Clinical Genetics is the field studying the inheritance and causes of genetic disorders. A genetic disorder is defined as a pathological condition caused by an absent or defective gene or by a chromosomal aberration. Knowing the cause of a genetic disorder can be of crucial importance, not only for the patient, but also for his or her family. This chapter describes the use of several molecular methods, using examples from daily practice in the clinical genetic laboratory. The use of SNPs (single nucleotide polymorphisms) to detect large deletions and duplications is discussed. One paragraph describes how single gene sequencing is used to detect small mutations (nucleotide changes, small deletions and/or insertions) in the BRCA1 and BRCA2 genes that are tested routinely in the laboratory and take up more than 20% of the tests performed. The diagnosis of patients with a repeat expansion as their causative mutation asks for a different approach. Finally, the diagnostics for patients with intellectual disability is described. In the past years these patients often had no diagnosis, but with the introduction of exome sequencing in clinical practice, up to 30% of these patients now have a definitive diagnosis.

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Erasmus MC: University Medical Center Rotterdam

van den Ouweland, A., Thornton, A., Knijnenburg, J., van Slegtenhorst, M., & Hoefsloot, L. (2017). Clinical genetics. In Molecular Diagnostics: Part 2: Clinical, Veterinary, Agrobotanical and Food Safety Applications (pp. 155–174). doi:10.1007/978-981-10-4511-0_8