Chapter 4 - Hereditary and Environmental Influences on Childbearing

What pertains to development results that direct cellular functions provided by genes that constitute the 46 chromosomes in every somatic cell?

Hereditary or genetic

How can disorders occur?

If too much or too little genetic material exists. OR more genes are abnormal and provide incorrect directions

What is the building block of genes and chromosomes?

DNA

What are the 3 units of the DNA?

(1) a sugar (Deoxyribose)

(2) a phosphate group

(3) one of four nitrogen bases (adenine, thymine, guanine and cytosine)

How do the nitrogen bases pair?

o Adenine pairs with thymine

o Guanine pairs with cytosine

What is a segment of DNA that direct ts the production of a specific product needed for body structures or function?

Gene

If an allele occurs at least 1% of the time in the population - it is called?

polymorphism

What are some changed genes, could be harmless but many are harmful?

Mutations

What are four things that mutations may cause (harm)?

Substituting incorrect bases for normal bases

Interrupting the normal gene sequence or stopping it prematurely

Duplicating some bases or entire gene sequence

Adding or subtracting some bases within those marking up a gene's sequence of bases, which will alter the amino acids it causes to be assemble

Mutations can occur in what types of cells?

Gametes (reproductive or germ cell)

Somatic (other body cells)

If a mutation occurs in a gamete, where does it come from?

Either the egg or sperm (inherited)

If a mutation occurs in a somatic, where does it come from?

occur in the cells as a malignancy, it is not transmitted generation to generation

What are 3 ways that genes are studied?

By measuring the products they direct cells to produce such as an enzyme or other substance

By directly studying the gene's DNA

By analyzing the gene's close association with another gene that can be studied in one of the previous two ways

What types of tissues do they use to study genes/chromosomes?

-Blood cells

-skin cells

-hair follicles

-fetal cells form amniotic fluid or chorionic villi

What can be used to determine or select certain embryos to be implanted in the uterus? What does this prevent?

Eight-Cell state (Blastomere)

prevents implantation of embryos with a specific gene defect or common chromosome defects

Alleles can be paired how?

Idenitical (homozygous)

Different (heterozygous)

What term is used to describe the way a person's genotype is translated into the phenotype?

Dominance

Genotype is ?

genetic composition

Phenotype is?

observable characteristics of an organism

If genes are located on the autosomes they are what?

dominant or recessive

If genes are located on the X chromosome they are what?

paired only in females

What are the benefits for greater knowledge about specific human genes?

o Performing genetic testing to determine the risk for a disorder or the actual or probable presence of the disorder

o Basing reproductive decisions on more accurate and specific information than has previously been available

o Identifying genetic susceptibility to a disorder so interventions to reduce risk can be instituted

o Using gene therapy to modify a defective gene

o Modifying therapy such as medication based on an individual's genetic code or the genetic makeup of tumor cells

o Individualizing treatment or medications for a specific person

What are the legal and ethical issues that arise about knowledge of genetic information?

o Genetic information has implications for others in the person's family, raising privacy issues.

o Knowledge about a genetic disorder often precedes knowledge about treatment of the disorder

o Identification of genetic problems could lead to poor self-esteem, guilt, and excessive caution or conversely a reckless lifestyle

o Pre-symptomatic identification of genetically influenced illness would be a source of long-term anxiety

o Genetic knowledge could affect one's choice of a partner

Cells for chromosome analysis must be living or dead cells?

living

What are the three major patterns of single gene inheritance?

autosomal dominant

autosomal recessive

X-Linked

Which gene pattern is produced by a dominant gene on a non-sex chromosome? Example

Autosomal dominant

Huntington's

What are some characteristics of Autosomal dominant?

50% chance of transmitting the disorder to each biologic child

Abnormal gene's expression may vary in severity.

May carry a dominant gene but have no apparent expression

Some having the abnormal gene will always have the disease.

New mutations can bring a trait into a family.

A person affected with autosomal dominant disorder is usually heterozygous

What occurs if a person receives copies of a recessive gene carried the autosome?

