Serological characterization can easily distinguish human ERPV from ectromelia virus and vaccinia virus by cross-neutralization and plaque reduction assays Since this virus has not yet been isolated from other outbreaks in other parts of southern China to date this putative association needs to be further investigated. The finding of the specific antibody conversion to ATIs of ERPV in patients paired sera strengthens the evidence for a possible aetiological role of human ERPV in epidemic erythromelalgia. Pathophysiology
There are 10 known mutations in the voltage-gated sodium channel α-subunit NaV1.7 encoding gene, SCN9A. This channel is expressed primarily in nociceptors of the dorsal root ganglion and the sympathetic ganglion neurons. Nine of these mutations have received further study and they have all shown to result in similar biophysical alterations, Table 1. As can be seen from table 1, the primary effect of erythromelalgia mutations is NaV1.7 channels that activate at more hyperpolarized potentials. NaV1.7 channels act largely as threshold sensors and initiate action potentials. Consequently, this shift in their activation profile results in channels that open closer to the resting membrane potential. In many mutations, this shift of activation is accompanied by shifts in the voltage sensitivity of fast and/or slow inactivation, often in the depolarized direction. This results in channels that are open for a longer of period of time, producing larger and more prolonged changes in membrane potential.Some of these mutant channels have been expressed in dorsal root ganglion (DRG) or sympathetic neurons.
A parasitic twin, also known as an asymmetrical or unequal conjoined twin, is the result of the processes that also produce vanishing twins and conjoined twins, and may represent a continuum between the two. Parasitic twins occur when a twin embryo begins developing in utero, but the pair does not fully separate, and one embryo maintains dominant development at the expense of its twin. Unlike conjoined twins, one ceases development during gestation and is vestigial to a mostly fully formed, otherwise healthy individual twin. The undeveloped twin is defined as parasitic, rather than conjoined, because it is incompletely formed or wholly dependent on the body functions of the complete fetus. The independent twin is called the autosite. Variants
Conjoined parasitic twins joined at the head are described as craniopagus or cephalopagus, and occipitalis if joined in the occipital region or parietalis if joined in the parietal region. Craniopagus parasiticus is a general term for a parasitic head attached to the head of a more fully developed fetus or infant. Fetus in fetu sometimes is interpreted as a special case of parasitic twin, but may be a distinct entity. The twin reversed arterial perfusion, or T.R.A.P. sequence, results in an acardiac twin, a parasitic twin that fails to develop a head, arms and a heart. The parasitic twin, little more than a torso with or without legs, receives its blood supply from the host twin by means of an umbilical cord-like structure, much like a fetus in fetu, except the acardiac twin is outside the autosites body.