Sporadic Onset of Erythermalgia: A Gain-of- Function Mutation in Na v 1.7 Chongyang Han, BS, 1 Anthony M. Rush, PhD, 2–4 Sulayman D. Dib-Hajj, PhD, 2–4 Song Li, MD, PhD, 5 Zhe Xu, MD, 6 Yun Wang, MD, PhD, 5 Lynda Tyrrell, MS, 2–4 Xiaoliang Wang, PhD, 1 Yong Yang, MD, PhD, 5 and Stephen G. Waxman, MD, PhD 2–4 Objective: Inherited erythermalgia (erythromelalgia) is an autosomal dominant disorder in which patients experience severe burning pain in the extremities, in response to mild thermal stimuli and exercise. Although mutations in sodium channel Na v 1.7 have been shown to underlie erythermalgia in several multigeneration families with the disease that have been investigated to date, the molecular basis of erythermalgia in sporadic cases is enigmatic. We investigated the role of Na v 1.7 in a sporadic case of erythermalgia in a Chinese family. Methods: Genomic DNA from patients and their asymp- tomatic family members were sequenced to identify mutations in Na v 1.7. Whole-cell patch clamp analysis was used to characterize biophysical properties of wild-type and mutant Na v 1.7 channels in mammalian cells. Results: A single amino acid substitution in the DIIS4-S5 linker of Na v 1.7 was present in two children whose parents were asymptomatic. The asymptomatic father was genetically mosaic for the mutation. This mutation produces a hyperpolarizing shift in channel activation and an increase in amplitude of the response to slow, small depolarizations. Interpretation: Founder mutations in Na v 1.7, which can confer hyperexcitability on peripheral sensory neurons, can underlie sporadic erythermalgia. Ann Neurol 2006;59:553–558 Inherited erythermalgia (also called erythromelalgia) is a familial painful neuropathy characterized by burning pain and redness of the skin of the extremities in re- sponse to warm stimuli or moderate exercise. 1 The pat- tern of inheritance is autosomal dominant. 2–6 Re- cently, we described mutations in SCN9A, the gene for the Na v 1.7 sodium channel, in two families with er- ythermalgia 4 and their effects on biophysical properties of this channel. 7 Additional families were subsequently reported with mutations of SCN9A. 5,6 Na v 1.7 channels are preferentially expressed in noci- ceptive dorsal root ganglia neurons and sympathetic ganglion neurons 8 –10 and are characterized by slow closed-state inactivation which allows them to amplify small depolarizations such as generator potentials close to resting potential by producing “threshold cur- rents.” 11 Na v 1.7 has recently been shown to play an important role in inflammatory pain. 12,13 Here, we now describe a new mutation in Na v 1.7 in a family with no prior history of erythermalgia, that is, with sporadic onset of the disease. Patients and Methods Patients The proband (Fig 1) was a 15-year-old male who was ad- mitted to the Peking University First Hospital in July 2003. Family consent was obtained according to the institutional review board protocol and blood samples then were with- drawn and analyzed for mutations in SCN9A. Exon Screening Genomic DNA was extracted from blood samples of all fam- ily members. Polymerase chain reaction amplification of the 26 exons of SCN9A was performed, and the amplicons were purified and sequenced as previously described. 4 Genomic se- quences were compared with reference Na v 1.7 cDNA 14 to identify sequence variation. A mutation in exon 15 (L858F) was identified that destroys the recognition site for the re- striction enzyme BstPI in this amplicon. Voltage-Clamp Analysis The L858F mutation was introduced into hNa v 1.7 R which carries a TTX-R version of human Na v 1.7 cDNA 15 using QuickChange XL site-directed mutagenesis (Stratagene, La From the 1 Institute of Materia Medica, Chinese Academy of Med- ical Sciences and Peking Union Medical College, Beijing, China; 2 Department of Neurology and 3 Center for Neuroscience and Re- generation Research, Yale University School of Medicine, New Ha- ven; 4 Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, CT; 5 Department of Dermatology, Peking University First Hospital; and 6 Department of Dermatology, Beijing Children Hospital, Beijing, China. Received Sep 27, 2005, and in revised form Oct 27. Accepted for publication Nov 4, 2005. C.H. and A.M.R contributed equally to this study. Published online Jan 3, 2006, in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ana.20776 Address correspondence to Dr Waxman, Department of Neurology, LCI 707, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06510. E-mail: stephen.waxman@yale.edu or Dr. Yang, Depart- ment of Dermatology, Peking University First Hospital, No. 8. Xish-iku Street, Xicheng District, Beijing, 10034, China. E-mail: yongyang81@yahoo.com.cn © 2006 American Neurological Association 553 Published by Wiley-Liss, Inc., through Wiley Subscription Services