mitogen-activated protein kinasepERK
TO THE EDITOR
Nevus sebaceus is a common congenital skin hamartoma, classically appearing as a yellow-hued plaque on the scalp, face, or neck. It is the hallmark lesion of Schimmelpenning/nevus sebaceus syndrome (OMIM: 163200), a multisystem disorder that includes a spectrum of central nervous system, ocular, skeletal, and cardiovascular defects. Secondary neoplasms arise within nevus sebaceus at a modest but elevated rate (
Moody et al., 2012), prompting disagreement about whether they should be routinely excised (
- Moody M.
- Landau J.
- Goldberg L.
Nevus sebaceous revisited.
Pediatr Dermatol. 2012; 29: 15-23
Shwayder, 2011). Determining the pathogenesis of nevus sebaceus would provide a framework to better understand this lesion and its associated syndrome.
- Shwayder T.
Re: Management of nevus sebaceous and the risk of basal cell carcinoma: an 18-year review. By Rosen et al.: Pediatric Dermatology v26, n6, 676-681, Nov/Dec 2009.
Pediatr Dermatol. 2011; 28 (author reply 82): 82
The appearance of nevus sebaceus along Blaschko’s lines suggests that a mosaic genetic mutation causes the lesion, with more extensive multisystem involvement potentially underlying the syndromic form (
Happle, 1993). Here, we report a case of an individual with nevus sebaceus syndrome. As individuals with this syndrome are uncommon, we sought to identify associated mutations by comparing the exome sequence of the nevus sebaceus from our patient with those of sporadic nevus sebaceus.
- Happle R.
Mosaicism in human skin. Understanding the patterns and mechanisms.
Arch Dermatol. 1993; 129: 1460-1470
Our index patient is a 38-year-old woman who was born with Chiari malformation, myelomeningocele, and resultant paraplegia. Because of hydrocephalus and marked ventricomegaly, she required ventriculo-peritoneal shunt placement. Imaging studies demonstrated rotoscoliosis. She has had cognitive developmental delay and suffered from generalized seizures during childhood. In her early thirties, she experienced a middle right cerebral artery stroke. Despite her condition, she remains high functioning and lives in an assisted care facility. No other family members are affected by similar medical conditions, and no cause has been attributed to her findings.
In the past year, the patient became bothered by growths on her forehead and presented to our clinic. On examination, frontal bossing was observed, as well as a yellow-hued papillomatous plaque on the paramidline forehead that had been present since birth (Figure 1a). Several pedunculated papules were noted within the lesion. No other significant cutaneous findings were appreciated.
As per patient request, the lesion was excised and a portion of the excision specimen was collected with her written informed consent. Our study complied with the Declaration of Helsinki Principles and was approved by the Stanford Institutional Review Board. Histological evaluation confirmed features of nevus sebaceus with no secondary neoplasms (Figure 1b). Accordingly, in light of the extensive neurological and skeletal involvement, a diagnosis of Schimmelpenning/nevus sebaceus syndrome was made. In efforts to determine an underlying genetic mutation, four additional, independent nevus sebaceus samples were collected from elective excisions along with adjacent normal skin controls. The five samples were subjected to exome sequencing and analyzed for mutations using Seqgene (
Deng, 2011) and DNAnexus (http://www.dnanexus.com) as described in the Supplementary Material online.
- Deng X.
SeqGene: a comprehensive software solution for mining exome- and transcriptome- sequencing data.
BMC Bioinformatics. 2011; 12: 267
Analysis of recurrent lesion-specific variants identified an HRAS point mutation (c.37G>C, p.Gly13Arg) in the index case and in two of four isolated nevus sebaceus samples, with a variant allele frequency ranging from 17 to 43%. Sanger sequencing confirmed the HRAS mutation in all five lesional samples and its absence in all matched controls (Figure 2a). Examination of the two HRAS mutation–negative exomes showed low sequence coverage (<20 reads) at the mutation site, which may account for the false-negative calls.
