40 Questions
What is an example of a familial predisposition to a disease?
Familial breast or colon cancer
What type of disorders are characterized by a single gene affecting multiple organ systems?
Single gene disorders
What is the main purpose of collecting family history information?
To establish biological relationships and clarify medical conditions
How many generations of family history information should be collected?
3 generations
What type of disorders have a dominant or recessive pedigree pattern?
Single gene disorders
What is the approximate percentage of liveborns affected by chromosomal disorders?
0.6%
What type of disorders involve multiple organ systems and can be inherited or occur de novo?
Chromosomal disorders
What is the main difference between single gene and multifactorial disorders?
Single gene disorders have a single genetic cause
What symbol is commonly used to represent a pregnancy that did not result in a live birth?
X
In a pedigree, what type of line is used to connect a parent to their offspring?
Vertical line
What is the term for a relationship between two people who are related by blood or adoption?
Consanguineous relationship
What is the term for a person whose sex is unknown or ambiguous?
P
What should a genetic counselor ask to identify affected relatives in a family?
Have you or your partner had any miscarriages?
What can be a red flag for a genetic disorder in a family?
All of the above
What is the term for a person who carries a genetic mutation but does not exhibit the condition?
Carrier
What is the purpose of constructing a genetic family tree?
To identify risk factors for genetic conditions
What is the typical inheritance pattern of autosomal dominant disorders?
One mutated copy of the gene in each cell is sufficient to cause the disorder
What is the name of the online database that collects and updates information on monogenic diseases?
Mendelian Inheritance in Man (OMIM)
Which of the following is an example of an autosomal dominant disorder?
Familial hypercholesterolemia
What is the name of the gene responsible for almost all cases of achondroplasia?
FGFR3
Which of the following is a characteristic symptom of achondroplasia?
Macrocephaly
What is the typical mode of inheritance of achondroplasia?
Autosomal dominant
What is the name of the type of genetic disorder that is caused by a mutation in a single gene?
Monogenic disorder
What is the term for the study of the transmission of traits from one generation to the next?
Mendelian genetics
What is the main difference between clinical and molecular classification of human diseases?
The clinical classification is based on phenotypic criteria, while the molecular classification is based on medical exploration.
What type of genetic disorders are caused by a single mutation in one gene?
Monogenic disorders
What is the purpose of ICD-11 in the context of disease classification?
To provide a standard diagnostic tool for clinical purposes
What is the characteristic of diseases that are classified as exogenous?
They are caused by an external agent, such as a chemical agent or virus
What is the main difference between somatic and germinal cells in the context of genetic disorders?
Somatic cells are affected in cancer, while germinal cells are affected in genetic disorders
What is the characteristic of multifactorial diseases?
They are caused by a combination of small variations in genes that may predispose to a serious health problem
What is the purpose of pedigrees in the context of genetic disorders?
To identify patterns of inheritance in families
What is the main difference between nuclear and mitochondrial genetic disorders?
Nuclear genetic disorders are caused by an error in the DNA sequence, while mitochondrial genetic disorders are caused by an excess or deficiency of the genes contained in the chromosomes
What is the typical outcome of deletions larger than 2% of the haploid genome?
They are usually incompatible with life
What is the characteristic feature of a ring chromosome?
A break occurs on each arm of a chromosome
What is the correlation between maternal age and the frequency of trisomy 21?
The frequency of trisomy 21 increases with increasing maternal age
What is the characteristic facial feature of Down syndrome?
Flat nasal bridge
What is the intelligence quotient range for individuals with Down syndrome?
IQ 30-60
What is the genetic mechanism underlying 4% of Down syndrome cases?
Robertsonian translocation between chromosome 21q and another acrocentric chromosome
What is the characteristic feature of the hands in Trisomy 18?
Hands closed with the second finger superimposed on the third and fifth on the fourth fist
What is the life expectancy of individuals with Trisomy 18?
Months
Study Notes
Familial Predisposition to Cancer
- Example: familial predisposition to breast or colon cancer
- Prevalence of disorders:
- Multifactorial (common): environmental influences act on a genetic predisposition to produce a liability to a disease
- Single gene (1% of liveborn): dominant/recessive pedigree patterns, affecting structural proteins, enzymes, receptors, and transcription factors
- Chromosomal (0.6% of liveborn): thousands of genes may be involved, affecting multiple organ systems at multiple stages in gestation
Pedigrees
- Why collect family history information?
- Patient concern
- Clinical feature
- Routine assessment
- Result of screening test
- Opportunistic
- What information to collect:
- Establish biological relationships
- Clarify medical conditions
- 3 generations
- Full name
- Date of birth (or age)
- Date of death (or age died)
- Medical information (age at diagnosis)
Classification of Human Diseases
- Clinical classification: based on International Classification of Diseases (ICD-11) published by the World Health Organization
- Molecular classification:
- Exogenous: due to external agents (chemical, drug, parasite, bacteria, virus, nutritional diseases, prion diseases)
- Genetic:
- Somatic (cancer)
- Germinal
- Monogenic (single mutation in one gene)
- Chromosomal (excess or deficiency of genes in chromosomes)
- Multifactorial: combination of small variations in genes that predispose to serious health problems
Monogenic Diseases
- Collected and updated in the online version of "Mendelian Inheritance in Man" (OMIM)
- Five models of monogenic disease:
- Autosomal dominant
- Autosomal recessive
- X-linked dominant
- X-linked recessive
- Y-linked
Autosomal Dominant Disorders
- One mutated copy of the gene in each cell is sufficient for a person to be affected
- Examples: familial hypercholesterolemia, myotonic dystrophy, neurofibromatosis I, Huntington disease, achondroplasia
Case Study: Achondroplasia
- Form of short-limbed dwarfism
- Patients have average-size trunk, short arms and legs, and macrocephaly
- Other symptoms: apnea, obesity, and recurrent ear infections
- Two specific mutations in the FGFR3 gene are responsible for almost all cases of achondroplasia
Drawing a Family Tree
- Steps in taking and recording a genetic family tree:
- Ask about informant and partner(s) and their children
- Be sensitive when trying to determine if partners are related by blood (consanguineous relationship)
- Record parents, siblings, and other relatives
Chromosomal Abnormalities
- Rings: formed when a break occurs on each arm of a chromosome, leaving two sticky ends that reunite as a ring
- Trisomy 21: Down syndrome
- Frequency of occurrence correlated with maternal age
- Phenotype: hypotonicity, characteristic facial features, short stature, mental retardation, congenital heart disease
- Genetic level: 95% have trisomy 21, 4% have a "Robertsonian translocation"
- Trisomy 18: Edwards syndrome
- Frequency of occurrence: 1/7500
- Phenotype: hypertonia, cardiac malformations, characteristic hand and foot features, mental retardation, poor postnatal survival
- Trisomy 13: Patau syndrome
- Frequency of occurrence: between 1/20000 and 1/25000
- Phenotype: hypertonia, cardiac malformations, characteristic facial features, mental retardation, poor postnatal survival
Learn about the different patterns of inheritance, including multifactorial, single gene, and chromosomal inheritance, and their relation to cancer, such as breast or colon cancer.
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