Hereditary paraganglioma-pheochromocytoma (PGL/PCC) syndromes are characterized by paragangliomas (tumors that arise from neuroendocrine tissues distributed along the paravertebral axis from the base of the skull to the pelvis) and pheochromocytomas (paragangliomas that are confined to the adrenal medulla). Sympathetic paragangliomas cause catecholamine excess; parasympathetic paragangliomas are most often nonsecretory. Extra-adrenal parasympathetic paragangliomas are located predominantly in the skull base and neck (referred to as head and neck PGL [HNPGL]) and sometimes in the upper mediastinum; approximately 95% of such tumors are nonsecretory. In contrast, sympathetic extra-adrenal paragangliomas are generally confined to the lower mediastinum, abdomen, and pelvis, and are typically secretory. Pheochromocytomas, which arise from the adrenal medulla, typically lead to catecholamine excess. Symptoms of PGL/PCC result from either mass effects or catecholamine hypersecretion (e.g., sustained or paroxysmal elevations in blood pressure, headache, episodic profuse sweating, forceful palpitations, pallor, and apprehension or anxiety). The risk for developing metastatic disease is greater for extra-adrenal sympathetic paragangliomas than for pheochromocytomas.

Congenital central hypoventilation syndrome-3 (CCHS3) is an autosomal recessive disorder characterized by slow and shallow breathing due to a deficiency in autonomic control of respiration. Affected individuals present in the neonatal period with respiratory insufficiency and absence of the hypercapnic reflex that stimulates breathing. Patients also have gastrointestinal problems manifest as feeding difficulties and diarrhea or constipation. Other features may include poor heat tolerance and paroxysmal hypertension (Hernandez-Miranda et al., 2018). For a discussion of genetic heterogeneity of CCHS, see CCHS1 (209880).