Lesions arising along Blaschko’s lines are hypothesized to stem from a mosaic mutation affecting a specific cell lineage during development. To evaluate whether the candidate mutation fits this criterion, we used laser capture microdissection to isolate DNA from the lesional epidermis and dermis from the index case and one of the sporadic nevus sebaceus samples. In both cases, the mutation was limited to the epidermis, supporting the hypothesis of an acquired mutation affecting ectodermal precursors (Figure 2b). Both alleles were represented in approximately equal intensities, indicating that the mutation is likely heterozygous.
We next performed targeted Sanger sequencing on a validation set of 31 independent nevus sebaceus samples from archived tissues, and identified the HRAS p.Gly13Arg mutation in 24/31 samples and p.Gly12Asp in one sample. The remaining mutation-negative cases were evaluated for KRAS and NRAS hotspot mutations, identifying two samples carrying KRAS p.Gly12Asp mutations. Six validation samples had patient-matched normal skin tissue available, and the corresponding RAS mutations were absent in all six control samples. In total, 32 of 36 samples (89%) demonstrated HRAS or KRAS mutations, confirming a strong correlation between activating RAS mutations and nevus sebaceus (Figure 2c). We suspect that the remaining negative cases may be due to genetic heterogeneity, or due to a low mutant allele frequency secondary to admixture with normal tissue.
RAS promotes cell growth through activation of multiple pathways, a main pathway being the mitogen-activated protein kinase (MAPK) signal-transduction pathway. Activating mutations in this gene family have well-established links to cancer (
Schubbert et al., 2007). Germline activating HRAS mutations cause Costello syndrome, which features predisposition to neoplasia and development of cutaneous papillomas (
- Schubbert S.
- Shannon K.
- Bollag G.
Hyperactive Ras in developmental disorders and cancer.
Nat Rev Cancer. 2007; 7: 295-308
Gripp and Lin, 2012). Taken together, the known biological features of activated RAS genes are consistent with the hamartomatous overgrowth and elevated neoplasia risk observed in nevus sebaceus.
- Gripp K.
- Lin A.
Costello syndrome: a Ras/mitogen activated protein kinase pathway syndrome (rasopathy) resulting from HRAS germline mutations.
Genet Med. 2012; 14: 285-292
To evaluate RAS-MAPK signaling, we performed phosphorylated ERK (pERK) staining on a set of nevi with confirmed HRAS mutations. Immunohistochemistry revealed increased pERK staining in lesional versus normal epidermis, consistent with RAS-MAPK hyperactivation (Figure 2d). In one sample, a squamous cell carcinoma was identified arising from nevus sebaceus, highlighted by elevated p16 staining (
Hodges and Smoller, 2002). The pattern of neoplasia arising from a background of upregulated pERK supports the hypothesis that RAS-MAPK hyperactivation may predispose toward the development of secondary neoplasms in nevus sebaceus.
- Hodges A.
- Smoller B.
Immunohistochemical comparison of P16 expression in actinic keratoses and squamous cell carcinomas of the skin.
Mod Pathol. 2002; 15: 1121-1125
Basal cell carcinomas were once thought to arise commonly from nevus sebaceus, but others have subsequently contended that the majority of these tumors are actually trichoblastomas (
Cribier et al., 2000). Our data provide genetic support for the latter opinion, as most basal cell carcinomas arise from Hedgehog pathway dysregulation and lack RAS mutations (
- Cribier B.
- Scrivener Y.
- Grosshans E.
Tumors arising in nevus sebaceus: a study of 596 cases.
J Am Acad Dermatol. 2000; 42: 263-268
Reifenberger et al., 2005). Our findings also raise the possibility that tumors arising from nevus sebaceus, such as syringocystadenoma papilliferum and trichoblastomas, may be associated with RAS mutations as well.
- Reifenberger J.
- Wolter M.
- Knobbe C.
- et al.
Somatic mutations in the PTCH, SMOH, SUFUH and TP53 genes in sporadic basal cell carcinomas.
