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Genetics. Denice Gardner, MSN, NNP-BC. Objectives. Discuss genetics and its affects on the newborn. Genetics. Pictures included in presentation were obtained from the Mosby’s Nursing Consult web site Graphics used in presentation were created by the author. Terminology.

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Genetics


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    1. Genetics Denice Gardner, MSN, NNP-BC

    2. Objectives • Discuss genetics and its affects on the newborn

    3. Genetics • Pictures included in presentation were obtained from the Mosby’s Nursing Consult web site • Graphics used in presentation were created by the author

    4. Terminology • Genetics- study of heredity • Chromosome- structural element in a cell that contains the genes and all the genetic information; human cells have 23 pairs of chromosomes • DNA- double-stranded nucleotide that carries genetic material • Gene- segments of the DNA that are responsible for inherited traits; contain the “blueprint for everything that will make “you”

    5. Terminology • Allele- variations in a gene; segregates during meiosis; receive only one pair from each parent; only 2 alleles can be present in one person • Autosome- one of the 22 chromosomes that do NOT determine the sex of a person • Sex chromosome- the X & Y chromosome that determines the sex of a person

    6. Terminology • Gamete- one of the 2 cells that joins together during sexual reproduction to create a new being • Genotype- genetic make-up of a person • Phenotype- biochemical, physiologic, & morphologic characteristics of a person (hair color, skin type, etc.) & is determined by his/her genotype and environment

    7. Terminology • Haploid- number of chromosomes in a gamete; half the number of chromosomes in a person, 23 chromosomes • Diploid- contains a set of maternal & paternal chromosomes to equal 46 total chromosomes • Locus- location of the gene in the chromosome • Penetrance- degree to which an inherited trait will be expressed in a person

    8. Dominant & Recessive Genes • Dominant- expressed & transmitted even if only ONE parent has the gene • Recessive- expressed only when BOTH parents have the gene • Homozygous- two identical alleles for a particular gene (one from each parent) • Heterozygous- two different alleles for a particular gene

    9. Possible Combinations • Both can be dominant (AA) • Both can be recessive (aa) • One can be dominant & one can be recessive (Aa)

    10. Autosomal Dominant • Appears in every generation without skipping • Either parent can pass the gene on to their children • Risk for affected individuals to have affected children is 50% with every pregnancy • If 2 affected parents mate, 75% of their children will be affected • Unaffected individuals do NOT have affected children • Trait is found equally in males and females

    11. Autosomal Dominant

    12. Autosomal Recessive • Expressed only when both parents transmits it to their offspring • Alternates generations • If 2 affected people mate, all children with be affected • If 2 carriers mate, the risk of having an affected offspring is 25% • If a carrier & an affected person mate, the risk of having an affected offspring is 50% • Risk of an unaffected carrier having a child who is a carrier is 50% with each pregnancy

    13. Autosomal Recessive

    14. X-Linked Dominant • Female children of affected males are ALL affected • Male children of affected males are unaffected • Trait appears in every generation • All children of affected females MAY be affected • X-Linked dominant problems affect twice as many females as males

    15. X-Linked Dominant

    16. X-Linked Recessive • Only Male children are affected. (Female may be affected if mother is a carrier and father is affected) • Traits cannot be transmitted from father to son because the father only contributes the Y chromosome • Transmission of the trait occurs from father to all daughters (who will be carriers)

    17. X-Linked Recessive • Heterozygous females transmit the gene to half of their sons, who will be affected, & to half their daughters, who will be carriers • Transmission is horizontal among males of the same generation & then skips a generation • Carrier females transmit the disorder

    18. X-Linked Recessive

    19. Chromosomal Defects: Abnormal Number • Polyploidy- contains more than 2 sets of chromosomes, showing multiples of the haploid number; usually dies as embryos or fetuses • Nonmultiples- designated by the suffix “-somy” • Monosomy- one less than the diploid number (45 chromosomes) • Trisomy- one more than the haploid number (47 chromosomes)

    20. Chromosome Defects: Abnormal Number • Causes- • Nondisjunction- failure of paired chromosomes to separate during cell division; most common cause of all chromosome disorders • Chromosome lag- failure of a chromosome to travel to the correct daughter cell • Anaphase lag- failure of a chromosome or chromatin to be incorporated into one of the daughter nuclei following cell division as a result of delayed movement during anaphase

