CD27 and X-linked retinal dysplasia: In summary, we found somatic diversification in the CD38int compartment and subpar SHM and CSR in the CD27+ compartment of the patients with pRD; hence, these findings provide additional evidence for early widespread and dysregulated B cell activation in pRD, with predisposition to impaired humoral effector function, consistent with our previous findings of decreased fraction and number of SM B cells.