Medical Genetics Competency Quiz

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Questions and Answers

What is the primary reason for understanding gene mutations in relation to human diseases?

To determine the genetic history of a family.

To confirm the presence of infectious diseases.

To assess environmental factors contributing to disease.

To gain insights into diagnosis, prognosis, and therapeutic targets. (correct)

Which of the following statements about the clinical case of the infant with respiratory infections is most accurate?

The infant's environment is solely responsible for the respiratory infections.

The infant must have received newborn screening.

The diagnosis of staphylococcus aureus pneumonia suggests possible underlying genetic issues. (correct)

Recurrent infections at such a young age are unrelated to genetic factors.

In the context of gene mutations and human disease, which class of mutations is most likely to affect the structure and function of body organs?

Translocation mutations affecting non-coding regions.

Frameshift mutations that alter the reading frame of the gene. (correct)

Missense mutations that result in a different amino acid.

Silent mutations that do not change amino acids.

What outcome is most likely if a child has a single gene mutation related to immune response?

Increased susceptibility to recurrent infections. Signup and view all the answers

Which aspect of gene mutation is essential for understanding pathology and pathophysiology?

How mutations affect genomic integrity and cell function. Signup and view all the answers

Which of the following may not represent a direct consequence of chromosomal alterations?

Infectious disease susceptibility. Signup and view all the answers

Why is newborn screening significant in identifying genetic disorders?

It allows for early detection of potential future health problems. Signup and view all the answers

What is a common feature of single gene mutations that might impact a child's health?

They can lead to conditions like cystic fibrosis or sickle cell anemia. Signup and view all the answers

What distinguishes complex multifactorial genetic disorders from monogenic disorders?

They involve a mixture of genetic, environmental, and age-related factors. Signup and view all the answers

Which statement best describes incomplete penetrance?

A percentage of individuals with a specific genotype display the disease phenotype. Signup and view all the answers

What is the relationship between penetrance and expressivity?

Expressivity refers to the severity and presentation of symptoms, while penetrance is about the presence of symptoms. Signup and view all the answers

What is likely to happen if point mutations occur in the open-reading frame of a gene?

They may result in different outcomes based on the nature of the substitution. Signup and view all the answers

Which of the following is NOT a characteristic of complex multifactorial genetic disorders?

They are primarily caused by a single allele mutation. Signup and view all the answers

What does a disease with 100% penetrance imply?

Every individual with the genotype will show the disease phenotype, but severity may vary. Signup and view all the answers

Which factors can contribute to variable expressivity of a genetic disorder?

Environmental influences, modifying genes, and age. Signup and view all the answers

What term is defined as the likelihood that a patient with a specific genotype will display the disease phenotype?

Penetrance Signup and view all the answers

What is the inheritance pattern of cystic fibrosis?

Autosomal recessive Signup and view all the answers

Where is the CFTR gene located in humans?

Chromosome 7 at q31.2 Signup and view all the answers

What is the carrier frequency for cystic fibrosis in individuals of European descent in the U.S.?

1/25 Signup and view all the answers

What percentage of CF mutations are accounted for by the 23 most common mutations in the CFTR gene in the U.S.?

99.9% Signup and view all the answers

What method is commonly used for newborn screening of cystic fibrosis?

Blood sample from heel prick Signup and view all the answers

Which of the following best describes compound heterozygosity in cystic fibrosis patients?

Carrying two different pathogenic variants in the CFTR gene Signup and view all the answers

Among which ethnic population is cystic fibrosis the least common in the U.S. according to prevalence rates?

Asian Americans Signup and view all the answers

What type of sample is used for prenatal testing of cystic fibrosis?

Amniotic fluid or chorionic villus sample Signup and view all the answers

What is the primary method by which cells eliminate mRNAs with premature stop codons?

Nonsense-mediated decay (NMD) Signup and view all the answers

Which process primarily leads to gene copy number variations (CNVs)?

Transposon and recombination mechanisms Signup and view all the answers

What is the consequence of truncated proteins competing with full-length proteins?

Dysfunctional protein assemblies Signup and view all the answers

Short tandem repeat expansions can occur in which of the following regions of a gene?

