University:
Franklin University
Course:
BIO-406 | Genetics
Academic year:

2020
Views:

157

Pages:

34
Author:

6AstralAdventurer

   One of the fastest moving fields in medical science. A technique to determine the genotype or phenotype of an organism. It is often used to detect faulty or abnormal genes in an organism.    Prenatal screening Newborn screening Carrier screening      This can detect a disorder before a baby is born. An ultrasound test is used to determine if the fetus is at a high or low risk from a genetic disorder. Disorders are diagnosed by examining a small amount of fetal cells. This carries a small risk to the fetus. If diagnosed early in the pregnancy, there is still the possibility of abortion. Prenatal screening is sometimes seen as controversial.       Advanced Maternal Age Previous Child With a Chromosome Abnormality Family History of a Chromosome Abnormality Family History of a Single-Gene Disorder Family History of Congenital Structural Abnormalities Family History of Undiagnosed Learning Difficulty Non invasive MATERNAL SERUM SCREENING Triple test or combined test Ultrasound invasive Amniocentesis Chorionic villus sampling  Ultrasonography 12 weeks’ gestation nuchal translucency (NT) Major anomaly 18–20 structural abnormalities NT >3mm <3mm Amniocentesis echo combined Anomaly scan >95% echo Amniocentesis?  pappA:low in IUGR  βhCG:high in preeclampsia and IUGR FTS High risk<1/50 Intermediate risk Low risk>1/1100 Amniocentesis or CVS STS or NIPT AFP in second trimester     Inhibin A Esteriol: low level in SLOS, sulfatase deficiency and ichthyosis AFP: high and NTD risk : anomaly scan βhCG STS result <1/270 >1/270 amniocentesis No addotional screening   AFP is raised in both the amniotic fluid and maternal serum in NTD maternal serum AFP screening for NTDs is neither 100% sensitive nor 100% specific. around 75% of screened open spina bifida cases are detected. US scanning at around 18–20 weeks, this is usually sufficient to visualize and diagnose NTD     Raised maternal serum AFP concentration is not specific for open NTDs: Threatened miscarriage Twin pregnancy Fetal abnormality  chromosome abnormalities, and in particular Down syndrome, can be screened for in pregnancy by taking into account risk factors such as maternal age, the levels of biochemical markers in maternal serum:  α-Fetoprotein Unconjugated estriol Human chorionic gonadotrophin Inhibin-A  NT    Anomaly scan normal Structural marker Soft marker one two NIPT amniocentesis amniocentesis        Brachycephaly Echogenic bowel Flat facies Echogenic intracardiac focus Nasal bone hypoplasia Short femur, short humerus Mild hydronephrosis      Maternal age 35 years or older Fetal ultrasound finding of soft marker History of prior pregnancy with a trisomy detectable by cell free DNA Parental balanced translocation with increased risk of trisomy Cell free DNA screening can be used as a secondry screening test     Is not used clinically to screen of single gene disorders Does not screen for NTD( AFP should still be offered) Does not replace routine fetal anatomic ultrasonic screen NIPT is a screening test and should be confirmed in high risk situations NIPT with high detection rate can be recommended to every pregnant women regardless of age and past Medical history   Twin pregnancy: NT and combined  Triplet : only NT  First visit in second trimester(14w)  First visit in 17w     Newborns are tested for diseases and early diagnoses allows for immediate treatment. A blood sample is tested for genetic disorders. In most of the USA, newborn screening is mandatory, unless parents have a religious objection to it. Sometimes residual blood samples are used for genetic research, as long as the samples are kept anonymous.  Clinical Examination  Newborn Bloodspot Screening This methodology is indebted to Robert Guthrie, an American microbiologist, whose niece was diagnosed with PKU in 1958.     This involves testing prospective parents for diseases that they show no symptoms of, but may carry a recessive gene for. A blood sample or cheek cell sample is analysed to determine whether either parent carries a faulty gene. If both parents carry a specific faulty gene, the chance of the fetus receiving the gene from both parents is 25%, and the chance of being a carrier is 50%. If both parents carry a faulty gene, they may decide to have prenatal testing on the fetus.  Preimplantation screening: Screening embryos fertilised by IVF before they are implanted into the uterus.  Presymptomatic screening: Screening to predict adult-onset diseases such as Huntington’s disease.  Presymptomatic screening: Screening to estimate the risk of developing cancer or Alzheimer’s disease as an adult.  Forensic/Identity testing: Screening to eg. determine the father of an individual (paternity test).