Mosaic abnormalities of the skin: review and guidelines from the European Reference Network for rare skin diseases.

BACKGROUND: Cutaneous mosaicism is an area of dermatology in which there has been an explosion of knowledge within the current decade. This has led to fundamental changes in the understanding of the conditions in this field, and to an ongoing paradigm shift in the approach to management of mosaic skin disorders. OBJECTIVES: To lay out the general principles of mosaicism as they are currently understood, summarize the known cutaneous mosaic abnormalities of the skin with associated phenotypic and genotypic information, review the latest trials on targeted therapies and propose guidelines for the general approach to a patient with suspected mosaicism. METHODS: This was a consensus expert review as part of the European Reference Network project (ERN-Skin). CONCLUSIONS: This study provides clinicians with a practical approach to the patient with suspected mosaicism, redefines mosaicism for the modern genetic era, and proposes a new classification system based on genetic mechanism. What's already known about this topic? Cutaneous mosaicism is a complex field of dermatology that encompasses most birthmarks, and many rare syndromes. Some cutaneous patterns are known to be seen in mosaicism. Very few treatment options are available for most mosaic abnormalities of the skin. Recent high-sensitivity genetic techniques have led to an explosion of knowledge about genotype and phenotype in the literature. What does this study add? Expert consensus from the European Reference Network project. Review of knowledge of confirmed mosaic abnormalities of the skin, including cutaneous phenotype, extracutaneous associated features and genotype. Proposed new classification of mosaic abnormalities of the skin by genetic mechanism and therefore inheritance potential. Practical tips on correct sample collection and genetic investigation. Review of trials of targeted therapies. Guidelines for a practical clinical approach to the patient with suspected mosaicism.

Final congenital melanocytic naevi colour is determined by normal skin colour and unaltered by superficial removal techniques: a longitudinal study.

BACKGROUND: Spontaneous lightening of congenital melanocytic naevi (CMN) has not been studied systematically. Final colour is considered an important outcome after superficial removal techniques such as curettage, dermabrasion or laser ablation, and is often compared with colour at birth. OBJECTIVES: To quantify the natural history of CMN lightening over time, and explore phenotypic and genotypic predictors of colour change. METHODS: A longitudinal cohort study was undertaken of 110 patients with CMN (mean follow-up 5·3 years). Accurate colour-space measurements were taken from professional serial photographs of CMN and normal skin. Changes in colour over time were modelled using multiple logistic regression, against phenotypic and genotypic variables. RESULTS: Lightening of CMN was significantly associated with lighter normal skin colour (P < 0·001) and with MC1R variant alleles (red/blonde hair gene) (P < 0·001), but not with CMN colour in the first 3 months of life, NRAS genotype or projected adult size of CMN. Importantly, the final colours of adjacent treated and untreated areas of CMN were indistinguishable. CONCLUSIONS: Final CMN colour in childhood is related to the genetically determined skin colour of the individual, is unrelated to the colour of CMN at birth, and is unaffected by superficial removal. What's already known about this topic? Final colour of congenital melanocytic naevi (CMN) is considered an important outcome after superficial removal techniques such as curettage, dermabrasion or laser ablation, and is often compared with colour at birth. The phenomenon of spontaneous lightening in CMN, in which naevi lighten gradually and sometimes dramatically during childhood, has been described but not systematically studied. What does this study add? Final CMN colour in childhood is significantly associated with the individual's normal skin colour, and with MC1R genotype, and is therefore genetically determined. Final CMN colour is not predictable from CMN colour in the first 3 months of life. Superficial removal techniques do not alter the final colour of CMN.

Does the gene matter? Genotype-phenotype and genotype-outcome associations in congenital melanocytic naevi.

