Alport syndrome


Alport syndrome

Description, Causes and Risk Factors:

A genetically heterogeneous disorder characterized by nephritis associated with microscopic hematuria and slow progression of renal failure, sensorineural hearing loss, and ocular abnormalities such as lenticonus and maculopathy; autosomal dominant [MIM*104200, MIM*153640, and MIM*153650], autosomal recessive [MIM*203780], and X-linked recessive [MIM*301050 and MIM*303630] forms exist. The X-linked form is caused by mutation in the collagen type IV alpha-5 gene (COL4A5) on chromosome Xq; the autosomal recessive form is due to mutation in the collagen type IV alpha-3 gene (COL4A3) or alpha-4 gene (COL4A4) on 2q.

Abbreviation: AS.

Alport syndrome

Alport syndrome is a genetic disease in which a collagen mutation affects the kidneys, the ears, and the eyes. The prevalence of Alport syndrome is approximately 1 in 50,000 newborns.

It is now known that most cases of AS are caused by a mutation in the collagen gene COL4A5. This gene encodes for the alpha-5 chain of collagen type IV and is located on the X chromosome. Because women have two X chromosomes (XX), affected women usually have one normal copy and one abnormal copy of the gene. Men only have one copy of the X chromosome (XY). If they inherit the COL4A5 mutation, this abnormal copy of the gene is the only copy they have and the effects are more severe.

Type IV collagen is found in basement membranes (BM), which are selective barriers between cells. In the kidney, the glomerular BM filters waste products into the urine while keeping useful molecules within the blood stream. In AS, the abnormal collagen disrupts this filter, leading to the loss of proteins and red blood cells into the urine. Blood in the urine (hematuria) is a sign common to all types of AS. In the ear, abnormal collagen in the cochlea results in a progressive deafness in which the ability to hear high tones is lost first. Abnormal collagen can also affect the lens of the eye.

According to recent research from Germany, "Alport syndrome is a hereditary glomerulopathy due to abnormal composition of the glomerular basement membrane, leading to end-stage renal disease (ESRD). Studies of animal models of AS have suggested a variety of potentially effective therapies, but none of these has been definitely shown to prevent or delay ESRD in human AS."

Symptoms:

The symptoms of Alport syndrome are: Hematuria - there may be a lot of blood that makes the urine turn pink or red, or there may be so little blood that only a urine test (urinalysis) will detect it. Hematuria is usually the first sign of Alport syndrome. Hearing loss and vision problems (more common in males). Other signs of kidney problems, such as swelling (edema) in the ankles, feet, and legs. In children, the edema may be around the eyes (periorbital) or may be all over the body. There may also be protein in the urine (proteinuria), and blood tests may show increases in blood urea nitrogen (BUN) and creatinine.

Diagnosis and Tests:

Several tests can help diagnose Alport syndrome. Hematuria can be detected by urinalysis. A hearing test (audiometry) can check for hearing loss. A sample of kidney tissue (renal biopsy) can be examined under a microscope for the changes present in Alport syndrome. Eye examination can check for vision changes. Other tests may be done to determine the extent of the kidney disease. Genetic tests also are available that can determine whether a person has the defective Alport's gene.

Treatment:

There is no specific treatment for Alport syndrome, so treatment focuses on managing the kidney disease. People whose kidneys do not work well often have to reduce their salt, protein, and fluid intake. They may take medications such as erythropoietin, phosphate binders, and vitamin D. If the kidneys stop working, affected individuals will need dialysis or a kidney transplant.

Alport's syndrome has a genetic link, you may want to seek genetic counseling if you are planning to have children and there is a family history of the disease.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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