What Causes Alport’s Syndrome, and differences between men and women?

Collagen is a ‘building block’, giving parts of the body not supported by bone their shape and strength. Cells, tiny packages of tissue that work to make energy and do all the 'work' inside our bodies, have no strength themselves. If cells were not held together, the human body would be like a lump of jelly. Bones are important in giving the human body shape and rigidity, but even soft tissues need holding together. This is the job of collagen.

There are several types of collagen, each of which are found in different parts of the body. Type 4 collagen is important in the kidney, ears and, to a lesser extent, in the eye. Type 4 collagen is abnormal in Alport’s syndrome. The abnormality occurs because the genetic code, which tells the body how to make collagen, is abnormal. In medical shorthand, this is called the COL4A5 gene.

By chance, the type 4 collagen gene is found on the ‘X’ chromosome, which determines the sex of a person. A chromosome is just a package of codes for different tissues of the body, perhaps in the same way that one volume of the Encyclopaedia Britannica contains some information from the whole encyclopaedia in a conveniently sized bundle. The human body has two copies of each chromosome, one from each parent. There are 23 pairs of chromosomes. One pair determines whether a person is male or female. This pair is made up of ‘X’ and ‘Y’ chromosomes. If someone is ‘XX’, they are female. If someone is ‘XY’, they are male. The Y chromosome is smaller than the ‘X’ chromosome, and it so happens that the COL4A5 gene is missing from the ‘Y’ chromosome. Therefore, if a male has a defective COL4A5 gene, there is no normal copy to help produce normal type 4 collagen.

A woman has two ‘X’ chromosomes. If one is abnormal, there is a second copy which is normal to help produce normal type 4 collagen.

This type of inheritance, which is called 'sex linked' is important when family screening is considered.

NKF Controlled Document No. 48, What Causes Alport’s Syndrome, and differences between men and women?, written 2 September 2002. Last reviewed 27 October 2008.

The National Kidney Federation cannot accept responsibility for information provided. The above is for guidance only. Patients are advised to seek further information from their own doctor.

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Page created: 2 September 2002

Last updated: 29 April 2009

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