous overlapping features that have yet to be described in relation to one another. The features present in our patient led us to propose the possibility of a new variant of OFDS1 in which nevus comedonicus represents a cutaneous manifestation of the syndrome. Knowledge of this potential relationship is important for identification and management of the syndromes' accompanying manifestations in affected patients and may offer further insight into crossroads of pathogenesis.

Nevus comedonicus: an updated review

The intention of this review on nevus comedonicus (NC) is to update on clinical features, pathogenesis, and therapy. NC is a rare epidermal nevus type. It is part of the nevus comedonicus syndrome, a neurocutaneous disorder with ocular, skeletal, and central nervous symptoms. Recently, acne-related signaling pathways and somatic mutations of tyrosine kinase receptors have been identified and may play a role in NC pathogenesis. On preexistent NC secondary skin tumors can develop, which are often benign. Treatment options of NC include topical therapy, laser, and surgery.

Congenital systematized basaloid follicular hamartoma with microphthalmia and hemimegalencephaly

The lines of Blaschko are a cutaneous pattern of mosaicism present in a variety of skin disorders. Developmental abnormalities affecting other tissues derived from the embryonic ectoderm and mesoderm are sometimes associated. Here, we describe a 5-year-old boy with basaloid follicular hamartoma affecting the left side of the body in linear multiple bands, following Blaschko lines. Lesions were predominantly hypopigmented macules and streaks, but among these, we could observe brownish atrophic patches and brown papules. Furthermore, ipsilateral hemimegaloencephaly and microphthalmia were present. These findings suggest a neurocutaneous condition recently described by Happle and Tinschert. Its nosologic classification will be discussed.

Epidermal nevi

Nevi or nests of cells may be made up of a variety of cell types. The cell types that live in the epidermis include epidermal cells or keratinocytes, sebaceous glands, hair follicles, apocrine and eccrine glands, and smooth muscle cells. This article discusses epidermal or keratinocyte nevi, nevus sebaceous, nevus comedonicus, smooth muscle hamartomas, and inflammatory linear verrucous epidermal nevi. Syndromes associated with epidermal nevi are also reviewed.

The group of epidermal nevus syndromes Part I. Well defined phenotypes

The epidermal nevus syndromes represent a group of distinct disorders that can be distinguished by the type of associated epidermal nevus and by the criterion of presence or absence of heritability. Well defined syndromes characterized by organoid epidermal nevi include Schimmelpenning syndrome, phacomatosis pigmentokeratotica, nevus comedonicus syndrome, angora hair nevus syndrome, and Becker nevus syndrome. The molecular basis of these disorders has so far not been identified. By contrast, the group of syndromes characterized by keratinocytic nevi comprises three phenotypes with a known molecular etiology in the form of CHILD (congenital hemidysplasia with ichthyosiform nevus and limb defects) syndrome, type 2 segmental Cowden disease, and fibroblast growth factor receptor 3 epidermal nevus syndrome (García-Hafner-Happle syndrome), whereas Proteus syndrome is still of unknown origin. From this overview, it is clear that a specific type of these disorders cannot be classified by the name "epidermal nevus syndrome" nor by the terms "organoid nevus syndrome" or "keratinocytic nevus syndrome."

LEARNING OBJECTIVES

After completing this learning activity, participants should be able to distinguish nine different epidermal nevus syndromes by their characteristic features, understand the practical significance of avoiding terms like "epidermal nevus syndrome" or "keratinocytic nevus syndrome" to define any specific entity within this group of disorders, and differentiate between nonhereditary traits and those bearing a genetic risk because of either Mendelian or non-Mendelian inheritance.

Naevus comedonicus: a spectrum of body involvement

Naevus comedonicus (NC) is a rare developmental anomaly, with < 200 cases reported in the literature. It usually occurs on the face, neck or chest, appearing as groups of closely arranged dilated follicular openings with keratin plugs. Several associations have been made in the literature. We review the current literature, emphasizing the clinical features, associated conditions and therapeutic options.