Model of molecular pathogenesis of WIPF1 haploinsufficiency. A schematic diagram for the proposed model of molecular pathogenesis of WIPF1 haploinsufficiency. WIP is the protein product of WIPF1 and is required to bind and stabilize WAS protein (WAS-P) at the N terminus. (A) In individuals with 2 wild-type copies of WIPF1, there are normal levels of WAS messenger RNA (mRNA) and WAS-P. (B) In heterozygotes for WIPF1 LoF, there is less WAS-P despite normal WAS mRNA levels. (C) Similarly, for biallelic WIPF1 LoF, there is barely detectable WAS-P in the setting of normal WAS mRNA. Individuals with biallelic WIPF1 mutations have WAS type 2.