Autosomal Dominant Disorders
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Questions and Answers

What is the characteristic of Treacher-Collins syndrome regarding the mandible?

  • Large mandible
  • Absent mandible
  • Small mandible (correct)
  • Deformed mandible

    • What is the reason for incomplete penetrance of a disease?

  • Interaction with the wild-type allele only
  • Interaction with other loci and the environment
  • Just chance alone
  • All of the above (correct)

    • How are penetrance rates estimated?

  • By conducting laboratory experiments
  • By examining a large number of families (correct)
  • By studying the genetics of a single individual
  • By examining a small number of families

    • What is variable expression?

    <p>The varying severity of a disease in different individuals</p> Signup and view all the answers

    What is the characteristic of Treacher-Collins syndrome regarding the lower eyelid?

    <p>Defect of the lower eyelid</p> Signup and view all the answers

    What is the type of inheritance that can exhibit incomplete penetrance?

    <p>Both autosomal dominant and autosomal recessive inheritance</p> Signup and view all the answers

    What is a characteristic of autosomal dominant disorders in terms of their manifestation in different individuals?

    <p>Variable expressivity</p> Signup and view all the answers

    In an autosomal dominant disorder, what is the probability of an affected individual transmitting the disease to each of their offspring?

    <p>One half</p> Signup and view all the answers

    What is an example of an autosomal dominant disorder?

    <p>Huntington disease</p> Signup and view all the answers

    What is a characteristic of autosomal dominant traits or diseases in a pedigree?

    <p>They are found in every generation</p> Signup and view all the answers

    What is incomplete penetrance?

    <p>When an individual has the genotype for a disease but does not exhibit the disease phenotype</p> Signup and view all the answers

    What is a possible reason for variability in autosomal dominant inheritance?

    <p>Variable expressivity</p> Signup and view all the answers

    What is the main reason for anticipation in some dominant conditions?

    <p>Unstable expanding nucleotide repeats</p> Signup and view all the answers

    What is the term for when an individual has two or more genetically different cell lines derived from a single zygote?

    <p>Mosaicism</p> Signup and view all the answers

    Why may there be no affected parent in a pedigree?

    <p>Because the condition is caused by a new mutation</p> Signup and view all the answers

    What type of mosaicism can lead to misclassification of a pedigree as having a recessive disease?

    <p>Germ-line mosaicism</p> Signup and view all the answers

    What is the term for the tendency of some dominant conditions to become more severe or have earlier onset in successive generations?

    <p>Anticipation</p> Signup and view all the answers

    What is the typical age of onset for Huntington's disease?

    <p>Around 40 years</p> Signup and view all the answers

    What is an example of a disease caused by an unstable expanding nucleotide repeat?

    <p>Huntington disease</p> Signup and view all the answers

    What is a possible cause of incomplete penetrance?

    <p>All of the above</p> Signup and view all the answers

    What is the primary reason for paternal anticipation in Huntington's disease?

    <p>High number of mitoses during gametogenesis</p> Signup and view all the answers

    What type of mosaicism is limited to somatic cells?

    <p>Somatic mosaicism</p> Signup and view all the answers

    What is the characteristic of Juvenile Huntington's disease?

    <p>Stiffness or rigidity in joints</p> Signup and view all the answers

    What is the typical number of CAG repeats seen in Juvenile Huntington's disease?

    <p>80-100</p> Signup and view all the answers

    What is the percentage of Huntington's cases that are classified as Juvenile HD?

    <p>5%</p> Signup and view all the answers

    What is the location of the Huntingtin gene that is responsible for Huntington's disease?

    <p>4th chromosome</p> Signup and view all the answers

    What is the earliest reported age of onset for Huntington's disease?

    <p>2 years old</p> Signup and view all the answers

    What is the characteristic inheritance pattern of Huntington's disease?

    <p>Autosomal dominant</p> Signup and view all the answers

    What is the primary cause of Proteus syndrome?

    <p>Mutation of the AKT1 kinase in a gene that is in mosaic state</p> Signup and view all the answers

    What is the function of neurofibromin in the cell cycle?

    <p>Negative regulation of the Ras protein signal</p> Signup and view all the answers

    What is the inheritance pattern of Neurofibromatosis type I (NF1)?

