Central Diabetes Insipidus (CDI) 15035X Mutations Clinical Use Clinical Background • Differentiate inherited CDI from CDI is an acquired or autosomal acquired CDI dominant inherited disorder character- • Screen for CDI carrier status in at- ized by polyuria, polydipsia, a low risk individuals urinary specific gravity, and high risk of severe dehydration. Arginine Reference Range vasopressin (AVP), also known as Negative (no mutations detected) antidiuretic hormone (ADH), is absent. CDI stems from the degenera- Interpretive Information tion or destruction of cells in the posterior pituitary, the site of AVP Mutation present production. Thus, it is also referred to • Central diabetes insipidus (affected as pituitary, neurohypophyseal, or or carrier) neurogenic diabetes insipidus. The disorder typically presents in infancy or early childhood, although late-onset cases have been reported. Although rare, inherited CDI can be caused by mutations in the AVP gene on chromosome 20. Prepro-AVP, the initial protein product of the AVP gene, undergoes several post-transla- tional steps to yield AVP, neurophysin, and glycoprotein. When mutations in the AVP gene are present, cytotoxic products that lead to destruction of the secretory neurons are generated. Since more than 30 relevant mutations have been identified, gene sequencing is the method of choice for diagnosis of the inherited form. After identifica- tion of a mutation in an affected indi- vidual, genetic testing can be used to evaluate other family members. Method • Polymerase chain reaction (PCR) and DNA sequencing • Analytical specificity: mutations in 3 exons of the AVP gene Specimen Requirements 5 mL room temperature whole blood 3 mL minimum Collect blood in a lavender-top (EDTA) or yellow-top (ACD solution B) tube. 46.