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Genetic Disorders Flashcards

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1
Q

What is a common symptom associated with chromosomal disorders involving sex chromosomes?

A

Gynecomastia may be present

Gynecomastia refers to the enlargement of breast tissue in males.

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2
Q

What is the mean IQ in individuals with chromosomal disorders involving sex chromosomes?

A

Somewhat lower than normal, but mental retardation is uncommon.

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3
Q

What is an important genetic cause of reduced spermatogenesis and male infertility?

A

Chromosomal disorders involving sex chromosomes.

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4
Q

How can single-gene disorders with nonclassic inheritance be classified?

A

Into four categories:
* Diseases caused by trinucleotide-repeat mutations
* Disorders caused by mutations in mitochondrial genes
* Disorders associated with genomic imprinting
* Disorders associated with gonadal mosaicism.

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5
Q

What is a key characteristic of trinucleotide-repeat mutations?

A

Expansion of trinucleotide repeats is an important genetic cause of human diseases.

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6
Q

What nucleotides are usually shared in the expansion of trinucleotide sequences?

A

G and C.

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7
Q

In which syndrome do expansions occur during oogenesis?

A

Fragile X syndrome.

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8
Q

In which disease do expansions occur during spermatogenesis?

A

Huntington disease.

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9
Q

What must be done with caution when assigning a disease to complex multigenic inheritance?

A

It depends on many factors, particularly familial clustering and a range of severity levels.

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10
Q

What defines a gene that is considered polymorphic?

A

A gene that has at least two alleles, each occurring at a frequency of at least 1% in the population.

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11
Q

What results from the collective inheritance of many polymorphisms?

A

Complex multigenic disorders.

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12
Q

True or False: The normal allele in X-linked recessive disorders is always inactivated in all cells.

A

False.

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13
Q

List some examples of X-linked recessive disorders.

A
  • Duchenne muscular dystrophy
  • Hemophilia A and B
  • Chronic granulomatous disease
  • Glucose-6-phosphate dehydrogenase deficiency
  • Bruton’s agammaglobulinemia.
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14
Q

What is an example of an X-linked dominant disorder?

A

Vitamin D-resistant rickets.

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15
Q

What are the mechanisms by which unstable trinucleotide repeats cause diseases?

A
  • Loss of function of the affected gene
  • Toxic gain of function by alterations of protein structure
  • Toxic gain of function mediated by mRNA.
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16
Q

What is unique about mitochondrial gene mutations?

A

They exhibit maternal inheritance.

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17
Q

How many genes does human mtDNA contain?

A

37 genes.

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18
Q

What condition is a prototype of disorders caused by mutations in mitochondrial genes?

A

Leber hereditary optic neuropathy.

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19
Q

What is the range of CGG repeats in normal transmitting males and carrier females?

A

55 to 200.

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20
Q

What is the frequency of Fragile X syndrome in affected males and females?

A

1 in 1550 for affected males and 1 in 8000 for affected females.

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21
Q

What are some physical phenotypes associated with Fragile X syndrome?

A
  • Long face with a large mandible
  • Large everted ears
  • Macro-orchidism.
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22
Q

What is the risk of mental retardation for brothers of transmitting males in Fragile X syndrome?

A

9%.

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23
Q

What is the risk of mental retardation for grandsons of transmitting males in Fragile X syndrome?

A

40%.

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24
Q

What unique feature is observed in at least 90% of affected postpubertal males with Fragile X syndrome?

A

Macro-orchidism.

