SCN9A neuropathic pain syndromes (SCN9A-NPS) comprise SCN9A erythromelalgia (EM), SCN9A paroxysmal extreme pain disorder (PEPD), and SCN9A small fiber neuropathy (SFN). SCN9A-EM is characterized by recurrent episodes of bilateral intense, burning pain, and redness, warmth, and occasionally swelling. While the feet are more commonly affected than the hands, in severely affected individuals the legs, arms, face, and/or ears may be involved. SCN9A-PEPD is characterized by neonatal or infantile onset of autonomic manifestations that can include skin flushing, harlequin (patchy or asymmetric) color change, tonic non-epileptic attacks (stiffening), and syncope with bradycardia. Later manifestations are episodes of excruciating deep burning rectal, ocular, or submandibular pain accompanied by flushing (erythematous skin changes). SCN9A-SFN is characterized by adult-onset neuropathic pain in a stocking and glove distribution, often with a burning quality; autonomic manifestations such as dry eyes, mouth, orthostatic dizziness, palpitations, bowel or bladder disturbances; and preservation of large nerve fiber functions (normal strength, tendon reflexes, and vibration sense).

The osteopetroses are a heterogeneous group of genetic disorders characterized by increased bone density due to impaired bone resorption by osteoclasts. Autosomal dominant osteopetrosis-1 (OPTA1) is characterized by generalized osteosclerosis most pronounced in the cranial vault. Patients are often asymptomatic, but some suffer from pain and hearing loss. It appears to be the only type of osteopetrosis not associated with an increased fracture rate (summary by Van Hul et al., 2002). Genetic Heterogeneity of Autosomal Dominant Osteopetrosis Autosomal dominant osteopetrosis-2 (OPTA2; 166600) is caused by mutation in the CLCN7 gene (602727) on chromosome 16p13. Autosomal dominant osteopetrosis-3 (OPTA3; 618107) is caused by mutation in the PLEKHM1 gene (611466) on chromosome 17q21.