according to Beth Drolet, MD.
“We now know that 75%-80% of vascular malformations have gene mutations that make the cells either live longer, grow faster, or make them bigger in size,” Dr. Drolet, professor and chair of dermatology at the University of Wisconsin–Madison, said during the Society for Pediatric Dermatology pre-AAD meeting. “The basic binary premise of the current ISSVA [International Society for the Study of Vascular Anomalies] classification dividing vascular anomalies into tumors and malformations is wrong; the biology is not that straightforward. It may be helpful to differentiate between an infantile hemangioma and a capillary malformation during infancy as the hemangioma will grow in the next month, but we now know that patients with capillary malformations also have significant overgrowth of their tissue. We’ve all seen that; it just takes years, not months for us to notice it.”
The change in thinking about the root causes of vascular anomalies, she noted, stems from scientific advances in the understanding of embryonic mosaicism, DNA variation that happens after the zygote is formed, but before birth. “We know that each cell in a zygote will undergo 40 cell divisions before a baby is born,” she said. “Those cell divisions are not as neat as we thought they were. That cell and DNA duplication is actually quite messy, so there are mutations that happen purely because of embryonic cell division.”
Everyone is born with 120 somatic mutations per cell, she continued, “so we have multiple genomes in one human. Not all of those mutations are going to cause disease. Not all of those are going to be functional. About 10% of those mutations will actually be in a coding region of the gene and have the potential to change the function of the protein. If it changes the function of the protein so that the cell can’t survive, that cell dies off, but it gives the cell an advantage. It grows a little bit faster, let’s say. That cell survives, divides, producing a line of cells that can cause disease.”
In 2011, Dr. Drolet and colleagues from the Hemangioma Investigator Group and the Pediatric Dermatology Research Alliance (PeDRA) launched a multisite collaborative group to investigate the role of mosaic genetics in patients with vascular anomalies and discrepancy of growth. To date, 365 patients are enrolled, and the researchers have sequenced 97 of 165 affected tissue samples collected. “What’s nice about the registry is that we enrolled a wide spectrum of diseases: very mild diseases that might be treated by dermatologists to complex, syndromic diseases that might end up in an interdisciplinary vascular anomalies clinic,” she said.
For gene sequencing, the researchers drew from solid tumor biology and used next-generation sequencing with semi-target hybrid capture, “so we’re only looking at a subset of genes,” she said. “Right now, the chip we’re using has 180 cancer-related genes. It sequences the entire exome of the gene with a high depth of coverage, usually over 1,000 X. We use a specific pipeline that can detect very low allele frequency mutation: down to 1%, and robust criteria to determine variant pathogenicity.”
In 75% of tissue samples so far, the researchers have found a gene mutation in one of 13 genes: AKT1, AKT3, BRAF, GNA11, GNAQ, KRAS, MAP2K1, NRAS, PIK3CA, PIK3R1, PTPN11, RASA1, and TEK. According to Dr. Drolet, the common thread in these 13 genes is that they are implicated in cancer and have direct control over the cell cycle. “They’re intracellular proteins that control the cell cycle,” she explained. “These are proteins that are in the cell but interact with transmembrane proteins that receive extracellular messengers of cell growth”.
Understanding and recognizing genetic conditions is complicated, she said, because it involves determining which gene is altered, where in the DNA the gene is altered, how the gene variation will influence the function of the protein, and what tissue expresses that gene. “Then you get your phenotype,” Dr. Drolet said. “If you add mosaicism onto that, you have several additional variables. You need to know: When in embryogenesis did the mutation occur? What region of the body is affected? What cell lineage is affected? That predicts what phenotype you’re going to have.”
While molecular classification efforts continue to be refined, Dr. Drolet incorporates genotyping at every opportunity, like when she counsels parents of a baby born with a vascular stain on its face. “What can we tell them about what else might be wrong? What can we tell them about how this will change over time? What can we tell them about how we can treat it? I think genotyping absolutely helps to clarify that for me,” she said. “I can’t use that alone, but it gives me another piece of evidence to help do a better job in predicting when I need to screen, what I need to screen for, and what might happen in the future. If you combine your genotype with your clinical exam, I really do believe we can start to offer some prognostication for our families, to say, ‘this is the degree of overgrowth we may see over time; these are the complications I predict that you might have.’ ”
Even the vascular stain can give you a clue. “If it’s light and lacey, you probably don’t have a lot of cell cycle activation,” Dr. Drolet said. “If it’s dark and there’s blebs and you’ve got some bleeding at a young age, you’ve got a highly activated mutation, and there’s everything in between.”
Dr. Drolet disclosed that she is a consultant for Venthera and Novartis and is a board member for the Isthmus Project. She also holds intellectual property rights in and is a patent holder for Peds Derm Development Group. Dr. Drolet has also received funding from the Spirit Foundation, Kayleigh’s Crew Endowment, the SPD, PeDRA, and the National Institutes of Health.