    21. Mosaicism: Chromosomal Defects: Abnormal Number • Mosaicism: • Nondisjunction of an anaphase lag that occurs during cell division after fertilization • Cells within the same person that have different genetic make-up

    22. Chromosomal Defects: Abnormal Structure • Deletion- loss of part of a chromosome • Translocations- displacement of part of a chromosome to an abnormal site, whether on another chromosome or in the wrong position on the same chromosome • Polygenic effects- type of inheritance in which a trait is dependent on many different gene pairs with cumulative effects

    23. Chromosome Defects: Abnormal Structure • Environmental influences- nutrition, drugs, & living environment (radiation, pollution, bacteria, virus) that affect the genetic make-up & developing embryo while in utero • Duplication- duplication of an area of the DNA that contain contains a gene; results in mutations that have no deleterious affects on a person

    24. Chromosomal Defects: Abnormal Structure • Inversion- area of a chromosome breaks off and then reattaches itself in the opposite direction • Nonreciprocal translocation- one-way transfer of genes from one chromosome to another

    25. Chromosomal Defects: Abnormal Structure • Basic Generalizations • Loss of an entire chromosome is usually incompatible with life • One X chromosome is necessary for life & development • If the Y-chromosome is missing, life & development may continue but will follow female pathways

    26. Chromosomal Defects: Abnormal Structure • Extra entire chromosomes, translocations of extra chromatin material, & insertion of extra chromatin material are often compatible with life & development • Multiple congenital structural defects are present when gross aberrations are present

    27. Prenatal Testing • Alpha-Fetoprotein Test (AFP) • Usually done at 16-18 weeks gestation • Is a screening test, not a diagnostic test • If abnormal, ultrasound should be obtained

    28. Prenatal Testing • Elevated AFP may indicate • Greater gestational age than expected • Multiple gestation • Risk of neonatal complications, including spontaneous abortion, PTL, or IUGR • Fetal structural defects: neural tube, abdominal wall, esophageal or intestinal obstruction, or renal anomalies

    29. Prenatal Testing • Multiple Marker Screen (“Quad Screen”) • Measures AFP, hCG, unconjugated estriol (uE3), & dimeric inhibin-A (DIA) • Useful in detecting conditions like trisomies • Usually done between 15-20 weeks gestation • If, abnormal, ultrasound should be obtained

    30. Prenatal Testing • Ultrasonography- uses high-frequency sound waves to display sectional planes of the uterine contents on a monitor • Recommended by 16-20 weeks of age for gestational age verification & assessment • Used to detect abnormalities of the fetus, placenta, amniotic fluid, & uterus & to monitor changes in anatomy & growth with serial ultrasounds • Only as good as the person’s training-not just on the equipment

    31. Prenatal Testing • Amniocentesis- removal of amniotic fluid through a needle placed through the abdomen, usually in conjunction with ultrasonography, for the purpose of chromosome analysis & other biochemical tests • Usually done between 16-18 weeks gestation • Indications for procedure: • Advanced maternal age (>35yrs at time of delivery) • Previous fetus with a neural tube

    32. Prenatal Testing • More indications for procedure • Both parents known heterozygous carriers of autosomal recessive chromosome • Both parents known carriers of sex-linked recessive disorder • Patient or partner with balanced chromosomal translocation of his or her chromosomes • High or low AFP with accurate gestational age • Previous fetus with Down’s Syndrome

    33. Prenatal Testing • Chorionic Villi Sampling- insertion of a needle through either the cervical os or through the abdomen, in conjunction with ultrasound, to obtain a sample of fetal tissue from the growing placenta for chromosomal analysis & other biochemical tests • Usually done at 8-10 weeks • Indications: • Patient prefers to make decision regarding pregnancy in the 1st trimester • Severe oligohydramnios

    34. Prenatal Testing • Complications: • Multiple gestation • Uterine bleeding during this pregnancy • Active genital herpes or other cervical infection • Uterine fibroids • Takes 24-48 hours for initial results