Autosomal recessive

What are some characteristics of Autosomal recessive?

Everyone is estimated at carry these types of genes, but the disorder will not manifest

Consanguinity (blood relationship) of the parents since relatives have more genes in common including the abnormal one

Groups isolated by culture, geography, religion or other factors

Some disorders are severe and affected persons may not live long enough to reproduce

Examples are phenylketonuria (PKU) (inability to metabolize phenylalanine that causes brain and nerve damage if untreated) and cystic fibrosis

Expressed if a person receives two copies of a recessive gene

Abnormality is not expressed if compensated with a normal gene.

Many recessive disorders are severe.

What are some x-linked characteristics?

X-linked recessive traits are more common than x-linked dominant traits

Males are the only ones to show full effects of an x-linked recessive disorder because their only x chromosome has the abnormal gene on it

Females can show the full disorder if: has a single X chromosome (Turner syndrome) or born to an affected father and a carrier mother

Recessive is more common than dominant.

Males are usually the only ones who show effects of abnormal X-linked recessive trait.

Females can show full disorder in uncommon circumstances.

Can be mild (color blindness) or severe (hemophilia).

What is the same thing as venogram?

pedigree

Chromosome abnormalities are either what? AKA single gene disorders

numerical or structural

What is numerical chromosome abnormalities?

addition or missing an entire chromosome(s)

What is structural chromosome abnormalities?

Deletion, addition, rearrangement or fragility of the chromosome material

What are the types of numerical chromosome abnormalities?

Trisomy

Monosomy

Polyploidy

What type of numerical chromosome abnormality exists when each body cell contains an extra copy of one chromosome bringing the total number to 47 instead of 46?

trisomy

What are examples of Trisomy numerical abnormality?

Down's syndrome (trisomy 21)

Klinefelter syndrome (Sex chromosome) - Males are taller than usual and have gynecomastia and are usually sterile

What type of numerical chromosome abnormality exists when each body cell has a missing chromosome with a total of 45?

Monosomy

What is an example of monosomy numerical chromosome?

Turner syndrome

only one where there is postnatal life. Has a single X chromosome and is always female. Large cystic masses on either side of the neck may be found on ultrasonography and lead to the diagnosis. She will be very short and will not have a menstrual period or develop secondary sex characteristics. Usually have normal intelligence but may have difficulty with spatial relationship or visual problems such as reading a map. Broad shield like chest with widely spaced nipples and kidneys may be joined which will require corrective surgery. Treatment with estrogen helps with development of secondary sexual characteristics and preventing osteoporosis. Turner syndrome - missing one X on pair 23 on the sex chromosome. Considered female but cannot get pregnant will not have menstrual cycles.

What type of numerical chromosome abnormality may occur when gametes do not halve their chromosome number during meiosis and retrain not members of each pair? OR when two sperm fertilize an ovum at the same time.

Polyploidy - # of chromosome is a multiple of 23 (69 or 92). Usually results in an early spontaneous abortion

What chromosome abnormality may involve the structure of one or more chromosomes. Some of these rearrangements are common harmless variations. Others are harmful because important genetic material is lost or duplicated in the structural abnormality?

Structural

What type of disorders occur because of a genetic predisposition combined with environmental factors?

Multifactorial Disorders

What is an example of multifactorial disorder?

two embryos may have equal genetic susceptibility for spina bifida; however the disorder will not occur if maternal intake of folic acid occurs

What are some of the most common birth defects encountered?

Heart defects

Neural tube defects (anencephaly (absence of most of the brain and skull), spina bifida and encephalocele

Cleft lip and cleft palate

Pyloric stenosis

The risk for occurrences reoccurrence of multifactorial disorders depends on what?

It is not fixed but varies according to the number of close relatives affected, severity of the defects in affected persons, genes of the affected person and geographic location?

What are agents in the fetal environment that either cause or increase the likelihood that a birth defect will occur?

teratogens

What are some teratogens?

