We know that SCLS is not hereditary, or else it would be far more common than it is -- an estimated one in one-million inhabitants, none of whom are related, as far as can be determined. However, many conditions have genetic roots or a genetic component which is not necessarily passed on from generation to generation.
I wanted to call everyone's attention to the fact that, during the past couple of years, Dr. Kirk Druey at NIH has been conducting genetic research on SCLS patients, both adults and children, and he has been publishing his preliminary results. His latest article, which appeared last month (October 2018), "Whole Exome Sequencing of Adult and Pediatric Cohorts of the Rare Vascular Disorder Systemic Capillary Leak Syndrome," has been added to the Disorder Resources section of this website.
Asked to provide a nontechnical summary of his findings, Dr. Druey commented as follows: "We sequenced part of the genome (the exons, which encode proteins) of adult and pediatric SCLS patients. Basically, the takeaway is that we were unable to find gene mutations that were shared by most or all of the patients that could account for the disease. However, it is important to note that these preliminary results by no means exclude the possibility that there is a genetic component to SCLS. Therefore, we are continuing to study the possible genetic contribution to SCLS in complementary ways. Stay tuned!"