Fig. 1
From: Treatable inherited metabolic disorders causing intellectual disability: 2021 review and digital app
Diagnostic algorithm for treatable IDs. 1st Tier consists of non-targeted metabolic screening tests that are readily available in most developed countries. 2nd Tier consists of targeted metabolic tests, often more invasive and/or less available. Some IMDs are identified by multiple (screening) tests in the 1st and 2nd Tier. Genetic testing (targeted molecular analysis as well as exome sequencing) can be performed in parallel. (ID = Intellectual disability; IMD = Inherited Metabolic Disorder)