Maternal infectious agents (viruses, Bacteria)

Drugs

Pollutants

Ionizing radiation

Maternal hyperthermia

Maternal medical disorders

What are factors that make it difficult to establish the teratogenic potential?

Retrospective Study - mothers cannot remember what substances they ingested or was exposed to during pregnancy

Timing of exposure - agents may be harmful at one stage of prenatal development but not at others

Different susceptibility of organ systems - some agents affect only one fetal organ, or they affect one system at one stage of development and another at a different stage of development

Uncontrolled fetal exposure - exposures cannot be controlled to eliminate extraneous agents. An agent can be toxic at one dose and may have no apparent effect at another

Placental transfer - agents vary in their ability to cross the placenta

Individual variations - fetuses show varying susceptibility to harmful agents

Non-transferability of animal studies - results of animal studies cannot always be applied to humans

Risk for damage from an uncontrolled maternal disorder - some maternal disorders like hypertension or epilepsy may cause fetal damage if not controlled

Box 4.3 Page 70

Box 4.3 page 70

What are some mechanical forces that interfere with normal prenatal development?

oligohydramnios

fibrous amniotic bands

What is abnormally small amount of amniotic fluid? Why is this harmful to the fetus?

oligohydramnios - it reduces the cushion and may case clubfoot and fetal lung development

What may result in tears in the inner sac and result in limb amputation?

fibrous amniotic bands

What is the purpose of genetic counseling?

to educate individuals or families with accurate information so they can make informed decisions about reproduction and appropriate care for affected members

Genetic Evaluation may include what factors?

Complete medical history

Medical history of other family members

Laboratory, imaging and other studies

Physical assessment of a child with the birth defect and other family members as needed

Examination of photographs especially deceased or unavailable

Construction of a genogram or pedigree

Box 4.4 Page 72

Box 4.4 Page 72

If a diagnosis is established, then genetic counseling educates the family about what?

What is known about the cause of the disorder

The natural course of the disorder

The likelihood the disorder will occur or recur in other family members

Current availability of prenatal diagnosis for the disorder

The ways a couple may be able to avoid having an affected child

Availability of treatment and services for the person with the disorder

What can be consumed before and during pregnancy to decrease the risk of neural tube defects? What amount?

Folic Acid 0.4mg daily

What are indications that Genetic Counseling may be needed?

o Maternal age 35 years of older

o Paternal age 40 years of older

o Members of a group with increased incidence of a specific disorder

o Carriers of autosomal recessive disorders

o Women who are carriers of x-linked disorders

o Couples related by blood (consanguineous)

o Family history of birth defect or intellectual disability

o Family history of unexplained stillbirth

o Women who experience multiple spontaneous abortions

o Pregnant women exposed to known or suspected teratogens or other harmful agents either before or during pregnancy

o Pregnant women with abnormal prenatal screening results such as multiple-marker screen or suspicious ultrasound findings

What are some examples of problems in genetic counseling and prenatal diagnosis?

o Inadequate medical records

o Uncertain gestational age or inadequate prenatal care

o Family members' refusal to shar information

o Records that are incomplete, vague or uninformative

o Inconclusive testing

o Too few family members available when family studies are needed

o Inadequate number of live fetal cells obtained during amniocentesis

o Failure of fetal cells to grow in culture if other testing techniques are not useful

o Ambiguous prenatal test results that are neither clearly normal nor clearly abnormal

o Unexpected results from prenatal diagnosis

o Finding an abnormality other than the one for which the person was tested

o Nonpaternity revealed with testing

o Inability to determine the severity of prenatally diagnosed disorder

o Inability to rule out all birth defects

o Patient misunderstanding of the mathematical risk as it is presented

What roles do nurses play in OB?

-Genetic counseling team

-Women's health nurses

-Antepartum nurses

-Intrapartum and neonatal nurses

-Pediatric nurses

How can nurses assist a woman who may benefit from genetic counseling?

o Identifying families for referral

o Helping the family decide about genetic counseling

o Teaching about lifestyle

o Providing emotional support

o Helping the family deal with abnormal results