Prader-Willi Flashcards by c k

Chromosome and region affected?

15q11-q13

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Whats the first typical cytogenetic test for PW?

FISH

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Contrary to what one might have assumed, early in life what are the feeding habits of PW?

Usually severed feeding problems in early life, may necessitate NG tube

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Common male finding in PW?

Undescended testicles

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PW presentation in newborn period

Hypotonia (floppy)
dysmorphic features (almond eyes)
undescended testicles
severe feeding problems
Lighter pigmentation

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PW diagnosis can be made with?

FISH or Microarray -

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PW has an early course of __________ and ______________ which reverses during preschool age when children develop____________ and ____________

failure to thrive
feeding difficulties

hyperphagia
weight gain

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Are PW developmentally delayed?

Mild-moderate developmental delay leading to intellectual disabilities as adults

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Do PW patients have ophthalmologic problems?

Yes, ophthalmologic problems are common - especially strabismus and nystagmus

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How are many PW children treated (medically)?

With GH

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How does GH help PW?

may help control obesity and improve short stature

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What is one of the classic key findings in bambinos with PW, if you drape them with one hand?

They are profoundly floppy :)

hypotonia

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Which gene is deleted/silenced in PW?

SNRPN on chromosome 15

Small nuclear ribonucleoprotein polypeptide N

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In PW are we missing genetic information from the maternal or the paternal allele 15q11-q13?

Paternal allele

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Since region 15q11-q13 is imprinted, what becomes critical for normal phenotype?

That information from both maternal and paternal alleles are present for a person to be normal

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3 ways PWS can arise from 15q11-13 error?

Deletion of paternal allele
Uniparental disomy (2 copies present from one parent) of the maternal allele
Imprinting error causing “virtual” maternal UPD

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So, we know that PWS results from a deletion (or absence of fx) of the paternal 15q11-13 allele… What happens if we have a deletion of 15q11-13 maternal allele?

A completely different disorder known as Angelman syndrome

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In addition to Angelman syndrome and PW syndrome, what are 2 additional problems associated with chromosome 15q?

Maternally inherited 15q interstitial duplication

Isodicentric isochromosome 15q(IDIC15)

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How do we test for PWS vs Angelman?

Methylation testing…

If a deletion is present, a FISH test or a microarray can be done to confirm the diagnosis

Prader Willi Syndrome
Common Medical Issues
Systems (4)

Eyes
Orthopedics
Respiratory
Developmentally

PWS

Eyes?

Strabismus (unaligned)

Nystagmus (involuntary eye)

PWS

Orthopedics

Scoliosis is common

PWS

Respiratory

Obstructive sleep apnea may develop

PWS

Sleep apnea is a contraindication to the use of what?

Growth Hormone

PWS | Developmental

Mild-moderate cognitive disabilities are usually found, and behavioral issues are common

Other Disorders Associated with Chromosome 15q Abnormalities of 15q (3)

Marker chromosomes - inverted duplication Interstitial duplications Deletions (Angelman)

Disorders Associated with Chromosome 15q | Autism?

Linkage disequilibrium between patients with Autism and polymorphisms in the GABA-a-b3 locus on chromosome 15q have been reported *gamma-aminobutryic acid type A is an important NT in the CNS

15q11-q13 chromosome anomalies Maternally derived proximal 15q11-q13 chromosome abomalies are one of the most frequently reported cytogenetic abnormalities in patients with_____

autism maybe related to GABA-a receptor genes?

Supernumerary marker chromosome (15q) | Inverted duplicated isodicentric 15q (IDIC15) associated phenotype?

Autism NOT dysmorphic often hypotonic seizures common

The autism associated with 15q is of maternal or paternal derivation?

maternal

What are supernumerary marker chromosomes?

The karyotype of a person with an sSMC shows that in addition to the 46 chromosomes, there is a 47th extra chromosome, known as a marker chromosome: 47,XX,+mar (for a female) or 47,XY,+mar (for a male). An sSMC can be derived from any of the 24 different chromosomes – that is, chromosomes 1 to 22, an X or a Y chromosome.

Interstitial duplication

A piece of a chromosome can be copied, resulting in a duplication or partial Trisomy

15q interstitial duplication | phenotype

maternal phenotype manifested father no phenotype ``` Autism NOT dysmorphic seizures hypotonia in infancy similar to IDIC 15 ```

How would you test for an interstitial duplication of 15q?

Karyotype may be the best way - you could also see on a micro-array but wouldn't know where extra copy was located Methylation testing would demonstrate maternal inheritance

Angelman Syndrome | Etiology?

15q deletion in PWS/AS region from maternal allele

Angelman detection?

FISH | Uniparental disomy or imprinting errors are detected via methylation studies

Errors in imprinting may be increasind due to what?

Advanced reproductive technologies

Angelman phenotype

``` mildly dysmorphic facies-evolve with age hypotonia in infancy-progressing to spasticity in older patients Intellectual Disability Seizures Autism ```

4 potential ways to get Angelman

1. Deletion in maternal region 2. Mutation in maternal region 3. Paternal uniparental disomy 4. Pseudo unitparental disomy due to methylation error

Chromosome abnormalities associated with chromosome 15... | To summarize, the following syndromes/conditions are caused by abnormalities on chr15: (4)

Prader Willi (paternal deletion) Angelman syndrome (maternal deletion) IDIC 15 (associated with autism, hypotonia, seizures, ID) Maternally inherited interstitial duplication (assoicted with autism/hypotonia/seizures/ID)

Mutations on chromosome 11 are commonly associated with what disorders that vary depending on which imprinting error occurs?

Beckweth-Widermann vs. | Russel Silver

Beckweth-Wiedermann syndrome

Due to imprinting error on chromosome 11 ``` Basically overgrowth Macroglasmia macrosomia hypoglycemia omphalocele ```

Russel silver syndrome

Due to imprinting error on chromosome 11 (opp of Beckwith Wiedermann) Dwarfism

There are growth factors in the area of chromosome 11 associated with which two disorders, explaining why over vs. underexpression may manifest in said disorders What other important gene fnx is found in this region

Beckwith-Wiedermann - overgrowth Russel Silver (Dwarf) Tumor suppressor

Imprinting on chromosome ___ can be associated with cystic fibrosis

From most to least common imprinting genetic disorders | 3 main chromosomes

15 11 7