    35. Prenatal Testing • Percutaneous Umbilical Cord Sampling-removal of blood through a needle inserted through the abdomen and into the umbilical vein, in conjunction with ultrasound • Performed from 18 weeks until term • Indications: • Patient wants fast results to support decision regarding pregnancy • Abnormality is identified late in pregnancy

    36. Prenatal Testing • More indications: • Patient has been exposed to infectious disease that could affect development of fetus • Blood incompatibility (Rh disease) • Drug or chemical level is fetal blood needs to be assessed • Fetal blood analysis 3 days

    37. Postnatal Testing • Chromosome analysis/karyotype- photograph of the chromosomal make-up of an individual, including the number of chromosomes & any abnormalities • Polymerase Chain Reaction (PCR)- technique to copy small segments of DNA for analysis; useful in disorders with recurring mutations • High-resolution banding/prometaphase banding- useful for identification of subtle chromosomes

    38. Postnatal Testing • Microarray- assesses the ability of mRNA molecules to and interact with DNA molecules; assesses gene expression within a single sample or in comparison to 2 different cell types or tissue samples; need only a small sample of blood or tissue; can be done on healthy or diseased tissue

    39. Postnatal Testing • Fluorescence in situ hybridization (FISH)- cytogenic technique that can be used to detect and localize the presence or absence of specific DNA sequences on chromosomes; uses fluorescent probes that bind to only those parts of the chromosome with which they show a high degree of sequence similarity

    40. Genetic Counseling • Goal- to assist the family in understanding • Diagnosis • Role of heredity • Recurrence risks & options • Possible courses of actions • Methods of ongoing adjustment

    41. Genetic Counseling • Indications • Previously affected child, parent, or grandparent • Congenital malformation • Sensory defect • Metabolic disorder • Mental retardation • Known or suspected chromosome abnormality • Neuromuscular disorder • Degenerative CNS disease

    42. Genetic Counseling • More indications • Previously affected cousins • Muscular dystrophy • Hemophilia • Hydrocephalus • Consanguinity • Hazards of ionizing radiation • Recurrent miscarriages • Concern for teratogenic effect • Advanced maternal age • High or low AFP

    43. Newborn Care: Terminology • Birth defect- structural or functional abnormality of the body that is present from birth • Syndrome- group of anomalies that cannot otherwise be explained & occurs in similar patterns of expressions (ex. Fetal alcohol syndrome) • Sequence- primary anomaly that sets a pattern for other anomalies (Ex. Pierre Robin)

    44. Newborn Care: Terminology • Association- nonrandom occurrence of multiple anomalies in 2 or more people (ex. CHARGE) • Malformation- abnormality of morphogenesis due to intrinsic problems within the developing structures (ex. Neural tube defect) • Deformation- abnormality of morphogenesis due to intrinsic problems within the developing structures (ex. uterine position defects)

    45. Newborn Care: Terminology • Disruption- abnormality of morphogenesis due to disruptive forces or pressure acting on the developing structures (ex. Amniotic bands) • Genetic heterogeneity- different causes may produce different characteristics (ex. Hydrocephalus, cleft lip & palate)

    46. Newborn Care • History • Family • History of 3 generations • Defects in the family history related to the problem with the child • History of consanguinity • Reproductive history (frequent miscarriages???) • Pattern of inheritance of the problem

    47. Newborn Care • Prenatal • Length of gestation • Fetal activity level • Maternal exposure: infection, illness, high fever, meds, alcohol, smoking, X-rays, known teratogens, illicit or prescription drug use • Obstetric factors: uterine malformations, labor complications, presenting fetal part • Neonatal factors: birth weight, length, HC, Apgar score

    48. Newborn Care: Assessment • Physical Exam • General: asymmetry, inappropriate size & length • Face: configuration; centered features with normal spacing; round, triangular, birdlike, elfin, or expressionless characteristics • Head: size of anterior fontanelle, prominence of frontal bone, flattened or prominent occiput, abnormalities in shape (large or small)

    49. Newborn Care: Assessment • Skin: intact, presence of skin tags, open sinuses, tracts, etc. • Hair: texture, presence of whorls • Eyes: structure, color of iris, presence of colobomas, centering & spacing of epicanthal folds, ptosis, slanting, eyelash length • Ears: protruding or prominent shape, location, low set, unilateral or bilateral defect, presence &/or degree of rotation