On the opposite movement, the mandibles are pushed deeper into the skin by levering against the maxillae. The maxillae do not slip back because the toothed blades grip the skin. The hypopharynx and the labrum are both hollow. Saliva with anticoagulant is pumped down the hypopharynx to prevent clotting, and blood is drawn up the labrum. To understand the mosquito mouthparts, it is helpful to draw a comparison with an insect that chews food, such as a dragonfly. A dragonfly has two mandibles, which are used for chewing, and two maxillae, which are used to hold the food in place as it is chewed. The labium forms the floor of the dragonflys mouth, the labrum forms the top, while the hypopharynx is inside the mouth and is used in swallowing. Conceptually, then, the mosquitos proboscis is an adaptation of the mouthparts that occur in other insects. The labium still lies beneath the other mouthparts, but also enfolds them, and it has been extended into a proboscis. The maxillae still "grip" the "food" while the mandibles "bite" it. The top of the mouth, the labrum, has developed into a channeled blade the length of the proboscis, with a cross-section like an inverted "U". Finally, the hypopharynx has extended into a tube that can deliver saliva at the end of the proboscis. Its upper surface is somewhat flattened so, when the lower part of the hypopharynx is pressed against it, the labrum forms a closed tube for conveying blood from the host.
This means that the defective gene responsible for the disorder is located on an autosome (chromosome 18 is an autosome), and only one copy of the defective gene is sufficient to cause the disorder, when inherited from a parent who has the disorder. Diagnosis
Clinical suspicion for FAP is raised on the basis of a family history of neuropathy and physical exam showing signs of neuropathy. Diagnosis can be made using genetic testing to identify mutations in the TTR gene, but may include other corroborative investigation. Nerve conduction testing typically shows an axonal polyneuropathy, with sensory involvement greater than motor. Superimposed mononeuropathies may also be evident, such as a median mononeuropathy at the wrist (carpal tunnel syndrome). Electromyography (EMG) may show evidence of chronic denervation and reinnervation. Autonomic testing, including quantitative sweat testing, can reveal involvement of the autonomic nervous system. Occasionally, biopsy of skin, nerve, or muscle may be performed, which can show signs of denervation and amyloid deposition with response to anti-TTR antibodies. Additional testing should be performed to identify involvement of the heart or kidneys.Sudomotor function through electrochemical skin conductance may provide a measure of subclinical autonomic involvement. Treatments
The medication tafamidis has been approved for the treatment of transthyretin familial amyloid polyneuropathy in Europe. Studies have found that it delays neurological problems when started early. The US Food and Drug Administrations Peripheral and Central Nervous System Drugs Advisory Committee rejected the drug in June 2012, in a 13-4 vote.