Giant café-au-lait macule in neurofibromatosis 1: a type 2 segmental manifestation of neurofibromatosis 1?

Superimposed Mosaicism in the Form of Extremely Extended Segmental Plexiform Neurofibroma Caused by a Novel Pathogenic Variant in the NF1 Gene

Plexiform neurofibromas occurring in approximately 20-50% of all neurofibromatosis type-1 (NF1) cases are histologically benign tumors, but they can be fatal due to compression of vital structures or transformation to malignant sarcomas or malignant peripheral nerve sheath tumors. All sizeable plexiform neurofibromas are thought to result from an early second mutation giving rise to a loss of heterozygosity of the NF1 gene. In this unusual case, a 12-year-old girl presented with a rapidly growing, extremely extensive plexiform neurofibroma with segmental distribution over the entire right arm, extending to the right chest wall and mediastinum, superimposed on classic cutaneous lesions of NF1. After several surgical interventions, the patient was efficiently treated with an oral selective MEK inhibitor, selumetinib, which resulted in a rapid reduction of the tumor volume. Molecular analysis of the NF1 gene revealed a c.2326-2 A>G splice-site mutation in the clinically unaffected skin, peripheral blood sample, and plexiform neurofibroma, which explains the general clinical symptoms. Furthermore, a novel likely pathogenic variant, c.4933dupC (p.Leu1645Profs*7), has been identified exclusively in the girl's plexiform neurofibromas. This second-hit mutation can explain the extremely extensive segmental involvement.

Longitudinal phenotype development in a minipig model of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a rare, autosomal dominant disease with variable clinical presentations. Large animal models are useful to help dissect molecular mechanisms, determine relevant biomarkers, and develop effective therapeutics. Here, we studied a NF1 minipig model (NF1+/ex42del) for the first 12 months of life to evaluate phenotype development, track disease progression, and provide a comparison to human subjects. Through systematic evaluation, we have shown that compared to littermate controls, the NF1 model develops phenotypic characteristics of human NF1: [1] café-au-lait macules, [2] axillary/inguinal freckling, [3] shortened stature, [4] tibial bone curvature, and [5] neurofibroma. At 4 months, full body computed tomography imaging detected significantly smaller long bones in NF1+/ex42del minipigs compared to controls, indicative of shorter stature. We found quantitative evidence of tibial bowing in a subpopulation of NF1 minipigs. By 8 months, an NF1+/ex42del boar developed a large diffuse shoulder neurofibroma, visualized on magnetic resonance imaging, which subsequently grew in size and depth as the animal aged up to 20 months. The NF1+/ex42del minipig model progressively demonstrates signature attributes that parallel clinical manifestations seen in humans and provides a viable tool for future translational NF1 research.

Adult-onset kaposiform hemangioendothelioma with neurofibromatosis type 1: A case report and literature review

Kaposiform hemangioendothelioma (KHE) is a very rare, locally aggressive vascular neoplasm. It occurs mostly in children and is rarely observed in adults. It typically originates on the skin, later affecting the deep soft tissue of the extremities, head or neck, and retroperitoneum by infiltrative growth. It is locally aggressive, does not regress spontaneously, and tends to metastasize locally as well as to the regional lymph nodes. In this article, we report a case of adult-onset KHE with neurofibromatosis type 1. The patient presented to our department with a 2-month history of a painful ulceration in her left popliteal area. Since KHE had not previously been reported in patients with neurofibromatosis, the diagnosis was difficult due to the similarity of the skin manifestation to neurofibromatosis-associated lesions. We share our experience of diagnosing and treating this rare case of adult-onset KHE.

