While the relative occurrence of such introns is low, they nonetheless represent a possible source of pathogenic variants [95], with mutations affecting the U12 5′-splice sites of introns in the STK11 [96] and TRAPPC2 [97] genes being shown to cause Peutz–Jeghers syndrome and spondyloepiphyseal dysplasia tarda, respectively. Here, STK11 is linked to spondyloepiphyseal dysplasia tarda.