Kaposiform hemangioendothelioma and tufted angioma - (epi)genetic analysis including genome-wide methylation profiling.

Kaposiform hemangioendothelioma (KHE) is a locally aggressive vascular condition of childhood and is clinicopathologically related to tufted angioma (TA), a benign skin lesion. Due to their rarity molecular data are scarce. We investigated 7 KHE and 3 TA by comprehensive mutational analysis and genome-wide methylation profiling and compared the clustering, also with vascular malformations. Lesions were from 7 females and 3 males. The age range was 2 months to 9 years with a median of 10 months. KHEs arose in the soft tissue of the thigh (n = 2), retroperitoneum (n = 1), thoracal/abdominal (n = 1), supraclavicular (n = 1) and neck (n = 1). One patient presented with multiple lesions without further information. Two patients developed a Kasabach-Merritt phenomenon. TAs originated in the skin of the shoulder (n = 2) and nose/forehead (n = 1). Of the 5 KHEs and 2 TAs investigated by DNA sequencing, one TA showed a hot spot mutation in NRAS, and one KHE a mutation in RAD50. Unsupervised hierarchical clustering analysis indicated a common methylation pattern of KHEs and TAs, which separated from the homogeneous methylation pattern of vascular malformations. In conclusion, methylation profiling provides further evidence for KHEs and TAs potentially forming a spectrum of one entity. Using next generation sequencing, heterogeneous mutations were found in a subset of cases (2/7) without the presence of GNA14 mutations, previously reported in KHE and TA.

Comprehensive molecular and clinicopathological analysis of vascular malformations: A study of 319 cases.

Vascular malformations are part of overgrowth syndromes characterized by somatic mosaic mutations or rarely by germline mutations. Due to their similarities and diversity, clinicopathological classification can be challenging. A comprehensive targeted Next Generation Sequencing screen using Unique Molecular Identifiers with a technical sensitivity of 1% mutant alleles was performed for frequently mutated positions in ≥21 genes on 319 formalin-fixed paraffin-embedded samples. In 132 out of 319 cases pathogenic mosaic mutations were detected affecting genes previously linked to vascular malformations e.g. PIK3CA (n=80), TEK (TIE2) (n=11), AKT1 (n=1), GNAQ (n=7), GNA11 (n=4), IDH1 (n=3), KRAS (n=9), and NRAS (n=1). Six cases harbored a combination of mutations in PIK3CA and in GNA11 (n=2), GNAQ (n=2), or IDH1 (n=2). Aberrations in PTEN and RASA1 with a variant allele frequency approaching 50% suggestive of germline origin were identified in six out of 102 cases tested; four contained a potential second hit at a lower allele frequency. Ninety-one of the total 142 pathogenic mutations were present at a variant allele frequency <10% illustrating the importance of sensitive molecular analysis. Clinicopathological characteristics showed a broad spectrum and overlap when correlated with molecular data. Sensitive screening of recurrently mutated genes in vascular malformations may help to confirm the diagnosis and reveals potential therapeutic options with a significant contribution of PIK3CA/mTOR and RAS-MAPK pathway mutations. The co-existence of two activating pathogenic mutations in parallel pathways illustrates potential treatment challenges and underlines the importance of multigene testing. Detected germline mutations have major clinical impact.

Mutational analysis using Sanger and next generation sequencing in sporadic spindle cell hemangiomas: A study of 19 cases.

Spindle cell hemangioma (SCH) is a distinct vascular soft-tissue lesion characterized by cavernous blood vessels and a spindle cell component mainly occurring in the distal extremities of young adults. The majority of cases harbor heterozygous mutations in IDH1/2 sporadically or rarely in association with Maffucci syndrome. However, based on mosaicism and accordingly a low percentage of lesional cells harboring a mutant allele, detection can be challenging. We tested 19 sporadic SCHs by Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA), conventional next generation sequencing (NGS), and NGS using a single molecule molecular inversion probes (smMIP)-based library preparation to compare their diagnostic value. Out of 10 cases tested by Sanger sequencing and 2 analyzed using MLPA, 4 and 1, respectively, revealed a mutation in IDH1 (p.R132C). The 7 remaining negative cases and additional 6 cases were investigated using smMIP/NGS, showing hot spot mutations in IDH1 (p.R132C) (8 cases) and IDH2 (3 cases; twice p.R172S and once p.R172G, respectively). One case was negative. Owing to insufficient DNA quality and insufficient coverage, 2 cases were excluded. In total, in 16 out of 17 cases successfully tested, an IDH1/2 mutation was found. Given that IDH1/2 mutations were absent in 161 other vascular lesions tested by smMIP/NGS, the mutation can be considered as highly specific for SCH.

Regulatory factors and cell populations involved in skeletal muscle regeneration.

Skeletal muscle regeneration is a complex process, which is not yet completely understood. Satellite cells, the skeletal muscle stem cells, become activated after trauma, proliferate, and migrate to the site of injury. Depending on the severity of the myotrauma, activated satellite cells form new multinucleated myofibers or fuse to damaged myofibers. The specific microenvironment of the satellite cells, the niche, controls their behavior. The niche contains several components that maintain satellite cells quiescence until they are activated. In addition, a great diversity of stimulatory and inhibitory growth factors such as IGF-1 and TGF-beta1 regulate their activity. Donor-derived satellite cells are able to improve muscle regeneration, but their migration through the muscle tissue and across endothelial layers is limited. Less than 1% of their progeny, the myoblasts, survive the first days upon intra-muscular injection. However, a range of other multipotent muscle- and non-muscle-derived stem cells are involved in skeletal muscle regeneration. These stem cells can occupy the satellite cell niche and show great potential for the treatment of skeletal muscle injuries and diseases. The aim of this review is to discuss the niche factors, growth factors, and other stem cells, which are involved in skeletal muscle regeneration. Knowledge about the factors regulating satellite cell activity and skeletal muscle regeneration can be used to improve the treatment of muscle injuries and diseases.

Functional characterisation of a novel class of in-frame insertion variants of KRAS and HRAS.

Mutations in the RAS genes are identified in a variety of clinical settings, ranging from somatic mutations in oncology to germline mutations in developmental disorders, also known as 'RASopathies', and vascular malformations/overgrowth syndromes. Generally single amino acid substitutions are identified, that result in an increase of the GTP bound fraction of the RAS proteins causing constitutive signalling. Here, a series of 7 in-frame insertions and duplications in HRAS (n = 5) and KRAS (n = 2) is presented, resulting in the insertion of 7-10 amino acids residues in the switch II region. These variants were identified in routine diagnostic screening of 299 samples for somatic mutations in vascular malformations/overgrowth syndromes (n = 6) and in germline analyses for RASopathies (n = 1). Biophysical characterization shows the inability of Guanine Nucleotide Exchange Factors to induce GTP loading and reduced intrinsic and GAP-stimulated GTP hydrolysis. As a consequence of these opposing effects, increased RAS signalling is detected in a cellular model system. Therefore these in-frame insertions represent a new class of weakly activating clinically relevant RAS variants.