The concept of type 2 segmental mosaicism, expanding from dermatology to general medicine

In autosomal dominant skin disorders, the well-known type 1 segmental mosaicism reflects heterozygosity for a postzygotic new mutation. By contrast, type 2 segmental mosaicism originates in a heterozygous embryo from an early postzygotic mutational event giving rise to loss of the corresponding wild-type allele, which results in a pronounced segmental involvement being superimposed on the ordinary, non-segmental phenotype. Today, this concept has been proven by molecular analysis in many cutaneous traits. The purpose of this review was to seek publications of cases suggesting an extracutaneous manifestation of type 2 segmental mosaicism. Case reports documenting a pronounced extracutaneous segmental involvement were collected from the literature available in PubMed and from personal communications to the author. Pertinent cases are compared to the description of cutaneous segmental mosaicism of type 1 or type 2 as reported in a given trait. In total, reports suggesting extracutaneous type 2 segmental mosaicism were found in 14 different autosomal dominant skin disorders. In this way, clinical evidence is accumulated that extracutaneous type 2 segmental mosaicism does likewise occur in many autosomal dominant skin disorders. So far, however, molecular proof of this particular form of mosaicism is lacking. The present review may stimulate readers to inform colleagues of other specialties on this new concept, in order to initiate further research in this particular field of knowledge that has important implications for diagnosis, treatment and genetic counselling.

Phacomatosis pigmento-pigmentaria: should we add a new type of phacomatosis? Fact and controversies

There are currently five types of recognized phacomatosis pigmentovascularis plus one more, phacomatosis pigmentokeratotica, making six types altogether. Should we stop here and consider the classification as being complete? Or, do we leave room to add more types or, alternatively, lump the ones we have together and shorten the list? We present our reasons for adding one or two new types of phacomatoses to the current classification, in full recognition that it is already complicated and somewhat cumbersome. We consider that the benefits of doing so outweigh any additional strain on the already complicated classification. We expect that this might not sit well with some of our colleagues, but we are prepared to do battle.

A case of linear porokeratosis superimposed on disseminated superficial actinic porokeratosis

We present a female patient with linear porokeratosis of her right arm since childhood. At the age of 67 years she additionally developed disseminated superficial actinic porokeratosis (DSAP) involving both lower legs. This uncommon coexistence of two different types of porokeratosis fulfils the clinical criteria of a type 2 segmental manifestation of an autosomal dominant skin disorder, being superimposed on the ordinary nonsegmental lesions and reflecting loss of heterozygosity that occurred at an early developmental stage. In DSAP molecular evidence of this concept is so far lacking, but such proof has already been provided in several other autosomal dominant skin disorders. Molecular analysis of cases of type 2 segmental involvement may help elucidate the genetic defect causing DSAP.

Cutaneous mosaicism: a molecular and clinical review

Physicians have long been intrigued by the distinct patterns created by epidermal nevi and other mosaic cutaneous disorders. Although many of the molecular mechanisms underlying these disorders remain unrevealed, with the release of the results of the Human Genome Project our knowledge is rapidly increasing. The underlying genetic defects for many of the X-linked and mosaic disorders have recently been identified. Advances in technology, such as the array comparative genomic hybridization, will provide the tools for continued gene discovery and expanded understanding of the pathogenic mechanisms underlying mosaic skin conditions.

Mosaic manifestations of monogenic skin diseases

A genetic mosaic is defined as an organism which is composed of genetically different cell lines which originate from a homogeneous zygote. Etiologically, cutaneous mosaics can be divided into two large categories, epigenetic mosaicism and genomic mosaicism. Genomic mosaics which have two or more genetically different cell populations are not inherited with the exception of para-dominant inheritance pattern. Epigenetic mosaics have a structurally homogeneous cell population but there are functional differences induced by modifying factors in the form of gene-steering retroviral elements that can be inherited. We distinguish five different manifestation patterns of mosaicism, including the Blaschko lines pattern, patchy pattern without midline separation, checkerboard pattern, phylloid pattern and lateralization pattern. All forms of epigenetic mosaicism, including the various patterns of X-inactivation, appear to be caused by the action of retrotransposons. A new concept is functional autosomal mosaicism transmittable through the action of retrotransposons