Neurologists should consider the possibility of an inherited metabolic disorder in adults with neurologic symptoms that may or may not mimic those seen in affected children, such as in the case of biotinidase deficiency. Because many of these disorders are treatable, they must be included in the differential diagnosis. Technologies, such as specific biochemical analysis and whole exomic sequencing, can assist the clinician by leading to the appropriate diagnosis and treatment. Whole exomic sequencing can identify known and putative mutations in a patient's genome. The neurologist must “think metabolic” in sorting out complex and difficult cases.