 This is a prospective, non-randomized, non-blinded observational study. The overarching goal is to discover new disease-associated genes in children, while establishing a specific focus on disorders where molecular characterization is most likely to lead to novel therapies. This study will merge detailed phenotypic characterization of patients presenting to the Pediatric Genetics and Metabolism Division in the Department of PediatricsChildrens Medical Center at Dallas and collaborating clinics with Next-Generation sequencing techniques to identify disease-producing mutations. The primary objective of the study is to identify novel pathogenic mutations in children with rare Mendelian disorders. A secondary objective of the study is to establish normative ranges of a large number of metabolites from healthy newborns and older children. 