Genetische Grundlagen seborrhoischer Keratosen und epidermaler Nävi

Mosaic RASopathies concept: different skin lesions, same systemic manifestations?

BACKGROUND

Cutaneous epidermal nevi are genotypically diverse mosaic disorders. Pathogenic hotspot variants in HRAS, KRAS, and less frequently, NRAS and BRAF may cause isolated keratinocytic epidermal nevi and sebaceous nevi or several different syndromes when associated with extracutaneous anomalies. Therefore, some authors suggest the concept of mosaic RASopathies to group these different disorders.

METHODS

In this paper, we describe three new cases of syndromic epidermal nevi caused by mosaic HRAS variants: one associating an extensive keratinocytic epidermal nevus with hypomastia, another with extensive mucosal involvement and a third combining a small sebaceous nevus with seizures and intellectual deficiency. Moreover, we performed extensive literature of all cases of syndromic epidermal nevi and related disorders with confirmed pathogenic postzygotic variants in HRAS, KRAS, NRAS or BRAF.

RESULTS

Most patients presented with bone, ophthalmological or neurological anomalies. Rhabdomyosarcoma, urothelial cell carcinoma and pubertas praecox are also repeatedly reported. KRAS pathogenic variants are involved in 50% of the cases, especially in sebaceous nevi, oculoectodermal syndrome and encephalocraniocutaneous lipomatosis. They are frequently associated with eye and brain anomalies. Pathogenic variants in HRAS are rather present in syndromic keratinocytic epidermal nevi and phacomatosis pigmentokeratotica.

CONCLUSION

This review delineates genotype/phenotype correlations of syndromic epidermal nevi with somatic RAS and BRAF pathogenic variants and may help improve their follow-up.

Seborrheic keratosis

Seborrheic keratosis (SK) is the most common benign epidermal tumor in clinical dermatological practice. This review summarizes current knowledge about the clinical and histological appearance, epidemiology, pathogenesis, and treatment of SK. There are different subtypes of SK based on clinical presentation and histologic findings. Several factors, including age, genetic predisposition, and possibly also exposure to ultraviolet radiation, are thought to contribute to the development of SK. The lesions can occur on all areas of the body except for the palms and soles, but the most common sites are the face and upper trunk. The diagnosis is usually made clinically, and in some cases by dermatoscopy or histology. Many patients prefer to have the lesions removed for cosmetic reasons although there is no medical indication. Treatment options include surgical therapy, laser therapy, electrocautery, cryotherapy, and topical drug therapy, which is currently in development. Treatment should be individualized depending on the clinical picture and patient preference.

Two cases of seborrheic keratosis of the external ear canal: involvement of PIK3CA and FGFR3 genes

BACKGROUND

Seborrheic keratosis (SK) of the outer ear canal is rarely described in literature. Etiological risk factors involved in SK such as exposure to human papillomavirus (HPV) and ultraviolet (UV) light are established but must still be confirmed. In recent years, new insights into the pathogenesis of SKs occurred in the area of molecular pathogenesis. Fibroblast growth factor receptor 3 (FGFR3) gene and p110α subunit of phosphoinositide 3-kinase (PIK3CA) oncogene mutations are known to be involved.

METHODS

We describe two cases of SK of the outer ear canal. We conducted a review of literature and examined the role of etiological risk factors involved in our cases. The lesions were primarily treated with surgical resection. Postoperatively, in both patients, the lesions recurred after a considerably long disease-free interval. We tested both FGFR3 and PIK3CA genes for mutations, in the primary and recurrent lesions.

RESULTS

We did not find any mutations in both genes in all samples.

CONCLUSION

Additional research is needed to further establish possible etiological risk factors and to clarify the involvement of PIK3CA and FGFR3 genes in the pathogenesis of seborrheic keratosis of the outer ear canal. These cases underscore the need for meticulous diagnosis, treatment, and sufficient long-term follow-up.