    <p>Autosomal dominant</p> Signup and view all the answers

    What is the penetrance of the NF1 gene mutation by the age of 5 years?

    <p>100%</p> Signup and view all the answers

    What is the location of the NF1 gene that encodes neurofibromin?

    <p>Chromosome 17, band q11.2</p> Signup and view all the answers

    What is the characteristic feature of Neurofibromatosis type I (NF1)?

    <p>Presence of multiple benign neurofibromas</p> Signup and view all the answers

    What is the percentage of inherited vs. spontaneous mutations in Neurofibromatosis type I (NF1)?

    <p>50% inherited, 50% spontaneous</p> Signup and view all the answers

    What is the expression of the NF1 gene in different cells?

    <p>Expressed in neurons, Schwann cells, oligodendrocytes, astrocytes, and leukocytes</p> Signup and view all the answers

    Study Notes

    Autosomal Dominant Traits

    • Traits or diseases are common in the pedigree and found in every generation
    • Affected individuals are often heterozygote
    • Autosomal dominant disorders may manifest during childhood or adolescence
    • Each affected individual transmits the disease to half of their offspring, independent of sex
    • The probability of transmission is independent of each child

    Variability in Autosomal Dominant Inheritance

    • The manifestation of autosomal dominant diseases in different individuals is usually variable
    • Variations may be due to:
      • Variable Expressivity
      • Incomplete Penetrance

    Incomplete Penetrance

    • An individual who has the genotype for a disease may not exhibit the disease phenotype at all, even though they can transmit the disease gene to the next generation
    • Penetrance rates are estimated by examining a large number of families to determine what proportion of obligate carriers develop the disease phenotype

    Treacher-Collins Syndrome

    • Clinical characteristics:
      • Small mandible
      • Downward palpebral fissures
      • Defect of the lower eyelid (coloboma)
      • Microtia
      • Hearing impairment

    Causes of Incomplete Penetrance

    • Genotypes do not act in isolation
      • Interaction with the wild-type allele
      • Interaction with other loci
      • Interaction with the environment
      • Just chance

    Variable Expression

    • Even when penetrance of a condition is complete, the severity of the disease may vary greatly
    • Possible causes:
      • Genotypes do not act in isolation
        • Interaction with the wild-type allele
        • Interaction with other loci
        • Interaction with the environment or just chance

    Anticipation

    • The tendency of some dominant conditions to become more severe (or have earlier onset) in successive generations
    • Caused by unstable expanding nucleotide repeats
    • Example: Huntington disease - expansion of a polyglutamine repeat in the huntingtin gene on chromosome 4

    Mosaicism

    • When an individual has two or more genetically different cell lines derived from a single zygote
    • Caused by a new mutation
    • Mosaicism can be:
      • Somatic
      • Germ-line

    Huntington's Disease

    • Caused by a mutation in the Huntingtin gene on chromosome 4
    • Responsible for producing the protein Huntingtin
    • CAG expansion on exon 1 of the Huntingtin gene
    • Autosomal Dominant disease, not sex-linked
    • HD onset is found generally in adults around the age of 40
    • Paternal Anticipation is seen in HD due to high number of mitoses during gametogenesis and selection against oocytes with large expansions
    • Age of onset varies based on the number of repeats
    • Juvenile HD is a rare form of HD that initiates before the age of 20, usually with 80-100 CAG repeats

    Neurofibromatosis

    • Type I (NF1) is caused by a mutation in the neurofibromin gene
    • Also known as von Recklinghausen disease or Watson disease
    • Autosomal Dominant neurogenetic disorder
    • Characterized by the presence of multiple benign neurofibromas
    • Affects the bone, nervous system, soft tissue, and skin
    • Clinical symptoms increase over time
    • Neurologic problems and malignancy may develop
    • 50% inherited, 50% spontaneous mutations
    • Autosomal Dominant, does not "skip" generations
    • If a person has the NF gene mutation, they will have NF (100% penetrance by the age of 5 years)

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    Description

    This quiz covers the characteristics of autosomal dominant disorders, including traits and diseases found in every generation, affected individuals, and probability of transmission.

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