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Pathology > Ch 15. Genetics-2 > Flashcards

Ch 15. Genetics-2 Flashcards

1
Q

X-Linked Disorders: Lyon Hypothesis

A

Random inactivation of either paternally or maternally inherited X chromosome occurs in each cell of females
Therefore–normal females are mosaics
X inactivation is regulated by the XIST
gene (Xq13)
The inactivated X is reactivated in germ cells

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2
Q

X-Linked Dominant Disorders

A

Rett Syndrome

Vitamin D Resistant Rickets

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3
Q

Rett Syndrome

A

Mental retardation
Females are infertile
Prenatally lethal in males

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4
Q

Vitamin D Resistant Rickets

A

Normal production and metabolism of Vitamin D
Renal tubular loss of phosphate Interferes with skeletal ossification

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5
Q

X-Linked Recessive Disorders

Lesch-Nyhan Syndrome
Complete lack of HGPRT

A

HGPRT (hypoxanthine guanine phosphoribosyl transferase): involved in the salvage pathway for purine synthesis
It salvages purine bases from the breakdown of nucleic acids
If absent–increased synthesis of purine nucleotides de novo with subsequent increased production of uric acid

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6
Q

Lesch-Nyhan Syndrome

A

Appear normal at birth
May develop normal for months
High uric acid levels
Self mutilation, mental retardation, spasticity
Profound lack of dopaminergic terminals and cells
Gout

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7
Q

Duchenne Muscular Dystrophy

A

Covered in Muscle Disease lectures

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8
Q

Multifactorial Inheritance

A

from combined actions of environment and two or more mutant genes;
Risk of expressing the disorder influenced by the number of mutant genes inherited
; Rate of recurrence is the same for all first degree
relatives; Risk of both identical twins getting disorder

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9
Q

Multifactorial Inheritance

A

Examples:
Congenital heart disease Diabetes mellitus
Cleft lip or palate
Hypertension
Gout

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10
Q

Cytogenetic Disorders

A

Alterations in the number or structure of chromosomes

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11
Q

Normal Chromosome

A

Normal human chromosome complement is expressed as:
46 XX–female
46 XY–male
Euploid: an exact multiple of the haploid
number (23)
Aneuploidy: not an exact multiple of 23

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12
Q

Normal Chromosomes

A

Aneuploidy–Causes Nondisjunction
Anaphase lag
When nondisjunction occurs in gametogenesis, the gametes formed have either an extra chromosome, or one chromosome less.

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13
Q

Cytogenetic Disorders

A

Monosomy of an autosome usually results in the loss of too much genetic material to have a live birth
Monosomy or trisomy of sex chromosomes are compatable with life, but may demonstrate phenotypic abnormalities

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14
Q

Mosaicism

A

Occasionally, mitotic errors in early development give rise to two or more populations of cells in the same individual
Mosaicism affecting the sex chromosomes is relatively common
Autosomal mosaicism is much less common

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15
Q

Chromosomal Aberrations

A

Deletion*
Translocation
Balanced
Robertsonian Fusion Insertion*
Inversion
Ring Chromosome
Isochromosome
* already covered in basic genetics

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16
Q

X-Linked Disorders

A

Majority are X-linked recessive
Fully expressed in males
Heterozygous females may partially express the disease
Carriers

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17
Q

Translocation

A

One segment of a chromosome is transferred to another;
-Balanced reciprocal: single breaks in two chromosomes with exchange of material
-Robertsonian: Also known as centric fusion
A translocation between two acrocentric
chromosomes

18
Q

Inversions

A

A rearrangement that involves two breaks within a single chromosome with inverted reinsertion of the segment

19
Q

Ring Chromosome

A

Terminal ends of the chromosome are lost Remaining chromosome circularizes

20
Q

Isochromosomes

A

Chromosome in which one arm is missing and the other arm is duplicated

21
Q

Cytogenetic Disorders

Trisomy 21 (Down Syndrome)

A

Most common chromosomal disorder
Major cause of mental retardation
~ 95% of affected individuals have trisomy 21, with a chromosome count of 47
Remainder have normal numbers of chromosomes, but extra chromosomal material is present as a translocation

