Advancements in genetic sequencing technologies have brought about a new era in rare disease biology, facilitating the identification of an increasing number of such conditions. Scientists and patient advocates have begun tackling rare diseases with patient populations as low as one to two patients. Drug development for such diseases requires a personalized approach, often involving N = 1 clinical trials, which need to customize and alter study designs and statistical techniques commonly employed in standard population-based clinical trials. N = 1 trials focus on a single patient, posing challenges to extrapolating the results to a broader population. The limited patient size associated with rare diseases often results in reduced interest from pharmaceutical companies and academic researchers in pursuing such clinical trials. This often results in families of patients with rare diseases to take responsibility of designing and adapting the trial to one subject. In this chapter, we discuss drug development pipelines for rare diseases, with an emphasis on a case study involving a family engaged with developing a drug for their son with a rare genetic disorder.