ITSN1 and Parkinson disease: ITSN1 haploinsufficiency has also recently been implicated in moderate forms of ASD.17 Other studies have highlighted a convergence between ASD and PD, with epidemiologic data suggesting that people with ASD are three times more likely to develop parkinsonism.41 Synaptic transmission dysfunction is emerging as a convergent mechanism between neurodevelopmental and neurodegenerative disease.42,43 Interestingly, the association between ITSN1 and ASD was driven in part by rare PTVs that probands inherited from unaffected parents.