22
Q

Trisomy 21

A

Mostcommoncause: meiotic nondisjunction (~95%)
4%–Robertsonian translocation
1%–mosaics
Parents have normal karyotype
Maternal age–strong influence

23
Q

Trisomy 21: Clinical Presentation

A

Flat face with palpebral fissures and epicanthic folds
Mental retardation (severity varies)
Congenital heart disease
Increased risk for leukemia
Abnormal immune response
Simian crease

24
Q

Trisomy 21: Clinical Presentation

A

In all most all of those over 40 years of age
Neuropathic changes characteristic of Alzheimer’s disease
Current median age of death: 47 years

25
Q

Trisomy13 (Patau’s Syndrome)

A

Caused by meiotic nondisjunction
Associated with increased maternal age Severe mental retardation
Microcephaly, Cleft lip and palate, Cardiac defects
Microphthalmia, Rocker bottom feet, Polydactyly

26
Q

Trisomy 18 (Edwards Syndrome)

A

Mental retardation
Rocker bottom feet
Low set ears
Congenital heart defects

27
Q

Chromosome Deletion Syndromes

A

Cri-du-Chat Syndrome

28
Q

Cri-du-Chat Syndrome

A

Deletion of 5p
Severe mental retardation

Catlike cry
Congenital Heart Disease Hypertelorism
Epicanthus
Retrognathia

29
Q

Cytogenetic Disorders Involving Sex Chromosomes

Klinefelter Syndrome

A

Male hypogonadism which occurs when there are two or more X chromosomes and at least one or more Y chromosomes
Most frequent form of genetic disease involving sex chromosomes

30
Q

Klinefelter Syndrome

A

Principal cause of reduced spermatogenesis and male infertility
Lower mean IQ
Mental retardation is uncommon Hypogonadism: consistentfinding
High FSH and estrogen, low testosterone

31
Q

Klinefelter Syndrome

A

Long limbs
Gynecomastia (increased risk of breast cancer)
Tall, thin
Small genitalia
Eunuchoid body habitus

32
Q

XYY Syndrome

A

Tall
Phenotypically normal Behavioral difficulties?

33
Q

Turner Syndrome

A

Results from complete or partial monosomy of the X chromosome
Characterized by hypogonadism in phenotypic females
~57% lack an entire X chromosome
Remainder:
1/3 lack a portion of one X chromosome
2/3 are mosaics

34
Q

Turner Syndrome

A

Peripheral lymphedema at birth (severe cases)
Congenital heart disease:
-Preductal coarctation of the aorta
-Bicuspid aortic valve
Webbed neck
Short stature
Broad chest, widely spaced nipples

35
Q

Turner Syndrome

A

In adolescents and adults: Failure to develop normal secondary sex characteristics
Amenorrhea (primary)

Increased risk of :
Developing autoantibodies to thyroid gland Glucose intolerance
Insulin resistance

36
Q

Multiple Modes of Transmission

Ehlers-Danlos Syndromes

A

Defect in the synthesis of fibrillar collagen
Mode of inheritance encompasses all three mendelian patterns
Typically involves tissues rich in collagen
-Skin
-joints

37
Q

Androgen Insensitivity Syndrome

A

46 XY
Phenotypically female
Mutation in androgen receptor gene
No ovaries or uterus
Testes within abdomen or inguinal canal
X-linked

38
Q

Triple Repeat Mutations

Fragile X Syndrome

A

Xq27.3
Multiple tandem repeats of CGG
-Normally 29 repeats; Premutations 50 - 200; Mutations: > 200
Severe MR
Enlarged testes
Elongated face
Large everted ears

39
Q

Fragile X Syndrome

A

2nd most common genetic cause of MR Most common inherited cause

40
Q

Fragile X Syndrome

A

Differences from typical X-linked disorders:

  • Carrier males (AKA normal transmitting males)
    Clinically and cytogenetically normal
    Transmit disease to grandchildren through daughters
  • Affected Females:
    30 - 50% of carrier females are affected
  • Risk of phenotypic effects
    Depends on place in pedigree
  • Anticipation
41
Q

Fragile X Syndrome

A

Gene: FMR1
Normally: ~29 repeats
Premutations: 50-200 repeats
Full mutations: 200-4000 repeats
*During oogenesis (not spermatogenesis) the premutations can be converted to full mutations

Pathology (15 decks)

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