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Wednesday 24 July 2019
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How the Diseases are Inherited

There are two different ways all Lysosomal Storage disorders are inherited the first being autosomal recessive inheritance which covers all but three L.S.Disorders which are Fabry Disease, MPS II and Danon Disease these are x linked disorders.

 

Here is visual image of how a LSD is inherited by autosomal recessive inheritance:

 

autosomal recessive inheritance

Almost all the genes in the human body come in pairs, one inherited from each parent. A carrier of a recessive condition has one copy of the gene which is altered (a mutation) but also has a normal copy of the gene (the dominant copy). Most people are unaware that they carry genes for a disease until they have an affected child, as the carriers usually have no clinical features of the disease.

 

If both parents are carriers of a condition, there is a 1:2 (50%) chance of the child also being a carrier, a 1 in 4 (25%) chance of the child not having the disease or being a carrier and 1:4 (25%) chance of the child having the disease. Males and females are equally likely to be affected.

 

If only one parent is a carrier, there is no chance of the child having the condition; however, there is a 1:2 chance in each pregnancy that the child will be a carrier.

 

Here is visual image of how a LSD is inherited by x- linked inheritance:

 

x- linked inheritance

The sex chromosomes come in two types, X and Y. Females have two X chromosomes (XX) and males an X and a Y chromosome (XY).

 

In X-linked inheritance, the abnormal gene is on the X chromosome. These conditions tend to be more common among males because if the affected gene is on the X (female) chromosome there is no dominant allele to 'hide' or counteract it on the Y (male) chromosome. But if the gene is dominant then girls may be affected. For females to inherit an X-linked recessive condition they must inherit two copies of the recessive allele, one from each parent, whereas the boys need only one copy of the recessive gene to develop disease.

 

For an X-linked condition, for each pregnancy, the inheritance chances are:

  • affected boy: 1:4 (25%) chance

  • unaffected boy: 1:4 (25%) chance

  • female carrier 1:4 (25%) chance

  • female, non-carrier: 1:4 (25%) chance