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25
What is the first law of Mendel's laws of inheritance?
Law of segregation.
26
What does the second law of Mendel's laws state?
Law of independent assortment.
27
What does the third law of Mendel's laws state?
Law of dominance.
28
List exceptions to Mendel's laws.
* Codominance * Heterogeneity * Linked transmission patterns.
29
What percentage of Mendelian disorders are familial?
About 80% to 85%.
30
What are Mendelian disorders also known as?
Single gene disorders
31
What pattern of inheritance do Mendelian disorders follow?
Mendelian pattern of inheritance
32
What percentage of mutations in Mendelian disorders are familial?
80% to 85%
33
What do all Mendelian disorders result from?
Mutations in single genes that have large effects
34
How many deleterious genes is each individual estimated to be a carrier of?
Five to eight deleterious genes
35
What is Turner syndrome characterized by?
Hypogonadism in phenotypic females
36
What causes Turner syndrome?
Complete or partial monosomy of the X chromosome
37
What is the most common sex chromosome abnormality in females?
Turner syndrome
38
What happens to fetal ovaries in Turner syndrome?
Develop normally early in embryogenesis but lose oocytes by age 2 years
39
What is the recurrence risk for siblings of an affected individual in autosomal recessive disorders?
25% for each birth
40
What do autosomal recessive disorders include?
Almost all inborn errors of metabolism
41
What is the classic pattern associated with Klinefelter syndrome?
47,XXY karyotype
42
What are genes located in the male-specific region of Y related to?
Spermatogenesis
43
How are X-linked recessive disorders expressed in males?
Males are hemizygous for X-linked mutant genes
44
What is the definition of a mutation?
A permanent change in DNA
45
What type of mutations are transmitted to progeny?
Germ line mutations
46
What are the two basic forms of nuclear chromatin?
* Heterochromatin (dense and inactive) * Euchromatin (dispersed and active)
47
What is epigenetics defined as?
The study of heritable chemical modification of DNA or chromatin that does not alter the DNA sequence
48
What is the complete set of genes or genetic material in the cell of an organism called?
Genome
49
What is the normal human chromosome complement for females and males?
* 46,XX for females * 46,XY for males
50
What is the typical cause of aneuploidy?
Nondisjunction and anaphase lag
51
What is the phenomenon called when some individuals inherit a mutant gene but are phenotypically normal?
Incomplete penetrance
52
What is the phenomenon called when a trait is expressed differently among individuals with the mutant gene?
Variable expressivity
53
What is the main characteristic of autosomal recessive conditions regarding expression?
More uniform expression than in autosomal dominant disorders
54
What are the two main types of mutations?
* Somatic mutations * Germ line mutations
55
What is the primary cause of Klinefelter syndrome?
Presence of an extra X chromosome
56
What percentage of patients with Klinefelter syndrome have mosaic patterns?
15%
57
What is genomic imprinting associated with?
Epigenic differential patterns of DNA methylation at CG nucleotides
58
What does the term 'eupoid' refer to?
An exact multiple of the haploid number of chromosomes (23)
59
What are the two main types of genetic disorders?
* Chromosomal disorders * Disorders related to mutations in single genes with large effects
60
What is the primary function of the proteins encoded by the human genome?
* Enzymes * Structural components
61
What is the estimated number of DNA base pairs in the human genome?
Roughly 3.2 billion
62
What are the three main categories of genetic disorders?
1. Chromosomal Disorders 2. Mendelian Disorders 3. Genetic Diseases ## Footnote These categories help classify genetic disorders based on their underlying mechanisms.
63
What roles do the encoded proteins in the human genome serve?
1. Enzymes 2. Structural components 3. Signaling molecules ## Footnote These proteins are essential for assembling and maintaining all the cells in the body.
64
What percentage of the noncoding regions of the genome provides critical architectural planning?
80% ## Footnote Noncoding regions play a crucial role in the structural organization of the genome.
65
What are the major classes of functional non-protein-coding sequences found in the human genome?
1. Promoter regions 2. Enhancer regions ## Footnote These regions provide binding sites for transcription factors involved in gene expression.
66
What is genomic imprinting?
An epigenetic process that selectively inactivates either the maternal or paternal allele. ## Footnote This process results in important functional differences between alleles inherited from each parent.
67
What is the most common chromosomal disorder?
Down syndrome (Trisomy 21) ## Footnote It is a major cause of mental retardation, with 95% of affected individuals having Trisomy 21.
68
What is mosaicism in the context of chromosomal disorders?
A condition where two or more populations of cells with different chromosomal complements exist in the same individual. ## Footnote This can occur due to mitotic errors in early development.
69
What are the indications for prenatal testing for genetic disorders?
1. Advanced maternal age 2. Parent known to carry a balanced chromosomal rearrangement 3. Fetal anomalies observed on ultrasound 4. Routine maternal blood screening indicating increased risk of Down syndrome or other trisomies ## Footnote Prenatal testing helps identify potential genetic disorders in at-risk fetuses.
70
What is Klinefelter syndrome?
A condition defined as male hypogonadism with two or more X chromosomes and one or more Y chromosomes. ## Footnote The incidence is approximately 1 in 660 live male births.
71
What is gonadal mosaicism?
A condition where a phenotypically normal parent can transmit a disease-causing mutation to offspring through mutated gametes. ## Footnote This can lead to more than one affected child from a parent who appears unaffected.
72
What are the characteristics of Prader-Willi syndrome?
1. Mental retardation 2. Short stature 3. Hypotonia 4. Profound hyperphagia 5. Obesity 6. Small hands and feet 7. Hypogonadism ## Footnote 65% to 70% of cases are associated with a deletion in chromosome 15.
73
What distinguishes Angelman syndrome from Prader-Willi syndrome?
Angelman syndrome includes ataxic gait, seizures, and inappropriate laughter, while Prader-Willi syndrome is characterized by hyperphagia and obesity. ## Footnote Individuals with Angelman syndrome are often referred to as 'happy puppets' due to their demeanor.
74
True or False: The greater the number of X chromosomes, the greater the likelihood of mental retardation.
True ## Footnote This applies regardless of the presence of a single Y chromosome, which determines male sex.
75
What are the indications for genetic testing in older patients?
1. Inherited cancer syndromes 2. Unusual cancer presentations ## Footnote Testing focuses on genetic diseases that manifest later in life.
76
Fill in the blank: The most common cause of trisomy and therefore of Down syndrome is _______.
meiotic nondisjunction ## Footnote This often occurs during the formation of eggs or sperm.
77
What is the incidence of mosaic Down syndrome?
Approximately 1% ## Footnote These individuals have a mixture of cells with 46 or 47 chromosomes due to mitotic nondisjunction during early embryogenesis.
78
What is more common than autosomal aberrations?
Imbalances of sex chromosomes
79
How are imbalances of sex chromosomes tolerated compared to autosomes?
Much better tolerated
80
What type of disorders are associated with sex chromosomes?
Chromosomal disorders
81
What chronic problems do sex chromosome disorders cause?
Subtle problems relating to sexual development and fertility
82
When are sex chromosome disorders often first recognized?
At the time of puberty
83
Are sex chromosome disorders easy to diagnose at birth?
No, often difficult to diagnose
84
Fill in the blank: Sex chromosome disorders cause _______ relating to sexual development and fertility.
subtle, chronic problems
85
True or False: Imbalances of sex chromosomes are less tolerated than autosomal imbalances.
False

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