CLN5 and pulmonary arterial hypertension: Heterozygous germline mutations in BMPRII, such as those observed in patients with familial PAH, contribute to the failure of the receptor to traffic routinely from the ER to Golgi and reach the cell surface; the intracellular withholding, lack of access to the extracellular ligand and endocytic internalization led to altered receptor signaling in response to BMPs (Sobolewski et al., 2008; Morrell, 2010).