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Alport syndrome


Other Names for this Disease
  • Alport syndrome, X-linked
  • Congenital hereditary hematuria
  • Hemorrhagic familial nephritis
  • Hemorrhagic hereditary nephritis
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Overview



What is Alport syndrome?

What causes Alport syndrome?

How is Alport syndrome inherited?

How might Alport syndrome be treated?


What is Alport syndrome?

Alport syndrome is a genetic condition characterized by kidney disease, hearing loss, and eye abnormalities. Most affected individuals experience progressive loss of kidney function, usually resulting in end-stage kidney disease. People with Alport syndrome also frequently develop sensorineural hearing loss in late childhood or early adolescence. The eye abnormalities seen in this condition seldom lead to vision loss. In 80% of cases, Alport syndrome is inherited in an X-linked manner and is caused by mutations in the COL4A5 gene. In the remaining cases, it may be inherited in either an autosomal recessive or autosomal dominant manner and caused by mutations in the COL4A3 or COL4A4 genes.[1] Treatment may include use of a hearing aid; hemodialysis and peritoneal dialysis to treat those with end-stage renal failure; and kidney transplantation.[2]
Last updated: 8/1/2013

What causes Alport syndrome?

Alport syndrome may be caused by mutations in either the COL4A3, COL4A4, or COL4A5 genes. These genes each provide instructions for making one component of a protein called type IV collagen, which plays an important role in the glomeruli of the kidneys. Glomeruli are clusters of specialized blood vessels that remove water and waste products from the blood and create urine. Mutations in the genes mentioned above result in abnormalities of the type IV collagen in glomeruli, which prevents the kidneys from properly filtering the blood. As a result, blood and protein pass into the urine. Over time, the kidneys become scarred and many people with Alport syndrome develop kidney failure.[1]

Type IV collagen is also an important component of the organ of Corti, an inner ear structure that transforms sound waves into nerve impulses for the brain. Alterations in type IV collagen may result in abnormal inner ear function, which can lead to hearing loss. In addition, type IV collagen plays a role in the eye, where it helps maintain the shape of the lens and the normal color of the retina. Mutations found in Alport syndrome may affect the shape of the lenses and the color of the retina.[1]

Last updated: 8/1/2013

How is Alport syndrome inherited?

Alport syndrome can have different inheritance patterns. About 80 percent of cases are caused by mutations in the COL4A5 gene and are inherited in an X-linked recessive pattern. This gene is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the COL4A5 gene in each cell is sufficient to cause kidney failure and other severe symptoms of the disorder. In females (who have two X chromosomes), a mutation in only one copy of the COL4A5 gene usually only results in hematuria, but some women experience more severe symptoms. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.[1]

In approximately 15 percent of cases, Alport syndrome results from mutations in both copies of the COL4A3 or COL4A4 gene and is inherited in an autosomal recessive pattern. The parents of an individual with the autosomal recessive form of this condition each have one copy of the mutated gene and are called carriers. Some carriers are unaffected and others develop a less severe condition called thin basement membrane nephropathy, which is characterized by hematuria.[1]

Alport syndrome has an autosomal dominant pattern of inheritance in about 5 percent of cases. People with this form of Alport syndrome have one mutation in either the COL4A3 or COL4A4 gene in each cell. It remains unclear why some individuals with one mutation in the COL4A3 or COL4A4 gene have autosomal dominant Alport syndrome and others have thin basement membrane nephropathy.[1]

Last updated: 8/1/2013

How might Alport syndrome be treated?

Although there is no one specific treatment for Alport syndrome, the goals of treatment include monitoring and controlling progression of the disease and treating the symptoms. Strict control of blood pressure is very important. Research suggests that ACE inhibitors can help reduce proteinuira and the progression of kidney disease.[3] However, treatment of chronic kidney failure often becomes necessary. This can include dietary modifications, fluid restriction, and other treatments. Ultimately, chronic kidney failure progresses to end-stage kidney disease, requiring dialysis or transplantation.[4] Kidney transplantation in patients with Alport syndrome is usually successful, but some studies have reported that about 10% of transplanted patients develop nephritis in the graft.[5]

Other aspects of the condition are addressed as needed. For instance, surgical repair of cataracts (cataract extraction), or repair of the anterior lenticonus in the eye may be needed. Loss of hearing is likely to be permanent. Counseling and education to increase coping skills can be helpful. Learning new skills such as lip reading or sign language may be of some benefit. Hearing aids are helpful. Young men with Alport syndrome should use hearing protection in noisy environments. Genetic counseling may be recommended because of the inherited pattern of the disorder.[4]

Additional information related to the treatment of Alport syndrome can be accessed through GeneReviews and eMedicine

Last updated: 1/30/2014

References
  1. Alport syndrome. Genetics Home Reference. April 2009; http://ghr.nlm.nih.gov/condition/alport-syndrome. Accessed 10/24/2011.
  2. Mietta Meroni and Adalberto Sessa. Alport syndrome. Orphanet. July 2007; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=EN&Expert=63. Accessed 8/1/2013.
  3. Ramesh Saxena, MD, PhD. Alport Syndrome. Medscape Reference. August 12, 2013; http://emedicine.medscape.com/article/238260-treatment#showall. Accessed 1/30/2014.
  4. Dugdale DC, Lin HY. Alport syndrome. MedlinePlus. 2009; http://www.nlm.nih.gov/medlineplus/ency/article/000504.htm. Accessed 7/12/2011.
  5. Sessa A, Meroni M. Alport syndrome. Orphanet. 2007; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=EN&Expert=63. Accessed 7/12/2011.