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Alport syndrome

What is Alport syndrome?

Alport syndrome is a genetic condition characterized by kidney disease, hearing loss, and eye abnormalities. Almost all affected individuals have blood and protein in their urine, which indicates abnormal function of the kidneys. As the condition progresses, kidney function declines, possibly leading to end stage kidney disease (ESKD). Affected individuals can also develop significant hearing loss and eye abnormalities that do not affect vision.

Alport syndrome is categorized into three types depending on the genetic basis: X-linked Alport syndrome (XLAS), autosomal recessive Alport syndrome (ARAS), and autosomal dominant Alport syndrome (ADAS).

 

 

Alport syndrome is a genetic condition characterized by kidney disease, hearing loss, and eye abnormalities. Almost all affected individuals have blood and protein in their urine, which indicates abnormal function of the kidneys. As the condition progresses, kidney function declines, possibly leading to end stage kidney disease (ESKD). Affected individuals can also develop significant hearing loss and eye abnormalities that do not affect vision.

Alport syndrome is categorized into three types depending on the genetic basis: X-linked Alport syndrome (XLAS), autosomal recessive Alport syndrome (ARAS), and autosomal dominant Alport syndrome (ADAS).

 

Acknowledgement of Alport syndrome has not been added yet.

Alport syndrome is a genetic condition that affects the kidneys, hearing, and eyesight. The prevalence of Alport syndrome is approximately 1 in 50,000 newborns. In the case of XLAS, women are more likely to be mildly affected, and men typically have more severe disease, however both are at risk of developing ESKD. ARAS and ADAS affect males and females equally. Approximately 0.2% of adults and 3% of children in the United States that have end stage kidney disease have Alport syndrome.

Alport syndrome is diagnosed by testing the urine, kidney function, and hearing. Confirmation of Alport syndrome can be done with a kidney biopsy or skin biopsy in some patients.  A kidney biopsy is a test where a sample of the kidney tissue is taken out with a small needle and examined microscopically for diagnosis. Genetic testing can also confirm a diagnosis of Alport syndrome.

Synonyms for Alport syndrome has not been added yet.

Alport syndrome can be an autosomal dominant, recessive, or X-linked inherited disorder depending on the gene affected.  ARAS and ADAS  are caused by mutations or changes in either the COL4A3 or COL4A4 genes, and XLAS by changes in the COL4A5 gene.

These genes are responsible for making an important protein called type IV collagen. Webs of collagen in the glomeruli (part of the kidneys) play an important role in the body’s waste filtration system. In Alport syndrome, the type IV collagen fiber is either abnormal or missing, so the body naturally attempts to repair the weakened glomeruli. Over time, the glomeruli become scarred and damaged, and kidney function progressively declines.

Type IV collagen also plays an important role in inner ear structures, specifically the cochlear membrane. The cochlear membrane is responsible for transmitting sound waves to the nerve sensors of the ear. Abnormal type IV collagen causes weakened inner ear function, which leads to progressive hearing loss.

Type IV collagen is present in the eyes as well. It maintains the shape of the lens and the normal color of the retina. Abnormal type IV collagen causes abnormal shape of the lens and abnormal color of the retina.

There are different types of inherited Alport syndrome: X-linked Alport syndrome, autosomal recessive Alport syndrome, and autosomal dominant Alport syndrome.

X-linked Alport syndrome:   Mutations at the COL4A5 gene is the most common and is located on the X chromosome. Just one mutated COL4A5 gene is enough to cause kidney disease. A characteristic of mutations at the COL4A5 gene is that fathers cannot pass it to their sons.

Autosomal dominant or recessive Alport syndrome: Mutations at the COL4A3 or the COL4A4 gene occur less commonly. They are inherited in an autosomal dominant or recessive pattern. When it is autosomal dominant, only one copy of the gene is needed for Alport syndrome to occur. In other words, only one parent is a carrier (an individual who has one abnormal copy of the gene and one normal copy of the gene). When it is autosomal recessive, each parent of the affected individual each is a carrier. Carriers typically have mild or no symptoms. Some may test positive for blood or protein in their urine only.  Some may develop kidney disease or failure.

