Familial exudative vitreoretinopathy (FEVR, pronounced as fever) is a genetic disorder affecting the growth and development of blood vessels in the retina of the eye. This disease can lead to visual impairment and sometimes complete blindness in one or both eyes. FEVR is characterized by incomplete vascularization of the peripheral retina. This can lead to the growth of new blood vessels which are prone to leakage and hemorrhage and can cause retinal folds, tears, and detachments. Treatment involves laser photocoagulation of the avascular portions of the retina to reduce new blood vessel growth and risk of complications including leakage of retinal blood vessels and retinal detachments. Information
Pathophysiology
FEVR is caused by genetic defects involving the regulation of blood vessel growth in developing eyes. As a result, there is poor blood vessel growth to the periphery of the retina. The lack of blood supply to the peripheral retina triggers the release of molecules that stimulate blood vessel growth, such as vascular endothelial growth factor (VEGF). However, this new blood vessel growth, also known as neovascularization, can lead to further complications such as the leakage and hemorrhage of retinal blood vessels, retinal tears, and detachments.Genetics
There have been several gene mutations associated with FEVR. These genes code for proteins involved in the WNT signaling pathway, which is involved in the development of the human eye and regulation of blood vessel growth. Depending on the genes involved, FEVR can follow an autosomal dominant, autosomal recessive, or X-linked inheritance pattern. There is varying penetrance and expressivity depending on the genes involved.
Telotristat ethyl (USAN, brand name Xermelo) is a prodrug of telotristat, which is an inhibitor of tryptophan hydroxylase. It is formulated as telotristat etiprate — a hippurate salt of telotristat ethyl.On February 28, 2017, the U.S. Food and Drug Administration (FDA) approved telotristat ethyl in combination with somatostatin analog (SSA) therapy for the treatment of adults with diarrhea associated with carcinoid syndrome that SSA therapy alone has inadequately controlled. Telotristat ethyl was approved for use in the European Union in September 2017.The U.S. Food and Drug Administration (FDA) considers it to be a first-in-class medication. Pharmacology
Telotristat is an inhibitor of tryptophan hydroxylase, which mediates the rate-limiting step in serotonin biosynthesis. Adverse effects
Common adverse effects noted in clinical trials include nausea, headache, elevated liver enzymes, depression, accumulation of fluid causing swelling (peripheral edema), flatulence, decreased appetite, and fever. Constipation is also common, and may be serious or life-threatening (especially in overdose). Formulations
It is marketed by Lexicon Pharmaceuticals (as telotristat etiprate). 328 mg telotristat etiprate is equivalent to 250 mg telotristate ethyl. References
Further reading
Kulke MH, ODorisio T, Phan A, Bergsland E, Law L, Banks P,  et al. (October 2014). "Telotristat etiprate, a novel serotonin synthesis inhibitor, in patients with carcinoid syndrome and diarrhea not adequately controlled by octreotide". Endocrine-Related Cancer. 21 (5): 705–14. doi:10.1530/ERC-14-0173. PMC 4295770. PMID 25012985. External links
"Telotristat ethyl". Drug Information Portal. U.S. National Library of Medicine. "Telotristat etiprate". Drug Information Portal. U.S. National Library of Medicine.