Immunodeficiency Disorders: Molecular Genetics, Clinical Phenotypes, and Gene-Based Therapies

This chapter provides a detailed review of primary immunodeficiency diseases (PIDs), encompassing monogenic disorders of innate and adaptive immunity, newly described inborn errors of immunity identified through next-generation sequencing, and the expanding phenotypic spectrum associated with immune regulatory defects. It critically evaluates the genotype-phenotype relationships that define clinical presentation, infectious susceptibility, and immune dysregulation in major immunodeficiency categories, integrating recent registry-level and translational data. The chapter further discusses advances in gene therapy, hematopoietic stem cell transplantation, and precision pharmacological approaches that are transforming the therapeutic landscape for patients with PIDs.