BACKGROUND: Genotype-phenotype studies can identify subgroups of patients with specific clinical features or differing outcomes, which can help shape management. OBJECTIVES: To characterize the frequency of different causative genotypes in congenital melanocytic naevi (CMN), and to investigate genotype-phenotype and genotype-outcome associations. METHODS: We conducted a large cohort study in which we undertook MC1R genotyping from blood, and high-sensitivity genotyping of NRAS and BRAF hotspots in 156 naevus biopsies from 134 patients with CMN [male 40%; multiple CMN 76%; projected adult size (PAS) > 20 cm, 59%]. RESULTS: Mosaic NRAS mutations were detected in 68%, mutually exclusive with BRAF mutations in 7%, with double wild-type in 25%. Two separate naevi were sequenced in five of seven patients with BRAF mutations, confirming clonality. Five of seven patients with BRAF mutations had a dramatic multinodular phenotype, with characteristic histology distinct from classical proliferative nodules. NRAS mutation was the commonest in all sizes of CMN, but was particularly common in naevi with PAS > 60 cm, implying more tolerance to that mutation early in embryogenesis. Facial features were less common in double wild-type patients. Importantly, the incidence of congenital neurological disease, and apparently of melanoma, was not altered by genotype; no cases of melanoma were seen in BRAF-mutant multiple CMN, however, this genotype is rare. CONCLUSIONS: CMN of all sizes are most commonly caused by mutations in NRAS. BRAF is confirmed as a much rarer cause of multiple CMN, and appears to be commonly associated with a multinodular phenotype. Genotype in this cohort was not associated with differences in incidence of neurological disease in childhood. However, genotyping should be undertaken in suspected melanoma, for guidance of treatment. What's already known about this topic? Multiple congenital melanocytic naevi (CMN) have been shown to be caused by NRAS mosaic mutations in 70-80% of cases, by BRAF mosaicism in one case report and by inference in some previous cases. There has been debate about genotypic association with different sizes of CMN, and no data on genotype-outcome. What does this study add? NRAS mosaicism was found in 68%, BRAF in 7% and double wild-type in 25% of cases of CMN. NRAS was the commonest mutation in all sizes of CMN, but was nearly universal in projected adult size > 60 cm. BRAF is often associated with a distinct multinodular clinical/histological phenotype. Adverse outcomes did not differ between genotypes on current numbers.

Melanoma in congenital melanocytic naevi.

Congenital melanocytic naevi (CMN) are a known risk factor for melanoma, with the greatest risk currently thought to be in childhood. There has been controversy over the years about the incidence of melanoma, and therefore over the clinical management of CMN, due partly to the difficulties of histological diagnosis and partly to publishing bias towards cases of malignancy. Large cohort studies have demonstrated that melanoma risk in childhood is related to the severity of the congenital phenotype. New understanding of the genetics of CMN offers the possibility of improvement in diagnosis of melanoma, identification of those at highest risk, and new treatment options. We review the world literature and our centre's experience over the last 25 years, including the molecular characteristics of melanoma in these patients and new melanoma incidence and outcome data from our prospective cohort. Management strategies are proposed for presentation of suspected melanoma of the skin and the central nervous system in patients with CMN, including use of oral mitogen-activated protein kinase kinase inhibitors in NRAS-mutated tumours.

Growth and hormone profiling in children with congenital melanocytic naevi.

