USB1 (U6 snRNA biogenesis phosphodiesterase 1) is a key nuclease primarily located within the nucleus and responsible for RNA processing. Its most well-defined function is to catalyze the hydrolysis of the 2',3'-cyclic phosphate at the 3' end of the U6 small nuclear RNA (snRNA), generating an essential 3'-hydroxyl group. This process is crucial for spliceosome assembly and pre-mRNA splicing. Mutations in the USB1 gene directly cause cartilaginous-hair hypoplasia, a rare autosomal recessive genetic disorder. Affected individuals present with short-limbed dwarfism, sparse hair, immunodeficiency, and bone marrow failure, revealing the critical roles of USB1 in skeletal development, cell cycle regulation, and immune system function. Therefore, USB1 is not only a core factor in RNA metabolism but also an important disease-associated protein.