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Infertiliity > Sex Chromosomes > Flashcards

Sex Chromosomes Flashcards

1
Q

Size of X and Y chromosomes

A 
X = 153 Mb, 195 known gene loci 
Y= 50 Mb and 13 known loci (4 in common with X)
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2
Q

What region do X and Y share?

A

Xpter/Ypter pseudoautosomal region (PAR1) 2.6 mb

Par2 at X/Yqter

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3
Q

What gene is present in PAR1

A

Shox gene

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4
Q

What happens regions of asynopsis on x and y at meiosis

A

Not tolerated at meiosis so form sex vesicles

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5
Q

Where is the x inactivation centre (XIST)?

A

Xq13

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6
Q

Disruption of what area of X is associated with gonadal dysgenesis?

A

Xp11.2-p22.1

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7
Q

Where is the X critical region?

A

Xq13-q26

Breakpoints in this region associated with gonadal dysgensis

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8
Q

Breakpoints in what area of the X critical region is not associated with gonadal dysgenesis?

A

Xq22

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9
Q

Where is the SRY gene? What does sry do?

A

Proximal to PAR on the short arm.

It is the testis determining factor (TDF)

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10
Q

Where is the gonadoblastoma specific region (GBY)?

A

Proximal Yq (just blow centromere)

Several genes associated with infertility

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11
Q

Features of distal Yq?

A 
Heterochromatic block 
Non-coding
Variable length 
Q banding and c band positive 
DAPI Bright on FISH
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12
Q

Incidence of turner?

A

1:2000- 1:5000

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13
Q

True or false: turner is associated with older mother?

A

False- associated with older father- often male X missing

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14
Q

Signs of turner in utero?

A 
Cystic hygroma (excess fluid at nape of neck) 
Inter uterine growth retardation
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15
Q

Symptoms of turners in newborns

A

Small for dates

Lymphadema (excess fluid beneath the skin) of hands and feet

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16
Q

Symptoms of turner in childhood?

A

Short stature (98%)
High arched palate (82%)
Short neck/low hairline (80%)
Hypoplastic widely spaced nipples (78%)

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17
Q

Features of turners in adolescence ?

A

Short stature
Primary ammenorrhea
Delayed puberty

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18
Q

Most common cytogenetics for turner?

A 
55% 45,X
25% 46,X, abnormal X
12-20% 46,X, i(X)(q10)
15% mosaic
Numerical 
Structural
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19
Q

Classic Turner syndrome symptoms

A

20-30% congenital heart malformations
30-60% structural anomalies of kidneys
Streak ovaries
Infertile

20
Q

45,X/46,XX phenotype

A

Taller
Likely secondRy amenhorrea rather than primary
May be fertile /subfertile

21
Q

Phenotype of 45 x/ 46 x, i(x)(q10) or ring r(x)?

A

Less turner. Only short stature and gonadal dysgenesis

Mitotically unstable structural abnormality results in post zygotic generation of the 45,x cell line

22
Q

What is phenotype of 45x /46x with marker of y origin.?

A

Female may be at increased risk of gonadoblastoma (benighted tumour that can turn malignancy)

23
Q

Where is the gonadoblastoma gene found?

A

Proximal Yq. Critical region GBY has candidate gene TSPY

24
Q

True or false: turner phenotype is less severe if Xist is absent

A

False: more sever if absent

Functional disomy!!!!

25
Q

Treatment for turner?

A

Growth hormone treatment for height
Puberty- treat with oestrogen and progesterone
Fertility- oocyte donation- embryo transplant
If Y present - surgery to remove streak ovaries

26
Q

Frequency of Klinefelter syndrome

A

1/500-1/1000

27
Q

When do klinefelters usually present?

A

As adults with fertility issues

Occasionally as children with LD

28
Q

Clinical features of klinefelters?

A

30%-50% gynaecomastia (increased breast carcinoma)
Infertility/azoospermia
Eunuchoid habitus (f minute body type)
IQ reduced relative to sibs

29
Q

Common other chromosomal cases of male infertility

A

45 x/ 46 xy
Y structural abnormalities
Isodicentric y, r(y)
Robertsonian translocation (or other translocation especially involving Acrocentric)

30
Q

Features of 47, XYY

A

1 in 840
Mild clinical manifestation
Tall, prominent forehead, maybe associated with behaviour problems
Normal fertility

31
Q

Features of 47, XXX

A

1 in 1000 newborns
Essentially normal phenotype
Mild Devdel and motor delay wide variation
May have increased risk of having xxx or xxy offspring

32
Q

48, xxxx

A 
Iq 30-80
Normal to tall stature
Speech delay 
Downs like features- epicanthic folds, midface hypoplasia 
Menstrual disorders, reduced fertility 
Additional Xs are maternally derived
33
Q

49,XXxX

A

Moderate to severe MR
Prenatal onset growth deficiency
Microcephaly
Downs like features

34
Q

48,xxxy

A 
Moderate to mild
Genital hypoplasia (reduced in size) 
Mild dismorphisms
Normal height
Usually additional xs from mother
35
Q

49, XXXXY

A 
Moderate to severe (iq 30)
Low birth weight 
Short stature 
Hypogonadism 
Downs like features
36
Q

What does the Shox gene do?

A

Short stature homeobox gene

Deletions found in idiopathic short stature

37
Q

What disorder is caused by mutations in the shox gene?

A

Leri-Weill dyschrondrosteosis (lwd)

Characteristic by disproportionate short stature and a curving of radius (modelling deformity)

38
Q

What is the mode of inheritance of mutations in the shox gene?

A

LWD - pseudoautosomal dominant disorder

Depends on genetic recombination between x and y

39
Q

What disorder is caused by a homozygous loss of the SHOX gene?

A

Langer mesolmelic dysplasia (shortening of arms and legs =mesomelia)

40
Q

Symptoms of Kallmann syndrome?

A

Anosmia (no smell) due to agenesis of the olfactory lobes
Hypogonadism secondary to deficiency of hypothalamic gonadotropin-releasing hormone (GnRH)
Mild MR
Colour blindness

41
Q

2 forms of kallmann syndrome

A

1) AD due to LOF mutations in fibroblast growth factor receptor-1 (FGFR1)
2) sex linked form due to mutation in KAL1 close to PAR

42
Q

Why is there a higher prevalence of Kallmann syndrome in males?

A

KAL1 partially escapes X inactivation

43
Q

Where is KAL1 located?

A

Do

44
Q

What is the cause of X-linked Icthyosis (lizard like)

A

Generalised scaling of the skin

Placental steroid sulfatase (STS) deficiency

45
Q

What is the cause of x-linked icthyosis?

A

Complete o partial deletion of the STS gene mapped to Xp22.3

Infertiliity (4 decks)

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