Considering the category of autoinflammatory diseases, the percentages of fetal- and perinatal-onset cases are the highest ones among the IEIs here approached: (i) most cases of NOMID/CINCA and DIRA already had manifestations at birth and (ii) approximately a quarter of AGS cases were clearly affected at birth, as well as all the few USP18 deficiency cases so far described, thus revealing that pathological processes already had begun during the gestational period (82, 85). The gene discussed is USP18; the disease is Aicardi-Goutieres syndrome.