Lateral spine radiograph of the father (III,7) showed notching of the anterior end plates of the lumbar vertebrae associated with grade 2 - spondylolisthesis (forward slippage of L5/S1) because of congenital abnormality of the facets and the pars-interarticularis (arrow). Also the father is a heterozygous carrier of disease-causing mutations in the ARSB gene as well as in the GNS gene, which denotes an impaired lysosomal degradation of dermatan sulfate and heparan sulfate in the fully developed diseases MPS VI and MPS IIID.