Mutations of the CD55 gene have been identified by an international group of scientists as the cause of a new autosomal recessively inherited syndrome consisting of early-onset protein-losing enteropathy associated with primary intestinal lymphangiectasia, bowel inflammation and thrombosis.

The researchers studied 11 patients with abdominal pain and diarrhea who presented with early-onset protein-losing enteropathy, edema due to hypoproteinemia, malabsorption, and less frequently, intestinal inflammation, recurrent infections and thrombosis. Whole-exome sequencing identified homozygous mutations in CD55 as the genetic cause of the condition which they termed CHAPLE syndrome. Further functional investigations in patients’ T lymphocytes revealed that the mutations result in a loss of CD55 protein function, leading to increased complement activation causing surface deposition of complement and the generation of soluble C5a.

CD55 is one of multiple factors regulating the complement system, a complex cascade of interacting plasma proteins that forms part of the innate immune system and clears microorganisms and damaged cells from the organism. Mutations in other genes leading to complement hyperactivation have previously been determined as causing monogenic disorders like, for example, paroxysmal nocturnal hemoglobulinuria (PNH) and atypical hemolytic uremic syndrome.

Ozen et al. now report in the New England Journal of Medicine that isolated CD55 deficiency results in early-onset protein-losing enteropathy due to primary intestinal lymphangiectasia and bowel inflammation. Furthermore, their functional studies suggest a potential targeted therapeutic approach, as incubation of patient cells with eculizumab, a complement-inhibitory antibody used in the treatment of PNH and atypical hemolytic uremic syndrome, suppressed C5a production. This is even more interesting as with Kurolap et al. also another group of researchers reported in the same issue of the journal a positive effect of eculizumab in a family with CHAPLE syndrome.