How MPS VI is Inherited - A Primer for Parents
MPS VI is a rare disease: it happens in only about 1 out of every 340,000 live births.1,2
MPS VI is caused by an inherited genetic change that causes a person to be deficient in the
enzyme arylsulfatase B (ASB). To understand how MPS VI is inherited, it is important to learn a
little about genetics.
Our genes carry the instructions for traits like eye color and hair color as well as a multitude of
instructions that our body needs to function properly, including instructions to make ASB and all
other enzymes.
We inherit genes in pairs—one copy from our mother and one copy from our father. People who
have one working ASB gene and one nonworking gene are called carriers; they make enough
ASB to remain healthy, and do not have MPS VI disease. Individuals who have MPS VI have,
simply by chance, inherited 2 nonworking copies of the ASB gene—one from each parent.
 Because MPS VI is so rare, it is unlikely (unless there is a family history of MPS VI—which there
almost never is) that an individual would be a carrier of MPS VI. A prospective parent would have
no reason to think that he or she might be an MPS VI carrier. However, once a couple has a child
diagnosed with MPS VI they learn that they are both MPS VI carriers and that, by chance, each
passed their nonworking copy of the ASB gene on to their affected child. This type of inheritance,
where 2 nonworking genes must be present in order for the disease to occur, is called recessive
inheritance. MPS VI parents should not feel as though they could have known or done anything to
prevent MPS VI. We are all carriers of a few nonworking genes and have no way of knowing until,
by chance, a disease occurs.
If only one parent is a carrier of the nonworking gene, it is not possible to have a child with MPS
VI. If both parents happen to be carriers, then for each pregnancy, there is a 1 in 4 chance that
the child will have MPS VI. This pattern of genetic inheritance, in which a child must have 2
nonworking copies of a gene to develop a disease, is called autosomal recessive inheritance.
Genetic counseling is recommended to help parents understand autosomal recessive inheritance
and the chance of MPS VI occurring in future pregnancies, as well as the significance of MPS VI
for unaffected siblings.
- Meikle PJ, Hopwood JJ, Clague AE, Carey WF. Prevalence of lysosomal storage disorders. JAMA.
1999;281:249-254.
- Poorthuis BJ, Wevers RA, Kleijer WJ, et al. The frequency of lysosomal storage diseases in The
Netherlands. Hum Genet. 1999;105:151-156.
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