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4: Population genetics and sex chromosomes > 13. Genetic causes of Infertility  > Flashcards

13. Genetic causes of Infertility  Flashcards

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Biology 101 flashcards
1
Q

How is infertility defined?

A

Failure to achieve pregnancy after 12 months

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2
Q

What are the 4 main causes of infertility in males?

A
  1. Sex chromosome abnormalities
  2. Structural chromosome rearrangements
  3. Y chromosome microdeletions
  4. CF
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3
Q

What is the most common cause of infertility in males?

A

Klinfelter syndrome - 47,XXY

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4
Q

What is the clinical phenotype of KS?

A

Hypogonadism, infertility due to azoo/oligospermia, decreased endocrine function, speech delay, dev delay, gynaecomastia, small testes, tall stature

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5
Q

Other than KS, what sex chromosome abnormalities cause male infertility?

A
  1. 45,X/46,XY mosaicism
  2. 46,XX male DSD - majority have Yp material including SRY
  3. Y isochromosome
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6
Q

Why can balanced translocations and inversions cause infertility in males?

A

Failure to complete synapsis - activates the meiotic pachytene checkpoint causing cell death

Spermatogenic cells are more vulnerable

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7
Q

How do balanced rearrangements of autosomes impact female fertility?

A

Oocytes bypass pachytene checkpoint –> recurrent miscarriage rather than infertility as gametes are unbalanced so offspring are not viable

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8
Q

What are the common Y chr microdeletions?

A

Azoospermia factor regions

AZFa, AZFb, AZFc

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9
Q

How do Y chr microdeletions arise?

A

Non-allelic homologous recombination

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10
Q

What is the most severe Y chr deletion?

What is the phenotype?

A

AZFa - includes USP9Y & DDX3Y

Sertoli cell-only syndrome (SCOS), bilaterally small testes and azoospermia

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11
Q

What is the most common Y chr deletion?

What is the phenotype?

A

AZFc - includes DAZ genes

Variable phenotype, generally compatible with residual spermatogenesis - 50% chance of retrieval by ISCI

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12
Q

How do CFTR mutations cause infertility?

A

CBAVD - congenital bilateral absence of the vas deferens –> interference with sperm transport

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13
Q

What is the phenotype of CBAVD?

A

Obstructive azoospermia due to CBAVD in almost all CF males

Isolated CBAVD is a CFTR-related disorder

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14
Q

What genotypes can cause isolated CBAVD?

A

1x classical + 1x non-classical
2x non-classical
1x classical + 5T
1x classical + Arg117His with 5T

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15
Q

What is the phenotype of Turner syndrome?

A

Congenital ovarian hypoplasia = POF, streak gonads, infertility, hypergonadotropic hypogonadism

Short stature, webbed neck, skeletal abnormalities, heart defects

Frequently mosaic

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16
Q

Why might an X;autosome translocation carrier be infertile?

A

Males infertile due to disruption of the X-Y bivalent at meiosis

Females infertile if breakpoints are within Xq13-22 critical regions - associated with POF

17
Q

Other than infertility, what might be a consequence of an X;autosome translocation?

A

If XIC is on der(X), the X segment on autosome derivative is not inactivated

Female might therefore be affected by XLR disorder (e.g. DMD)

18
Q

What is the cause of Swyer syndrome?

A

SRY mutations cause 46,XY females

19
Q

What is the phenotype of Swyer syndrome?

A

Complete gonadal dysgenesis

Typical female external genitalial & normal uterus and fallopian tubes but streak gonads leading to amenorrhea, pubertal failure and infertility

Risk of gonadoblastoma

20
Q

How do FMR1 mutations cause infertility?

A

FMR1 CGG premutations (59-200 repeats) associated with FXPOI

21
Q

What are the 4 main causes of infertility in females?

A
  1. Chromosome abnormalities e.g. Turners, balanced rearrangments
  2. Swyer syndrome
  3. FMR1
  4. 46,XX gonadal dysgenesis
22
Q

What other disorders are associated with infertility?

A
  1. Congenital hypogonadotropic hypogonadism - insufficient secretion of pituitary gonadotropins (Kallman, idiopathic, part of syndrome)
  2. Noonan syndrome - similar presentation to Turners
  3. CAH due to 21-hydroxylase deficiency
  4. PWS
  5. Androgen insensitivity syndrome
  6. DM1
23
Q

How is 46,XX gonadal dysgenesis characterised?

A

Female phenotype but fail to proceed through puberty

Hypergonadotropic hypogonadism

Streak gonads

24
Q

What causes 46,XX gonadal dysgenesis?

A

FSHR (AR)

BMP15 (XL) - exclusively affects females who inherited mutation from unaffected father

4: Population genetics and sex chromosomes (10 decks)

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