Those infants had thefollowing features: brain imaging suggestive of congenital infection; braincalcifications and negative results on tests for other main infectiouscauses of primary microcephaly, namely toxoplasmosis, cytomegalovirus,rubella, and HIV; positivity for Zika virus on IgM antibody captureenzyme-linked immunosorbent assay in cerebrospinal fluid. The gene discussed is CD40LG; the disease is toxoplasmosis.