Genetic Profile of Epidermolysis Bullosa Cases in King Abdulaziz Medical City, Riyadh, Saudi Arabia

The Greater Middle East (GME) has been a central hub of human migration and population admixture. The tradition of consanguinity, variably practiced in the Gulf region, North Africa, and Central Asia 1–3 , has resulted in an elevated burden of recessive disease 4 . Here we generated a whole exome GME variome from 1,111 unrelated subjects. We detected substantial diversity from sub-geographies, continental and subregional admixture, several ancient founder populations with little evidence of bottlenecks. Measured consanguinity was an order-of-magnitude above that of other sampled populations, and included an increased burden of runs of homozygosity (ROH), but no evidence for reduced burden of deleterious variation due to classically theorized ‘genetic purging’. Applying this database to unsolved GME recessive conditions reduced the number of potential disease-causing variants by 4–7-fold. These results reveal the variegated GME genetic architecture and support future human genetic discoveries in Mendelian and population genetics.

Case series have demonstrated that potentially lethal cutaneous squamous cell carcinomas arise in patients with recessive dystrophic epidermolysis bullosa (RDEB), although the magnitude of this risk is undefined. Systematic case finding and data collection were performed throughout the continental United States (1986-2002) by the National EB Registry on 3280 EB patients to determine cumulative and conditional risks for squamous cell carcinoma (SCC), basal cell carcinoma (BCC), and malignant melanoma (MM) within each major EB subtype, as well as the cumulative risk of death from each tumor. Study design was cross-sectional, with a nested randomly sampled longitudinal subcohort (N = 450). SCCs arose primarily in RDEB, especially the Hallopeau-Siemens subtype (RDEB-HS), first beginning in adolescence. Less frequently, SCCs occurred in junctional EB (JEB). Cumulative risks rose steeply in RDEB-HS, from 7.5% by age 20 to 67.8%, 80.2%, and 90.1% by ages 35, 45, and 55, respectively. In Herlitz JEB, the risk was 18.2% by age 25. SCC deaths occurred only in RDEB, with cumulative risks in RDEB-HS of 38.7%, 70.0%, and 78.7% by ages 35, 45, and 55, respectively. MM arose in RDEB-HS, with a cumulative risk of 2.5% by age 12. BCCs arose almost exclusively in the most severe EB simplex subtype (Dowling-Meara) (cumulative risk = 43.6% by age 55). Mutational analyses were performed on only a minority of enrollees in the National EB Registry, preventing evaluation of the possible influence of specific genotypes on the risk of developing or dying from cutaneous SCCs. SCC is the most serious complication of EB within adults, especially those with RDEB-HS. By mid-adulthood, nearly all will have had at least one SCC, and nearly 80% will have died of metastatic SCC despite aggressive surgical resection. When compared with SCCs arising within the normal population, the remarkably high risk of occurrence of and then death from SCCs among RDEB patients suggests likely differences in pathogenesis. Additional studies of EB-derived tumors and SCC cell lines may not only provide new insights into the mechanisms of carcinogenesis but also means whereby these particular tumors may be prevented or more effectively treated.