Genetic Approaches to Study Rheumatic Diseases and its Implications in Clinical Practice.

Rare and complex rheumatic diseases (RDs) present with immense clinical variability inherent to all immunological diseases. In addition to systemic and organ-specific inflammation, patients may display features of immunodeficiency or allergy, and as such, they may represent major diagnostic and therapeutic challenges. The person's genetic architecture has been a well-established risk factor for RDs, albeit to variable degrees. Patients with early-onset diseases and/or positive family history have a strong genetic component, while patients with late-onset RDs demonstrate a more complex interplay of genetic and environmental risk factors. Overall, the genetic studies in RDs have been instrumental to our understanding of innate and adaptive immunity in human health and disease. The elucidation of the molecular causes underlying rare diseases has played a major role in the identification of genes that are critical in the regulation of inflammatory responses. In addition, studies of patients with rare disorders may help determine the mechanisms of more complex autoimmune diseases by identifying variants with small effect sizes in the same genes. In contrast, studies of common RDs are carried out in cohorts of patients with well-established phenotypes and ancestry-matched controls, and they aim to discover disease-related pathways that can inform the development of novel targeted therapies. Knowing the genetic cause of a disease has helped patients and families understand the disease progression and outcome. Here, we discuss the current understanding of genetic heritability and challenges in the diagnosis of RDs and how this field may develop in the future.