Attenuated familial adenomatous polyposis
Attenuated familial adenomatous polyposis: An inherited predisposition to colorectal cancer characterized by fewer than 100 adenomatous polyps in the colon and rectum. It is said to be attenuated because there are fewer polyps than in classic familial adenomatous polyposis (FAP). People with attenuated familial adenomatous polyposis (AFAP) also tend to be older at the diagnosis of their polyps (average age of 44 years) and cancer (average age of 56 years), 10 to 15 years later than in classic FAP. The right side of the colon tends to be involved in AFAP and rectal involvement is rare. AFAP is transmitted in an autosomal dominant manner.
People with AFAP often belong to families that also have members with classic FAP. As in FAP, there may also be polyps higher up in the intestinal tract in the duodenum and stomach and an elevated risk of stomach, liver, and breast cancer. And as in FAP, AFAP is associated with mutations in the APC gene (in some cases). APC gene testing can therefore be informative in people suspected of having AFAP. If APC testing is negative, then genetic testing for MYH mutations (another hereditary cause of colorectal cancer) may be warranted.
It has been recommended that AFAP patients have colonoscopy rather than sigmoidoscopy because the adenomatous polyps are predominantly right-sided and beyond the reach of a sigmodoscope. The role for and timing of prophylactic colectomy (precautionary removal of the colon) in AFAP is controversial.
On the molecular level, mutations in the APC gene in FAP and AFAP have been found in three different regions of the gene:
At the 5′ end of the APC gene, spanning exons 4 and 5;
Within exon 9 of the APC gene; and
At the 3′ end of the APC gene.
It has been proposed that mutations in region 1 are associated with a great range in the number of colorectal polyps (from 2 to more than 500) and with the presence of upper intestinal polyps; that mutations in region 2 are associated with the presence of from 1 to 150 colorectal polyps, but no upper intestinal polyps; and that mutations in region 3 are associated with the presence of less than 50 colorectal polyps.
Read Also:
- Attenuated virus
Attenuated virus: A weakened, less vigorous virus. An attenuated virus may be used to make a vaccine that is capable of stimulating an immune response and creating immunity, but not of causing illness.
- Atypical measles syndrome (AMS)
Atypical measles syndrome (AMS): An altered expression of measles, AMS begins suddenly with high fever, headache, cough, and abdominal pain. The rash may appear 1 to 2 days later, often beginning on the limbs. Swelling (edema) of the hands and feet may occur. Pneumonia is common and may persist for 3 months or more. AMS […]
- Ataxia
Poor coordination and unsteadiness due to the brain’s failure to regulate the body’s posture and regulate the strength and direction of limb movements. Ataxia is usually due to disease in the cerebellum of the brain, which lies beneath the back part of the cerebrum.
- AT (in DNA)
AT (in DNA): AT stands for adenine and thymine, a base pair in DNA. The other base pair in DNA is GC (guanine and cytosine).
- Auditory acuity
Auditory acuity: The clarity or clearness of hearing, a measure of how well a person hears. Auditory acuity is measured in order to determine a person’s need for a hearing aid.