Profound iduronate sulfatase deficiency, characteristic of the Hunter syndrome, 
has been found in cultured fibroblasts, serum, lymphocytes, and tissues of two 
clinically affected girls. The patients are karyotypically normal and have 
normal fathers; cloning of the mothers' fibroblasts did not reveal the mosaicism 
expected of carriers of an X-linked disease. Homozygosity for a previously 
unsuspected autosomal recessive gene for iduronate sulfatase is considered the 
most likely explanation, although heterozygosity for the X-linked gene and 
subsequent selection cannot be completely excluded.