Chapter 7: Genetic/Congenital Disorders

Polysomy

Presence of more than two chromosomes to a set, occurs when a germ cell containing more than 23 chromosomes is involved in conception

Prenatal Screening

Purpose of this is to detect fetal abnormalities but also to allow anxiety and provide assistance to prepare a child with a specific disability Can not be used to rule out disorders

Teratogenic Agent

A chemical, physical, or biologic agent that produces abnormalities during embryonic or fetal development

Codominance

A condition where both alleles of a gene pair are expressed fully in the heterozygote

Autosomal Dominant Disorders

A single mutant allele from an affected parents is transmitted to an offspring regardless of sex

Tay-Sachs Disease

A variant of a class of lysosomal storage diseases in which there is a failure to break down ganglion sides of cell membranes Most prominent in the brain neurons and retinas There is no cure

Chromosomal Disorders

Accounts for a large portion of reproductive wastage, congenital malformations, and chromosome disorders May take form in alterations of structure or an abnormal number of chromosomes

Single Gene Disorders

Caused by a defective or mutant allele at a single gene locus and follow patterns of inheritance All of these disorders lead to formation of an abnormal protein or decreased production of a gene product

Marfan Syndrome

An autosomal disorder of the connective tissue which gives shape and structure to other tissues in the body and holds them in place There is no cure Long thin body, very long extremities and long fingers

Chorionic Villus Sampling

An invasive procedure that can be used for fetal chromosome studies, DNA analysis, and biochemical studies Done after 10 weeks of gestational age

Variable Expressivity

Autosomal disorders can also be expressed differently among people

Multifactorial Inheritance Disorders

Caused by multiple genes and in many cases environmental factors Tend to involve a single organ or tissue derived from the same embryonic developmental field

Down Syndrome

Causes a combination of birth defects including some degree of intellectual disability, facial characteristics, and other health problems Most common chromosomal disorder Small head, flat face, open mouth, protruding tongue

Klinefelter Syndrome

Condition of testicular dysgenesis accompanied by the presence of one or more extra X chromosomes Fairly common to have the extra chromosome but the symptoms are uncommon Inability to produce normal amounts of testosterone, enlarged breasts, small testes, inability to produce sperm

Neurofibromatosis

Condition that causes tumors to develop from schwann cells of the neurological system Genetic defect in a tumor suppressor gene that regulates cell growth Lesions project from skin that are firm, round, and can be painful

Birth Defects

Congenital defects are abnormalities of a body structure, function, or metabolism that are present at birth Leading cause of infant death

Genetic Disorder

Described as a discrete event that affects gene expression in a group of cells related to each other by gene linkage Some are a result of an abnormal number of chromosomes

Turner Syndrome

Describes an absence of all or part of the X chromosome Most frequent occurring genetic disorder in women Diagnosis is often delayed until late childhood Girls do not menstruate and show no signs of secondary sex characteristics

Folic Acid Deficiency

Has been implicated in the development of neural tube defects A significant decrease in neural defects with woman who took folic acid long term by woman of reproductive age

Aneuploidy

Having an abnormal number of chromosomes Failure of chromosomes to split during oogenesis or spermatogenesis

Radiation

Heavy dosage of this causes changes to genetic materials Causes skeletal malformations, and MR No evidence that diagnostic levels

Amiocentesis

Invasive diagnostic procedure that involves the withdrawal of a sample of amniotic fluid from the uterus Useful in women who have a family history of an inherited disease Can be performed outpatient starting at 15 weeks

Centric Fusion

Involves two acrocentric chromosomes in which the centromere is near the end There is only 45 chromosomes but the genetic material that is lost is so small it often goes unnoticed

Autosomal Recessive Disorders

Manifested only when both members of the gene pair are affected Both parents may be carriers but are unaffected

Consanguineous Mating

Mating of two related people Increases the chance that two people who mate will be carriers of an autosomal recessive disorder

Ultrasonography

Noninvasive method that uses reflections of high frequency sound waves to visualize soft tissue structures Number of fetuses, size and position, and placental location

Cleft Lip/Palate

One of the most common birth defects resulting in abnormal facial appearance and defective speech The immediate problem is feeding

Phenylketonuria (PKU)

Rare autosomal recessive metabolic disorder that is a deficiency of the liver which allows toxic levels of amino acids to accumulate in blood and tissues Causes MR, delayed speech, and impaired neuro damage Infants treated with this are given a special diet

Fetal Alcohol Syndrome

Refers to a group of physical, behavioral, and cognitive fetal abnormalities that occur secondary to drinking alcohol while pregnant Not always apparent in newborn but more so as infant develops The amount of alcohol a pregnant woman can consume is unknown

Monosomy

Refers to the presence of only member of a chromosome pair

Fragile X Syndrome

Single gene disorder that causes intellectual disability Most common form and affects boys more often than girls Most Abundant in brain and testes; father passing the gene on to all his daughters but not to his sons

Sex Linked Disorders

These are almost always associated with the Female (X) chromosome and the inheritance pattern is mainly recessive An unaffected mother carries one normal and one mutant allele

Chemical and drugs

Top the list of chemical teratogens Drugs cross the placenta and exposes fetal development

Cytogenic Studies

Used for fetal karyotyping to determine the chromosomal makeup of the fetus Detect abnormalities of chromosome number and structure

Reduced Penetrance

When a person inherits a dominant mutant gene but fails to express it