Erythromelalgia (Erythromelalgia) - Gen SCN9A

Erythromelalgia is a disorder characterized by episodes of pain, redness and swelling in various parts of the body, particularly the hands and feet. These episodes are usually caused by increased body temperature following exercise or when entering a warm room. Drinking alcohol or spicy foods can also trigger an episode. The use of warm socks, tight shoes or gloves can cause an episode of debilitating pain that can impede daily activities such as wearing shoes and walking.

Signs and symptoms of erythromelalgia usually begin in childhood, although mildly affected individuals may have their first episode of pain later. As these individuals age and the disease progresses, hands and feet can be constantly red, and areas affected can spread from the hands to the arms, shoulders and face, and from the feet to all the legs. Often, erythromelalgia is considered a form of peripheral neuropathy, affecting the peripheral nervous system, connecting the brain and spinal cord to the muscles and the cells that detect sensation like touch, smell , and pain.

An estimated 15 percent of cases of erythromelalgia are due to mutations in the SCN9A gene (sodium voltage-gated channel alpha subunit 9), located on the long arm of chromosome 2 (2q24). It is believed that no other cases have a genetic cause or may be caused by mutations in one or more genes not yet identified. The SCN9A gene belongs to a family of genes encoding sodium channel. These channels, which transport sodium ions into cells, play a key role in the ability of a cell to generate and transmit electrical signals. In particular, the SCN9A gene encodes the alpha subunit of a sodium channel Nav1.7 known, found in nociceptors. The nociceptors are part of the peripheral nervous system connecting the brain and spinal cord cells that detect sensation like touch, smell , and pain. Nociceptors are mainly involved in the transmission of pain signals. Nociceptors centers, known as the cell bodies are found in the dorsal root ganglion. Axons extending from the cell bodies, reaching the whole organism to receive sensory information. Axons transmit information back to the dorsal root ganglion, which is then sent to the brain. Nav1.7 sodium channels are also found in olfactory sensory neurons.

They have identified more than 10 mutations in the gene responsible for erythromelalgia SCN9A. All identified mutations change the amino acids in Nav1.7 sodium channel. These mutations result in a sodium channel Nav1.7 that is more easily opened and remains open longer than usual, increasing the flow of sodium ions producing nerve impulses inside nociceptors. This increase in sodium ions improves the transmission of pain signals, leading to the signs and symptoms of erythromelalgia.

Some cases of erythromelalgia are inherited in an autosomal dominant pattern, which means that a copy of the altered gene in each cell is sufficient for alteration is expressed. In some of these cases, an affected person inherits the mutation from an affected parent. Other cases are due to new mutations in the gene and occur in people with no history of disease in your family.

Tests in IVAMI: in IVAMI perform detection of mutations associated with erythromelalgia, by complete PCR amplification of the exons of the SCN9A gene, and subsequent sequencing.

Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).