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Genetics Final > Case #4 Fragile X Syndrome > Flashcards

Case #4 Fragile X Syndrome Flashcards

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1
Q

HOw many people does FXS affect in US? (male vs female)?

A

Male: 1/2500-4000

Female: 1/7000-8000

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2
Q

Prevalance of female (heterozygous) carriers

A

1/130-250 in general population

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3
Q

Prevalence of male (heter) carriers

A

1/250-800

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4
Q

What % of previously undiagnosed mental retardeation in males and females, is due to FXS

A

males: 10%
female: 3%

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5
Q

Why doesn;t Betseys mother or father appear to nogt have FXS

A

If Betsey’s mther had the disease allele, it is possible that she did not exhibit any disease phenotye htat was readily identified; she had a premutation

She wouldn’t have been followed clinically

Genetic testing is expensive

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6
Q

Why is FXS have reduced penetrance in women?

A

b/c women carry an extra X chromosome

During development, X chromosomes are randly selected by cell to be inactivated which prevent Tx of almost the netire X chromosome.

THus, for almsot all x chromcomse gene,s mena nd women have about he same amt of expression.

FMR1 is subject to X inac in females

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7
Q

IF X inactivated

A

in X chrom carryign the disease allel is inactivated in disease-related tissues, thte ndividual is less likely to dispaly a fully recognizable phenotype.
A clinically unaffected mother may give birth to an affected daughter or oson

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8
Q

What are social implicatiosn of having disease for

A

chidlren wth FXS, esp boys, will need special educaitonal prodviers and cannot live independetly

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9
Q

is life expectancy diminsehd?

A

no.

NO end up life condquences are anticipated.

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10
Q

what is the role of genetic counselors

A

interpret tests thta re very complicated to clinician and patient

Explain costs and bnefits of genetic testing, and then prapproves tests with insurance complaines

explains what insureance will cover.

Continutity of care

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11
Q

What is FXS

A

oen of the most common causes of mental delays i males and speecy delays in in females

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12
Q

HOw many CGG repeats in premutaiton

A

55-200

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13
Q

How many CGG repeats in full mutation

A

> 200

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14
Q

waht is queationable repeats

A

45-54

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15
Q

Asymptomaitc females with 55-200 repeats have risk for….

A

twin pregnances

early failure of ovaries to produce vaible pregnancies

very early menoapuase

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16
Q

Males and females with 55-200 repeats are also at risk for FX….

A

Fragile X tremor/ataxia syndrome after age 50

symptoms: loss of balance, tremors, memory loss, mood swings, Parkinson-like symptoms, possibly demetnia

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17
Q

What other DIseases can be mistaken for

A

ADHD: imbalance in NT interactions that may result in inattentive and hyperactive impllsive symptoms of ADHD (need at least 6 symptoms )

Autism (seen in first 3 years of life)

Asperger’s syndoeme

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18
Q

Aphasia

A

few words

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19
Q

what idn of test to Dx FXS

A

Southern BLot

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20
Q

FXS inheritance

A

X-linked Dominant

21
Q

Affected female inheritance

A

pass to 50% of children

22
Q

Affected male inheritance

A

pass to 100% daughters
pass to 0% sons

most common form of intellectual instability in boys

23
Q

What is the cytogenetics of FXS

A

CGG insertion into gene at Xq27.3 - called FMR1 gene

24
Q

fucntion of FMR1 gene

A

not completely undersoot

RNA binding protein that is improtant in SYNAPTIC formation in brain

increase CGG repeats -> inc liklihood of expressivity

25
Q

Diseases with CAG (glutaine) triplet repeat (4)

A
  1. Huntington’s Disease
  2. DRPLA (Denatorubropallidoluysim)
  3. Spinobulbar muscular atrophy
  4. # of spinocerebellar ataxis
26
Q

Resut of CAG expanstion

A

formation of altered protein in affected individuatls

27
Q

Non-poyglutamine triplet repeat

A
  1. FXS
  2. Friedriche’s Ataxia
  3. Myotonic Dystorphy
  4. 2 other spinocerebellar ataxia
28
Q

What allele is causing FXS

A

CGG in “junk” region of X chromosome (5’UTR) of

Does not result in altered protein ,but expanded CGG makes X-chromosome MORE FRAGILE

29
Q

Pre-mutaiton

A

55-200

30
Q

Full mutation

A

> 200 CGG repeats

When full mutation –> FMR1 gene is turned off! no protein in is made

31
Q

What happnes if protein synth of fmR1 turned off?

A

affects synaptic plasticity

32
Q

Male vs Female with full mutaiton: symptoms

A

All males and 1/2 females: are affected with learning disabilties, anxiety disorders, and autistic-like behavior

33
Q

Premutation frm maternal transmisttion

A

can be unstalbe

mothers with premutation can have affected chidlren

34
Q

what determiens risk of premutation expanstion

A

depens on # of CGG repeats in maternal allele and other factors

35
Q

What is expanstion risk

A

much greater in affected families

36
Q

What is genetic anticipaition

A

condition becomes more severe and appears at an earlier age as disorder is passed from one generation to the next

i.e. expansion of CGG occurs in succeeding gnerations

37
Q

What are other disorders with genetic ANTICIPATION

A
  1. Huntington’s Disease
  2. Kennedy Sydnrome
  3. Myotonic Dystorphy
38
Q

What is genetic imprinting

A

Certain genes are expressed in a parent-of -ce…specific manner

phenotype ore sever when transimitted form mother than father

High CGG repeates and mental retardation

39
Q

Most common preseting signs

A

Autistic-like behavior (hand flapping, avoidance of eye contact,0

  1. ADD/ ADHD
  2. IQ 35-70, decreased IQ with age
40
Q

Age Dx usually mad

A

pre-school, elementary school

41
Q

Physcial features

A

elongated face,
large ears
Macroorchidism (large testes)

Impulse control problems
Distractablity
Preservative Speech

42
Q

Why do females have less severe symptoms

A
  1. one normal X chromosome due to X inactivation during development

Decrease PENETRANC wiht full mutaiton in FMR1

May not show learning disabilitys

may suffer social anxiety

May have fertility/premature ovarian failture

43
Q

Comorbidity in females with premutation

A

Hypothyroidism and Fibromyalgia

44
Q

Diagnosis

A

PCR
Southern Blot- look for CGG repeats in FMR1

Ethidium Bromide bindst o DNA after exposrue to UV

45
Q

Translational research

A 
Novartis
Roche
Seaside Therapeutics
Afraxis
GSK3
PDE4
46
Q

Is life expectancy affected in pts with FXS?

A

no

47
Q

What does ABMS

A

American Boards of Medical Specialities

48
Q

What does ABMG

A

American Boards of MEidcal Genetics

Genetics Final (8 decks)

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