Disease Causing Mutations in the pre-mRNA and Major and Minor Spliceosomes. (A) Mutations in the RNA transcript itself can lead to splicing alterations. Similar mutations are also possible in the sequences controlling splicing of the minor introns, although are not depicted here. (B) Similarly, mutations in core spliceosome machinery of both the major and minor spliceosome have been shown to lead to altered splicing networks. Both of these scenarios can manifest in a disease phenotype. Abbreviations: MDS, myelodysplastic syndromes; MOPD1, microcephalic osteodysplastic primordial dwarfism type 1; SRSF, serine/arginine-rich splicing factor.