Enzymes are protein catalysts for chemical reactions; as catalysts, they speed up reactions without being used up in the process, so only small enzyme quantities are required to carry out a reaction. Someone homozygous for a nonfunctional mutation in the enzyme-encoding gene has little or no enzyme activity, so will manifest the abnormal phenotype. A heterozygote (heterozygous individual) has at least half of the normal enzyme activity level, due to the expression of the wild-type allele. This level is normally enough to enable normal function and thus prevent phenotypic expression. Pathophysiology
Tay–Sachs disease is caused by insufficient activity of the enzyme hexosaminidase A. Hexosaminidase A is a vital hydrolytic enzyme, found in the lysosomes, that breaks down sphingolipids. When hexosaminidase A is no longer functioning properly, the lipids accumulate in the brain and interfere with normal biological processes. Hexosaminidase A specifically breaks down fatty acid derivatives called gangliosides; these are made and biodegraded rapidly in early life as the brain develops. Patients with and carriers of Tay–Sachs can be identified by a simple blood test that measures hexosaminidase A activity.The hydrolysis of GM2-ganglioside requires three proteins. Two of them are subunits of hexosaminidase A; the third is a small glycolipid transport protein, the GM2 activator protein (GM2A), which acts as a substrate-specific cofactor for the enzyme. Deficiency in any one of these proteins leads to ganglioside storage, primarily in the lysosomes of neurons. Tay–Sachs disease (along with AB-variant GM2-gangliosidosis and Sandhoff disease) occurs because a mutation inherited from both parents deactivates or inhibits this process.
Tipranavir (TPV), or tipranavir disodium, is a nonpeptidic protease inhibitor (PI) manufactured by Boehringer Ingelheim under the trade name Aptivus  AP-tiv-əs. It is administered with ritonavir in combination therapy to treat HIV infection. Tipranavir has the ability to inhibit the replication of viruses that are resistant to other protease inhibitors and it recommended for patients who are resistant to other treatments. Resistance to tipranavir itself seems to require multiple mutations. Tipranavir was approved by the Food and Drug Administration (FDA) on June 22, 2005, and was approved for pediatric use on June 24, 2008.Tipranavir should only be taken in combination with ritonavir and other antiretroviral drugs, and is not approved for treatment-naïve patients. Like lopinavir and atazanavir, it is very potent and is effective in salvage therapy for patients with drug resistance. However, side effects of tipranavir may be more severe than those of other antiretrovirals. Some side effects include intracranial hemorrhage, hepatitis, hepatic decompensation, hyperglycemia and diabetes mellitus. The drug has also been shown to cause increases in total cholesterol and triglycerides.Aptivus labeling has a black box warning regarding hepatotoxicity and intracranial hemorrhage. References
External links
"Tipranavir". Drug Information Portal. U.S. National Library of Medicine.