NANS and skeletal dysplasia: An example of this approach is our group’s recent study, which used untargeted metabolomics to demonstrate that a bi-allelic variant in N-acetylneuraminic acid synthase (NANS) in patients with infantile-onset severe developmental delay and skeletal dysplasia was reflected in high levels of N-acetylneuraminic acid (Van Karnebeek et al, 2016).