HOOD syndrome is a rare genetic disorder also known as nail patella syndrome. Biochemical and molecular biological data are rare and not conclusive. Preliminary data suggest the involvement of collagen type IV. This would, however, not be enough to explain nail or bone involvement. As kidney pathology would be consistent with a cross-linking disorder, we tested collagen IV and kidney collagen cross-linking on SDS-PAGE. This method showed a remarkable reduction in high-molecular-weight collagen polymers. The patient’s and his mother’s urinary pyridinoline cross-link excretion was manifold increased. Disturbed cross-linking of connective tissue proteins would help to explain the multiorgan involvement.