BACKGROUND: Multiple congenital melanocytic naevi (CMN) is a rare mosaic RASopathy, caused by postzygotic activating mutations in NRAS. Growth and hormonal disturbances are described in germline RASopathies, but growth and hormone status have not previously been investigated in individuals with CMN. OBJECTIVES: To explore premature thelarche, undescended testes, and a clinically abnormal fat distribution with CMN through prospective endocrinological assessment of a cohort of subjects with CMN, and a retrospective review of longitudinal growth of a larger group of patients with CMN from outpatient clinics (which included all subjects in the endocrinological assessment group). PATIENTS AND METHODS: Longitudinal growth in a cohort of 202 patients with single or multiple CMN was compared with the U.K. National Child Measurement Programme 2010. Forty-seven children had hormonal profiling including measurement of circulating luteinizing hormone, follicle-stimulating hormone, thyroid stimulating hormone, adrenocorticotrophic hormone, growth hormone, prolactin, pro-opiomelanocortin, estradiol, testosterone, cortisol, thyroxine, insulin-like growth factor-1 and leptin; 10 had oral glucose tolerance testing 25 had dual-energy X-ray absorptiometry scans for body composition. RESULTS: Body mass index increased markedly with age (coefficient 0·119, SE 0·016 standard deviation scores per year), at twice the rate of the U.K. population, due to increased adiposity. Three per cent of girls had premature thelarche variant and 6% of boys had persistent undescended testes. Both fat and muscle mass were reduced in areas underlying large naevi, resulting in limb asymmetry and abnormal truncal fat distribution. Anterior pituitary hormone profiling revealed subtle and variable abnormalities. Oral glucose tolerance tests revealed moderate-severe insulin insensitivity in five of 10, and impaired glucose tolerance in one. CONCLUSIONS: Interpersonal variation may reflect the mosaic nature of this disease and patients should be considered individually. Postnatal weight gain is potentially related to the underlying genetic defect; however, environmental reasons cannot be excluded. Naevus-related reduction of fat and muscle mass suggests local hormonal or metabolic effects on development or growth of adjacent tissues, or mosaic involvement of these tissues at the genetic level. Premature thelarche and undescended testes should be looked for, and investigated, as for any child.

Classification of neurological abnormalities in children with congenital melanocytic naevus syndrome identifies magnetic resonance imaging as the best predictor of clinical outcome.

BACKGROUND: The spectrum of central nervous system (CNS) abnormalities described in association with congenital melanocytic naevi (CMN) includes congenital, acquired, melanotic and nonmelanotic pathology. Historically, symptomatic CNS abnormalities were considered to carry a poor prognosis, although studies from large centres have suggested a much wider variation in outcome. OBJECTIVES: To establish whether routine MRI of the CNS is a clinically relevant investigation in children with multiple CMN (more than one at birth), and to subclassify radiological abnormalities. METHODS: Of 376 patients seen between 1991 and 2013, 289 fulfilled our criterion for a single screening CNS MRI, which since 2008 has been more than one CMN at birth, independent of size and site of the largest naevus. Cutaneous phenotyping and radiological variables were combined in a multiple regression model of long-term outcome measures (abnormal neurodevelopment, seizures, requirement for neurosurgery). RESULTS: Twenty-one per cent of children with multiple CMN had an abnormal MRI. Abnormal MRI was the most significant predictor of all outcome measures. Abnormalities were subclassified into group 1 'intraparenchymal melanosis alone' (n = 28) and group 2 'all other pathology' (n = 18). Group 1 was not associated with malignancy or death during the study period, even when symptomatic with seizures or developmental delay, whereas group 2 showed a much more complex picture, requiring individual assessment. CONCLUSIONS: For screening for congenital neurological lesions a single MRI in multiple CMN is a clinically relevant strategy. Any child with a stepwise change in neurological/developmental symptoms or signs should have an MRI with contrast of the brain and spine to look for new CNS melanoma.

New vascular classification of port-wine stains: improving prediction of Sturge-Weber risk.

BACKGROUND: Facial port-wine stains (PWSs) are usually isolated findings; however, when associated with cerebral and ocular vascular malformations they form part of the classical triad of Sturge-Weber syndrome (SWS). OBJECTIVES: To evaluate the associations between the phenotype of facial PWS and the diagnosis of SWS in a cohort with a high rate of SWS. METHODS: Records were reviewed of all 192 children with a facial PWS seen in 2011-13. Adverse outcome measures were clinical (seizures, abnormal neurodevelopment, glaucoma) and radiological [abnormal magnetic resonance imaging (MRI)], modelled by multivariate logistic regression. RESULTS: The best predictor of adverse outcomes was a PWS involving any part of the forehead, delineated at its inferior border by a line joining the outer canthus of the eye to the top of the ear, and including the upper eyelid. This involves all three divisions of the trigeminal nerve, but corresponds well to the embryonic vascular development of the face. Bilateral distribution was not an independently significant phenotypic feature. Abnormal MRI was a better predictor of all clinical adverse outcome measures than PWS distribution; however, for practical reasons guidelines based on clinical phenotype are proposed. CONCLUSIONS: Facial PWS distribution appears to follow the embryonic vasculature of the face, rather than the trigeminal nerve. We propose that children with a PWS on any part of the 'forehead' should have an urgent ophthalmology review and a brain MRI. A prospective study has been established to test the validity of these guidelines.

