Mucopolysaccharidosis VII (GUSB)
Mucopolysaccharidosis type VII (MPS VII), also known as Sly syndrome, is a rare autosomal recessive disorder caused by pathogenic variants in the gene GUSB. This disorder is caused by a deficiency of β-glucuronidase, leading to the accumulation of GAGs inside cellular structures called lysosomes. The severity and onset of this condition vary. The most severe cases present prenatally with hydrops fetalis and typically end in stillbirth or neonatal death. Less severe cases of MPS VII present during early childhood and have a life expectancy into adolescence and adulthood. Common characteristics include coarse facial features, hydrocephalus, macrocephaly, cognitive impairment, hepatosplenomegaly, macroglossia, heart valve abnormalities, umbilical hernia, carpal tunnel syndrome, spinal stenosis, and sleep apnea. Hallmark features are corneal clouding which leads to significant vision loss and multiple skeletal abnormalities seen on x-ray (dysostosis multiplex). The life expectancy depends on the severity of the condition. Heart disease and airway obstruction are major causes of death in individuals with MPS VII. No clear genotype-phenotype correlation has been established.
For information about carrier frequency and residual risk, please see the residual risk table.