The severity of symptoms differs based on age, gender, and inheritance type.

Alport syndrome affects the kidneys, hearing, and eyesight. An early indication of Alport syndrome is blood in the urine, without pain. In young boys, it is common to see droplets of blood mixed into the urine. More commonly, the blood is mixed into the urine and invisible. Blood in the urine can only be confirmed by looking at the urine under a microscope or by a urine stick test. Protein in urine is also common. It is possible to have protein and blood in the urine and have normal functioning kidneys.  Most men with Alport syndrome do not develop kidney failure until their twenties or thirties.

Hearing problems in young boys typically manifests around the age of ten. This is around the same time that signs of kidney dysfunction begin to develop. Once hearing loss begins, it slowly progresses. Because hearing loss is normal during birth, speech develops normally. Women are more likely to develop hearing loss rather than kidney failure, but both can still happen later in life.

Eyesight problems are usually mild. They are more common in adults than children. Small white flecks are seen in the eyes. There is no effect on vision but these symptoms can help diagnose Alport syndrome. In some affected individuals, the lenses becomes misshapen.

Other symptoms of Alport syndrome include: high blood pressure and swelling in the legs, ankles, feet, and around the eyes. Swelling occurs because of fluid buildup in the tissues (edema) that results from declining kidney function.

 

Diagnosis of Alport syndrome is based on family history, kidney failure without known cause, and early hearing loss or hematuria.

Genetic testing is recommended if there is a family history of Alport syndrome or if the clinical symptoms strongly suggestion the diagnosis. This can confirm diagnosis and help to determine the type of Alport syndrome, or determine if a person is at risk of passing a mutation on to their children.

Urine tests can confirm if blood and/or protein is present in the urine.

Blood tests can confirm the amount of protein in the blood and the kidney function.

Glomerular Filtration Rate (GFR) can determine how well the kidney is functioning.

Kidney biopsy can confirm Alport syndrome by examining a piece of kidney tissue under a microscope.

Hearing tests can confirm hearing loss for high frequency, which is required for understanding speech.

Vision tests can determine if vision has been affected.

There is no specific treatment for Alport syndrome. Most medications are used to help slow the progression of kidney disease and treat symptoms. High blood pressure medications called Angiotensin Converting Enzyme (ACE) inhibitors or Angiotensin Receptor Blockers (ARBs) are commonly used.  These medications protect the kidney by decreasing the blood pressure around the glomeruli, reducing the scarring and damage, and are recommended for all patients with Alport syndrome and protein in their urine, regardless of blood pressure. Medications such as diuretics (“water pills”) can help reduce symptoms of swelling. Reducing salt intake can help decrease blood pressure and damage to the kidney. Hearing aids can help with hearing loss. Misshaped lenses can be replaced.

There are different stages of kidney disease ranging from mild to severe. When an affected individual has severe kidney disease or end stage kidney disease, preparation for a transplant or dialysis should be considered.

 

Early detection is important to delay progression.  Awareness of risk factors and family history allows the condition to be detected early on. Men with X-linked Alport syndrome commonly develop hearing loss, vision problems, and end stage kidney disease by age 50.

Tips or Suggestions of Alport syndrome has not been added yet.

“Alport Syndrome” National Kidney Foundation (2017). https://www.kidney.org/atoz/content/alport

“Alport Syndrome Medical Encyclopedia” NIH U.S. National Library of Medicine – MedlinePlus (2018). https://medlineplus.gov/ency/article/000504.htm

“Alport Syndrome” NIH U.S. National Library of Medicine (2018).  https://ghr.nlm.nih.gov/condition/alport-syndrome#synonyms

“Alport Syndrome – Patient Information.” Rare Renal – Information on rare kidney disease (2018) http://rarerenal.org/patient-information/alport-syndrome/

Kashtan, CE. “Alport Syndrome and Thin Basement Membrane Nephropathy” GeneReviews (2001). https://www.ncbi.nlm.nih.gov/books/NBK1207/

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