Approach to adult-onset mendelian disorders

Adult-Onset Mendelian disorders are diverse clinical conditions arising from pathogenic variations in single genes or loci and can involve any organ systems. These rare disorders are often challenging to recognize and diagnose; however, the advancement in genetic sequencing technology has significantly improved the diagnostic ability, broadened the clinical spectrum of disease, and facilitated novel therapies. In this chapter we differentiate between monogenic disorders and polygenic disorders, analyze the nature of adult-onset phenotypes for Mendelian disorders, describe the process of clinical evaluation, review the different modalities for testing, and briefly discuss the different aspects of management including novel and emerging therapies.