There are three different types of inheritance. These will often determine the age onset of symptoms and their severity, although it is now known that patient experiences vary and that several factors, such as lifestyle and other inherited traits, may influence how and when symptoms will occur.

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X Linked Alport syndrome (XLAS)

 

80% of individuals diagnosed with Alport syndrome.

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X Linked Alport Syndrome (XLAS) is the result of an inherited mutated gene on an X chromosome.

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We all have two 'sex chromosomes' , known as X and Y. The X chromosome is called the female sex chromosome, and the Y chromosome is called the male sex chromosome.

 

Females have two X chromosomes (XX), and males have one X and one Y chromosome (XY). We inherit only one of these chromosomes from each parent, thus determining whether are  born female (XX) or male (XY).

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Males (XY) inherit either one of their mother's X chromosomes, and from their father they inherit only his Y chromosome.

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Females (XX) inherit either one of their mother's X chromosomes, and from their father they inherit only his X chromosome.

 

Either parent may have a mutated gene carried on their female sex chromosome, XLAS.  This explains why the disease is usually more severe in men (XY) than in women (XX), as generally if females inherit one 'mutated' XLAS chromosome from their affect parent they will also inherit one 'good' X chromosome from their other parent which provides a varying degree of protection from severe symptoms and slows down the progression of the disease.

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Males can only inherit X Linked Alport syndrome from an affected mother carrying the XLAS. Males cannot inherit the XLAS from their father because males only inherit the Y chromosome (the male sex chromosome) from their father. For the same reason, an affected father cannot pass X Linked Alport syndrome on to his sons because they inherit only his Y chromosome.

 

There is a 50% chance a male will inherit the XLAS chromosome from his affected XLAS mother, and a 50% chance he will instead inherit her unaffected X chromosome, and therefore not have Alport Syndrome.

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However, a female can inherit the mutated gene from an affected XLAS mother or from an affected father.

 

There is a 50% chance a female will inherit the XLAS chromosome from her affected XLAS mother, and a 50% chance she will instead inherit her mother’s unaffected X chromosome, and therefore not be affected by Alport Syndrome.  

 

But it is certain a female will inherit the XLAS chromosome from an affected father. Fathers must pass on the XLAS (their only female sex chromosome) to all female children.

 

Keep in mind that women have two X chromosomes and so will inherit an unaffected X chromosome from the unaffected parent. This is why is it very important that when a family member is diagnosed with Alport syndrome all the related women should consider genetic testing whether they show symptoms or not.

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X Linked Alport syndrome usually progresses more rapidly in males than females, and symptoms are often diagnosed at an earlier age in men than women.

 

Renal failure, or 'end stage renal disease' (ESRD) usually occurs in males between the ages of 30 and 50.  However, the renal function of females may never require them to undergo dialysis nor renal transplant.

See below on this page “Transfer Rules for XLAS to the Next Generation” for further explanation and a diagrammatic representation.

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Autosomal Recessive Alport syndrome (ARAS)

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About 15% of individuals with Alport syndrome..

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Autosomal Recessive Alport Syndrome (ARAS) may be inherited when a mutated gene occurs on a numbered chromosome rather than a sex chromosome, known as an 'autosome', numbered roughly in relation to its size. The word 'recessive' means the mutated gene will be overridden by a working gene or normal gene inherited from the other parent. 

 

Humans have two copies of every chromosome (22 pairs of autosomes and one pair of sex chromosomes -XX or XY). One copy of each is passed on to the offspring.

 

For an individual, male or female, to develop symptoms of Alport syndrome, they must receive a recessive mutated gene from both parents. In other words, both parents are carriers.

 

Both males and females who are affected with Autosomal Recessive Alport syndrome may develop any or all symptoms of the disease, and possibly end stage renal disease (ESRD) by the age of 30.

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If an individual inherits only one mutated recessive gene from a parent, then he/she is a carrier of Alport syndrome, but will not usually develop symptoms of the disease.

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Autosomal Dominant Alport syndrome (ADAS)

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Quite rare, about 5% of individuals with Alport syndrome.

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Autosomal Dominant Alport syndrome (ADAS) is inherited when a mutated gene exists on one of the numbered chromosomes rather than a sex chromosome, known as an 'autosome'. The word 'dominant' means the mutated gene will override (dominate) the working or normal gene inherited from the other parent.

 

Humans have two copies of every chromosome (22 pairs of autosomes and one pair of sex chromosomes -XX or XY). One copy of each is passed on to the offspring.

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If an individual inherits only one mutated dominant gene from a parent, then he or she will have symptoms of Alport syndrome. However, this form of the disease progresses more slowly than other forms.

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