In untranslated regions and coding regions Signup and view all the answers

Which mechanism is NOT involved in creating short tandem repeat expansions?

Segmental duplications Signup and view all the answers

How many human diseases have been identified as being caused by nucleotide repeat expansions?

More than 40 Signup and view all the answers

What type of sequences can undergo expansion and deletions due to DNA replication errors?

Short repetitive sequences Signup and view all the answers

Indels primarily lead to premature stop codons that are often regarded as toxic due to which reason?

They can compete with normal full-length proteins. Signup and view all the answers

What is the main purpose of nonsense mediated decay (NMD) in cells?

To degrade mRNAs containing nonsense codons before toxic proteins are produced Signup and view all the answers

What happens to proteins resulting from mutations that create a nonsense codon?

They are degraded before translation due to NMD Signup and view all the answers

How do insertion and deletion (INDEL) mutations typically affect the protein coding sequence?

They usually cause a frame shift unless they are multiples of three Signup and view all the answers

Why are nonsense codons less likely to be found in alternative exons?

Evolution has not favored their preservation in these areas Signup and view all the answers

What is the likelihood of a premature stop codon occurring after an INDEL?

It occurs approximately once every three out of 64 codons Signup and view all the answers

What could be a result of an INDEL occurring in a protein-coding exon?

Generation of a truncated protein due to a new stop codon Signup and view all the answers

Which of the following processes is NOT associated with causing INDEL mutations?

Nonsense mediated decay Signup and view all the answers

What is a key characteristic of INDEL mutations in terms of coding sequence length?

They can range significantly in length from one to several hundred nucleotides Signup and view all the answers

Study Notes

Gene Mutations & Human Disease Overview

Various diseases are linked to gene mutations, influencing diagnosis, prognosis, and treatment options.

Clinical Context

Complex multifactorial genetic disorders, the most common class of genetic diseases, involve multiple genetic and environmental variables rather than monogenic mutations.
Familial risk factors arise from multiple genetic variants, each with low penetrance, meaning one variant alone does not cause disease.
Penetrance is the likelihood of a genotype expressing the disease phenotype, with 100% penetrance resulting in all carriers showing symptoms.
Variable expressivity refers to different symptom severities and ages of disease presentation among individuals with the same genotype.

Clinical Case Study

A six-month-old girl with recurrent respiratory infections was diagnosed with staphylococcus aureus pneumonia after not receiving newborn screening.

Single Gene Mutations

Point Mutations: Single base substitutions that may lead to toxic protein production or nonsense mutations that are usually degraded through nonsense mediated decay (NMD).
Insertion/Deletion (INDEL) Mutations: Cause frame shifts in protein coding sequences, likely resulting in premature stop codons.
Cells prevent toxic truncated proteins by degrading mRNA with premature stop codons via NMD.
Short Duplications, Inversions, and Translocations: Can result from evolutionarily preserved mechanisms, contributing to gene copy number variations (CNVs).
Short Tandem Repeat Expansions: Involve expansions of repeat sequences linked to over 40 human diseases due to DNA replication errors.

Chromosomal Alterations

Genetic diseases can occur from larger chromosomal changes, impacting gene structure and function.

Clinical Case Discussion: Cystic Fibrosis (CF)

CF is a common inherited single-gene disorder, inherited autosomal recessively, linked to mutations in the CFTR gene on chromosome 7 (q31.2).
Carrier frequency in U.S. population: approximately 1 in 25 for European descent; prevalence among newborns is roughly 1 in 2500 to 1 in 3500.
Less common in African American (1 in 17,000) and Asian American (1 in 31,000) populations.
Newborn screening for CF involves blood samples; prenatal testing uses amniotic fluid or chorionic villus sampling.
Over 2000 mutations identified in CFTR gene, but 23 common mutations account for 99.9% of cases in the U.S.
Many patients are compound heterozygotes, carrying two different pathogenic variants in the CFTR gene.

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Description

Test your understanding of core concepts in medical genetics, focusing on basic sciences and alterations in structure and function. This quiz is designed for learners aiming to grasp key learning objectives in genetics. Perfect for students or professionals in the field of medical genetics.