Inheritance of Maroteaux-Lamy (MPS VI)

MPS VI is a single-gene disorder caused by an inherited mutation in the gene encoding arylsulfatase B (ASB), which results in abnormally low levels of ASB enzyme activity. The ASB gene locus has been mapped to chromosome 5.^1,2

Inheritance of MPS VI

MPS VI is inherited in an autosomal recessive manner; the disease is expressed only in individuals who are homozygous for the mutant allele. Heterozygous carriers do not develop MPS VI themselves; with 1 functional copy of the gene present, they still produce enough active ASB enzyme to avoid developing clinical disease.¹

The diagram illustrates the probability of inheriting MPS VI when both parents are carriers. With each pregnancy, there is a 1 in 4 (25%) chance of passing on the disease allele (r) from both parents, producing a child who is homozygous for the disease allele (rr) and therefore affected by MPS VI.

Each pregnancy also carries a 2 in 4 (50%) chance of the child inheriting 1 copy of the disease allele and 1 copy of the normal allele (Rr) and therefore being a carrier who is clinically unaffected.

Finally, if both parents are carriers, there is a 25% chance for each pregnancy that both parents will pass on the normal allele, producing an unaffected non-carrier.

1. Neufeld EF, Muenzer J. The mucopolysaccharidoses. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The Metabolic and Molecular Bases of Inherited Disease. Vol 3. 8th ed. New York, NY: McGraw- Hill; 2001:3421-3452.
2. Litjens T, Baker EG, Beckmann KR, et al. Chromosomal localization of ARSB, the gene for human N-acetylgalactosamine- 4-sulphatase. Hum Genet. 1989;82:67-68.