Br J Dermatol. 2005; 152: 43-51
Using targeted sequencing and SNaPshot assays,
Groesser et al., 2012and
- Groesser L.
- Herschberger E.
- Ruetten A.
- et al.
Postzygotic HRAS and KRAS mutations cause nevus sebaceous and Schimmelpenning syndrome.
Nat Genet. 2012; 44: 783-787
Hafner et al., 2012have recently profiled oncogenic hotspot mutations in epidermal and sebaceus nevi. Together with the results presented here and by others in this issue (
- Hafner C.
- Toll A.
- Gantner S.
- et al.
Keratinocytic epidermal nevi are associated with mosaic RAS mutations.
J Med Genet. 2012; 49: 249-253
Levinsohn et al., 2012), the cumulative data demonstrate that keratinocytic epidermal nevi and sebaceus nevi are both associated with activating HRAS p.Gly13Arg and KRAS p.Gly12Asp mutations, supporting the belief held by some clinicians that they represent a spectrum of the same entity (
- Levinsohn J.
- Tian L.
- Boyden L.
- et al.
Whole exome sequencing reveals somatic mutations in HRAS and KRAS which cause nevus sebaceus.
J Invest Dermatol. 2012https://doi.org/10.1038/jid.2012.379
Sybert, 2010). We postulate that the phenotypic difference between these nevi may be related to the extent of the mutation, as well as body site–specific embryological patterns and environment. The knowledge of the genetic basis of nevus sebaceus and its associated syndrome represents a further step toward understanding genotype–phenotype correlations arising from genetic mosaicism.
- Sybert V.
Genetic Skin Disorders (Oxford Monographs on Medical Genetics). 2nd ed. Oxford University Press, USA2010: p784
We thank the patients and their families for taking part in this project. We also thank S Aasi, R Khosla, and P Lorenz for their valuable assistance.
Supplementary material is linked to the online version of the paper at http://www.nature.com/jid
- Supplementary Information
- Tumors arising in nevus sebaceus: a study of 596 cases.J Am Acad Dermatol. 2000; 42: 263-268
- SeqGene: a comprehensive software solution for mining exome- and transcriptome- sequencing data.BMC Bioinformatics. 2011; 12: 267
- Costello syndrome: a Ras/mitogen activated protein kinase pathway syndrome (rasopathy) resulting from HRAS germline mutations.Genet Med. 2012; 14: 285-292
- Postzygotic HRAS and KRAS mutations cause nevus sebaceous and Schimmelpenning syndrome.Nat Genet. 2012; 44: 783-787
- Keratinocytic epidermal nevi are associated with mosaic RAS mutations.J Med Genet. 2012; 49: 249-253
- Mosaicism in human skin. Understanding the patterns and mechanisms.Arch Dermatol. 1993; 129: 1460-1470
- Immunohistochemical comparison of P16 expression in actinic keratoses and squamous cell carcinomas of the skin.Mod Pathol. 2002; 15: 1121-1125
- Whole exome sequencing reveals somatic mutations in HRAS and KRAS which cause nevus sebaceus.J Invest Dermatol. 2012https://doi.org/10.1038/jid.2012.379
- Nevus sebaceous revisited.Pediatr Dermatol. 2012; 29: 15-23
- Somatic mutations in the PTCH, SMOH, SUFUH and TP53 genes in sporadic basal cell carcinomas.Br J Dermatol. 2005; 152: 43-51
- Hyperactive Ras in developmental disorders and cancer.Nat Rev Cancer. 2007; 7: 295-308
- Re: Management of nevus sebaceous and the risk of basal cell carcinoma: an 18-year review. By Rosen et al.: Pediatric Dermatology v26, n6, 676-681, Nov/Dec 2009.Pediatr Dermatol. 2011; 28 (author reply 82): 82
- Genetic Skin Disorders (Oxford Monographs on Medical Genetics). 2nd ed. Oxford University Press, USA2010: p784
The authors state no conflict of interest.
© 2013 The Society for Investigative Dermatology, Inc. Published by Elsevier Inc.
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