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raghubaburaj

please help with these isq\'s

6 posts in this topic

guys, i was revising from manchester isq's and i found that the answers did not convince me

1.Prader Willi syndrome has always a paternal origin-- it was true in manchester but i think that it is false as per Oxford text

2. Prader willi children are frequently oppositional- true in Manchester but the Oxford says that they are generally very cheerful but can self harm and have behavioral diificulties

3. hyperphagia manifests in adolescence in Prader Willi- true in Manchester but Oxford says that between ages of 1-4, children of Prader Willi syndrome can start binge eating.

Can anyone help please as i dont know what to believe. thanks

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Hi Ohceedee,

As far as the first ISQ is concerned, I would answer false.

According to Companion 7th edition, 70% of cases of Prader Willi syndrome are due to microdeletion on the chromosome 15 derived from the father.

There is also evidence for Uniparental Disomy, in which there are two copies of maternally sourced chromosome 15 and the chromosome from the father is missing.

I am not sure about the rest of the ISQs. I will probably go by what Manchester Course says.

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Background: Prader-Willi syndrome (PWS) is a chromosomal microdeletion/disomy disorder arising from deletion or disruption of genes in the proximal arm of chromosome 15 or maternal disomy of the proximal arm of chromosome 15. Commonly associated characteristics of this disorder include diminished fetal activity, obesity, hypotonia, mental retardation, short stature, hypogonadotropic hypogonadism, strabismus, and small hands and feet.

In 1887, Langdon-Down described the first patient with PWS as an adolescent girl with mental impairment, short stature, hypogonadism, and obesity and labeled her as having polysarcia. Prader et al reported a series of patients with similar phenotypes in 1956. In 1981, Ledbetter et al identified microdeletions within chromosome 15 as the site for PWS.

Pathophysiology: Prader-Willi syndrome is the first human disorder attributed to genomic imprinting. In disorders attributed to genomic imprinting, genes are expressed differentially based upon the parent of origin. An imprinting center has been identified within 15q11-13; gene expression may be regulated by DNA methylation at cytosine bases. Prader-Willi syndrome results from the loss of imprinted genomic material within the paternal 15q11.2-13 locus. The loss of maternal genomic material at the 15q11.2-13 locus results in Angelman syndrome.

Most cases of PSW involving deletions, unbalanced translocations, and uniparental (maternal) disomy occur sporadically. Approximately 70% of cases of PWS arise from deletion of 15q11-13 on chromosome 15. Twenty-eight percent of cases of PWS arise from maternal uniparental disomy caused by chromosomal nondisjunction.

Several genes have been mapped to the 15q11.2-13 region, including the SNRPN gene, P gene (type II oculocutaneous albinism), UBE3A gene (encodes a ubiquitin-protein ligase involved in intracellular protein turnover) and necdin gene (codes for a nuclear protein expressed exclusively in the differentiated mouse brain). Mutations associated with the maternal UBE3A gene result in Angelman syndrome.

Author: Ann Scheimann, MD, Assistant Professor, Department of Pediatrics, Section of Nutrition and Gastroenterology, Baylor College of Medicine and Johns Hopkins Medical Institution

hope this helps! actually the whole article is pretty good:

http://www.emedicine.com/ped/topic1880.htm

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1. About 70 percent of Prader-Willi syndrome cases are caused by a paternally derived deletion on the long arm of chromosome 15.

2. The remaining cases are attributed to maternal uniparental disomy of chromosome 15, in which both members of the chromosome 15 pair come from the mother.

3. In either case, the paternally derived contribution to this specific region of the genome is missing.

I feel the question will be more accurately phrased in the exam and it may be correct to say:

ALWAYS (IN 100% OF CASES), the paternally derived contribution to this specific region of the genome is missing.

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