Hunter syndrome is a lysosomal storage disease that is inherited in an X-linked recessive manner and therefore mainly affects male offspring.

X linked recessive inheritance

Aside from the gamete cells, all cells in the human body contain 46 chromosomes, with 23 inherited from each parent. One pair of these chromosomes are the sex chromosomes (the X and Y chromosomes). Females have two X chromosomes, whereas males have one X chromosome and one Y chromosome.

Hunter syndrome is inherited through a mutation in the I2S gene on the X chromosome. Since males only have one X chromosome, they will develop symptoms of the condition if that chromosome carries the mutation. However, because the condition is recessive, the inheritance of one abnormal X chromosome does not usually cause symptoms in females because they usually also inherit another normal X chromosome. These females are then classified as carriers of the disease and can pass on the mutation to male offspring even though they do not develop symptoms themselves.

Prenatal testing can be carried out to check whether a child carries a copy of the defective gene using either a sample from the amniotic fluid (amniocentesis) or a sample from the placenta (chorionic villus sampling).

Genetic testing and genetic counselling are available for couples with a family history of Hunter syndrome who may want to determine how likely it is their child will be born with the condition.