The shortest known introns belong to the heterotrich ciliates, such as Stentor coeruleus, in which most (> 95%) introns are 15 or 16 bp long. Classification
Splicing of all intron-containing RNA molecules is superficially similar, as described above. However, different types of introns were identified through the examination of intron structure by DNA sequence analysis, together with genetic and biochemical analysis of RNA splicing reactions.At least four distinct classes of introns have been identified:

Introns in nuclear protein-coding genes that are removed by spliceosomes (spliceosomal introns)
Introns in nuclear and archaeal transfer RNA genes that are removed by proteins (tRNA introns)
Self-splicing group I introns that are removed by RNA catalysis
Self-splicing group II introns that are removed by RNA catalysisGroup III introns are proposed to be a fifth family, but little is known about the biochemical apparatus that mediates their splicing. They appear to be related to group II introns, and possibly to spliceosomal introns. Spliceosomal introns
Nuclear pre-mRNA introns (spliceosomal introns) are characterized by specific intron sequences located at the boundaries between introns and exons. These sequences are recognized by spliceosomal RNA molecules when the splicing reactions are initiated. In addition, they contain a branch point, a particular nucleotide sequence near the 3 end of the intron that becomes covalently linked to the 5 end of the intron during the splicing process, generating a branched (lariat) intron. Apart from these three short conserved elements, nuclear pre-mRNA intron sequences are highly variable. Nuclear pre-mRNA introns are often much longer than their surrounding exons.
Medical uses
Asthma
Budesonide is given by metered-dose inhaler or nebulizer for maintenance and prophylactic treatment of asthma, including patients who require oral corticosteroids and those who may benefit from a systemic dose reduction. Inflammatory bowel disease
Formulations of delayed-release budesonide are an effective treatment for mild-to-moderately active Crohns disease involving the ileum and/or ascending colon. A Cochrane review found evidence for up to three months (but not longer) of maintenance of remission in Crohns disease.Budesonide assists in the induction of remission in people with active ulcerative colitis.Budesonide is highly effective and recommended as the drug of choice in microscopic colitis, for induction and maintenance of remission, and for both the lymphocytic colitis and collagenous colitis forms. Allergic rhinitis
Budesonide in the form of nasal sprays is a treatment for allergic rhinitis. Eosinophilic esophagitis
Topical budesonide has considerable effects in eosinophilic esophagitis. For this use, it is formulated as a tablet that disperses in the mouth, and sold under the trade name Jorveza. Bergers disease
Budesonide (Tarpeyo) is indicated to reduce proteinuria (increased protein levels in the urine) in adults with primary immunoglobulin A (IgA) nephropathy (Bergers disease) at risk of rapid disease progression. Side effects
Nasal budesonide inhalers have been associated with a number of side effects. These include nose irritation or burning, bleeding or sores in the nose, lightheadedness, upset stomach, cough, hoarseness, dry mouth, rash, sore throat, bad taste in mouth, change in mucus, and blurred vision.