PTPN1 and Aicardi-Goutieres syndrome: The observation of enhanced type I IFN signalling in patient blood and CSF, and of increased levels of CSF neopterin,25,26 suggests that PTP1B haploinsufficiency can be classified as a novel type I interferonopathy.27 Indeed, the paradigm type I interferonopathy Aicardi-Goutières syndrome (AGS) was considered as a possible diagnosis in a number of the cases described here.