SMAD4 and juvenile polyposis/hereditary hemorrhagic telangiectasia syndrome: The deletion region contains the <i>TCF4</i> and <i>SMAD4</i> genes, whose haploinsufficiency causes the causative genes of Pitt-Hopkins syndrome (PTHS) and juvenile polyposis/hereditary hemorrhagic telangiectasia (JPHT or JPHHT), respectively.