Immunohistochemical and ultrastructural features of congenital melanocytic naevus cells support a stem-cell phenotype.

BACKGROUND: Multiple congenital melanocytic naevi (CMN) in one individual are caused by somatic mosaicism for NRAS mutations; however, the lineage of the mutated cells remains uncertain. OBJECTIVES: To test the hypothesis that CMN may be derived from cutaneous stem cells. METHODS: Sixty-six CMN samples from 44 patients were stained for immunohistochemical (IHC) markers of melanocytic differentiation (TYR, TRP1, TRP2, LEF1, MITF, cKit), pluripotency (nestin, fascin, CD133, CD20, CD34), monocyte/macrophage lineage (CD68, CD163, CD14), proliferation (Ki67) and MTOR/Wnt-signalling pathway activation (pS6, ß-catenin). Semiquantitative scoring compared samples with naevus cell nesting (group 1) with those with only diffuse dermal infiltration (group 2). Transmission electron microscopy (TEM) was performed on 10 samples. RESULTS: A normal melanocyte population was seen overlying many dermal CMN. Group 1 samples were significantly more likely to express melanocytic differentiation markers than group 2, and expression decreased significantly with depth. Expression of these markers was correlated with each other, and with nestin and fascin. CD20 staining was positive in a substantial proportion and was stronger superficially. Expression of ß-catenin and pS6 was almost universal. Some samples expressed monocyte/macrophage markers. TEM revealed variable naevus cell morphology, striking macromelanosomes, double cilia and microvilli. CONCLUSIONS: Congenital melanocytic naevi development frequently coexists with normal overlying melanocyte development, leading us to hypothesize that in these cases CMN are likely to develop from a cell present in the skin independent of, or remaining after, normal melanocytic migration. IHC and TEM findings are compatible with CMN cells being of cutaneous stem-cell origin, capable of some degree of melanocytic differentiation superficially.

Great Ormond Street Hospital for Children Registry for congenital melanocytic naevi: prospective study 1988-2007. Part 1-epidemiology, phenotype and outcomes.

BACKGROUND: The aetiology of congenital melanocytic naevi (CMNs) is unknown. OBJECTIVES: To identify potential aetiological factors in families of children with CMNs, and to relate these to long-term outcome measures. METHODS: Three hundred and forty-nine CMN families completed questionnaires about pregnancy and parental factors, and yearly questionnaires on the health of their child and details of the CMN. Seventy-nine control families completed one set of questionnaires, excluding CMN details. RESULTS: The mean prospective follow-up of 301 CMN families was 9.2 years, median 8.9 years, total 2679 years. Forty per cent of patients had CMNs > 20 cm projected adult size (PAS) or multiple CMNs. Twenty per cent of patients had abnormal neurodevelopment and although this was positively associated with PAS it was seen across all size categories. The rate of malignant melanoma was 1.4%. This was strongly associated with PAS with all five cases in patients with CMNs > 60 cm PAS/multiple CMNs (rate in that group 14%). Twenty-five per cent of CMN patients had a positive family history of a CMN in a second-degree relative (FHCMN). This group had a significantly different gender ratio, suggesting a different underlying mutation. Maternal FHCMN was negatively associated with PAS and satellites at birth, and maternal freckling was negatively associated with PAS. Other factors found to be significantly increased in CMN families compared with controls were maternal smoking and ill health during pregnancy. Maternal smoking was positively associated with PAS. CONCLUSIONS: This study relies on data from families after they have had a child with a CMN, and therefore may be subject to recall bias. Despite this, it contributes significantly to the knowledge of epidemiology of CMNs, and provides some important clues to the genetic basis of the condition.