Inherited disease and prenatal investigations

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On the other hand, cystic fibrosis and sickle-cell anaemia are autosomal recessive which means that the diseases require two mutated copies of the specific gene to be inherited by the offspring, one each from either parent, in order to have the disease. Persons who inherit only one copy of a recessive mutation are carriers for the disease trait. The genetic or chromosomal abnormalities in the foetus can be identified through prenatal investigations in pregnant women. Amniocentesis and chorionic villus sampling (CVS) are two standard prenatal tests commonly performed during the first and second trimester of pregnancy. Generally, amniocentesis is done at 15-18 weeks’ gestation and CVS at 10-12 weeks’ gestation (Olney et al., 2001). Both are invasive screening procedures which are associated with risks to the foetus. Amniocentesis consists of removal of a small quantity of the amniotic fluid with the help of a hollow needle inserted into the uterus through the abdominal wall while CVS involves biopsy of the placental cells (ScienceDaily, 2006). The foetal cells thus obtained are further analysed for genetic abnormalities. 2. Briefly explain what Maple syrup urine disease (MSUD) is. What characteristic smell is associated with MSUD? Describe briefly why keto-acids are present in MSUD. Maple syrup urine disease (MSUD), a branched-chain ketoaciduria, is a metabolism disorder caused by a gene defect (Haldeman-Englert, 2009). It is an autosomal recessive disease. Urine in this condition generally smells like maple syrup. As the primary defect in this disease lies in the genes related to the oxidative decarboxylation enzymes involved in the metabolism of the branched-chain amino acids such as leucine, isoleucine, and valine, there is an accumulation of the keto acids in the blood. The branched-chain keto acids (BCKA) accumulating in MSUD are ?-ketoisocaproic acid, ?-ketoisovaleric acid, and ?-keto-?-methylvaleric acid (Funchal et al., 2005). 3. Explain the terms: Maternal PKU Biopterin deficiency The term maternal phenylketonuria (PKU) refers to the teratogenic effects of PKU during pregnancy. It is a genetic condition in which the high levels of phenylalanine during pregnancy in women with PKU can increase the risk of mental retardation, low birth weight, and birth defects in the newborn (GDSP Medical Terminology Glossary, 2010). Biopterin deficiency or tetrahydrobiopterin (BH4) deficiency comprises of heterogeneous autosomal recessive disorders. BH4 is a the cofactor for phenylalanine-4-hydroxylase, tyrosine-3-hydroxylase, and tryptophan-5-hydroxylase. Hence, the deficiencies are characterised by an imbalance in phenylalanine homeostasis, brain biosynthesis of catecholamine and serotonin (Scheinfeld and Jones, 2010). Like PKU, BH4 deficiencies impair developmental function. Some of the variants of BH4 deficiencies may be detected with PKU screening tests. 4. What is aminiotic fluid, and what does it mean when it produces a high salt content? The amniotic fluid is a clear, watery fluid that is found in the amniotic cavity. It is made up of the fluid that filters out of the maternal blood through the amniotic epithelium into the amniotic cavity as well as foetal constituents including urine, and exudates from the skin, the umbilical cord, the lungs and the kidneys (Trofatter, Jr. 2008). The osmolality (which is a measure of the amount of