Genetics and Cancer: Inheritance Patterns

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Questions and Answers

What is an example of a familial predisposition to a disease?

A multifactorial disorder

A chromosomal abnormality

Familial breast or colon cancer (correct)

A single gene mutation

What type of disorders are characterized by a single gene affecting multiple organ systems?

Single gene disorders (correct)

Environmental disorders

Multifactorial disorders

Chromosomal disorders

What is the main purpose of collecting family history information?

To identify environmental risk factors

To establish biological relationships and clarify medical conditions (correct)

To diagnose a disease

To predict the risk of a disease

How many generations of family history information should be collected?

3 generations Signup and view all the answers

What type of disorders have a dominant or recessive pedigree pattern?

Single gene disorders Signup and view all the answers

What is the approximate percentage of liveborns affected by chromosomal disorders?

0.6% Signup and view all the answers

What type of disorders involve multiple organ systems and can be inherited or occur de novo?

Chromosomal disorders Signup and view all the answers

What is the main difference between single gene and multifactorial disorders?

Single gene disorders have a single genetic cause Signup and view all the answers

What symbol is commonly used to represent a pregnancy that did not result in a live birth?

X Signup and view all the answers

In a pedigree, what type of line is used to connect a parent to their offspring?

Vertical line Signup and view all the answers

What is the term for a relationship between two people who are related by blood or adoption?

Consanguineous relationship Signup and view all the answers

What is the term for a person whose sex is unknown or ambiguous?

P Signup and view all the answers

What should a genetic counselor ask to identify affected relatives in a family?

Have you or your partner had any miscarriages? Signup and view all the answers

What can be a red flag for a genetic disorder in a family?

All of the above Signup and view all the answers

What is the term for a person who carries a genetic mutation but does not exhibit the condition?

Carrier Signup and view all the answers

What is the purpose of constructing a genetic family tree?

To identify risk factors for genetic conditions Signup and view all the answers

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 Signup and view all the answers

What is the name of the online database that collects and updates information on monogenic diseases?

Mendelian Inheritance in Man (OMIM) Signup and view all the answers

Which of the following is an example of an autosomal dominant disorder?

Familial hypercholesterolemia Signup and view all the answers

What is the name of the gene responsible for almost all cases of achondroplasia?

FGFR3 Signup and view all the answers

Which of the following is a characteristic symptom of achondroplasia?

Macrocephaly Signup and view all the answers

What is the typical mode of inheritance of achondroplasia?

Autosomal dominant Signup and view all the answers

What is the name of the type of genetic disorder that is caused by a mutation in a single gene?

Monogenic disorder Signup and view all the answers

What is the term for the study of the transmission of traits from one generation to the next?

Mendelian genetics Signup and view all the answers

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. Signup and view all the answers

What type of genetic disorders are caused by a single mutation in one gene?

Monogenic disorders Signup and view all the answers

What is the purpose of ICD-11 in the context of disease classification?

To provide a standard diagnostic tool for clinical purposes Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

What is the purpose of pedigrees in the context of genetic disorders?

To identify patterns of inheritance in families Signup and view all the answers

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 Signup and view all the answers

What is the typical outcome of deletions larger than 2% of the haploid genome?

They are usually incompatible with life Signup and view all the answers

What is the characteristic feature of a ring chromosome?

A break occurs on each arm of a chromosome Signup and view all the answers

What is the correlation between maternal age and the frequency of trisomy 21?

The frequency of trisomy 21 increases with increasing maternal age Signup and view all the answers

What is the characteristic facial feature of Down syndrome?

Flat nasal bridge Signup and view all the answers

What is the intelligence quotient range for individuals with Down syndrome?

IQ 30-60 Signup and view all the answers

What is the genetic mechanism underlying 4% of Down syndrome cases?

Robertsonian translocation between chromosome 21q and another acrocentric chromosome Signup and view all the answers

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 Signup and view all the answers

What is the life expectancy of individuals with Trisomy 18?

Months Signup and view all the answers

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

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Description

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.