Hunter disease, Mucopolysaccharidosis type II, is an X-linked recessive 
lysosomal storage disorder caused by a deficiency in iduronate sulfatase 
activity. We studied at molecular level a Neapolitan family with the disease. We 
report, in patient, the delta 139 mutation on the third exon of the gene, on 
female family members, the DNA analysis that allowed to assess or exclude their 
carrier status and on fetal DNA from a pregnancy of patient's mother, a prenatal 
diagnosis that resulted negative.