00:00 / 00:00
Evolution and natural selection
Independent assortment of genes and linkage
Mendelian genetics and punnett squares
Alagille syndrome (NORD)
Familial adenomatous polyposis
Multiple endocrine neoplasia
Polycystic kidney disease
Treacher Collins syndrome
von Hippel-Lindau disease
Gaucher disease (NORD)
Glycogen storage disease type I
Glycogen storage disease type II (NORD)
Glycogen storage disease type III
Glycogen storage disease type IV
Glycogen storage disease type V
Mucopolysaccharide storage disease type 1 (Hurler syndrome) (NORD)
Niemann-Pick disease type C
Niemann-Pick disease types A and B (NORD)
Primary ciliary dyskinesia
Sickle cell disease (NORD)
Tay-Sachs disease (NORD)
Cri du chat syndrome
Fragile X syndrome
Down syndrome (Trisomy 21)
Edwards syndrome (Trisomy 18)
Patau syndrome (Trisomy 13)
Fabry disease (NORD)
Glucose-6-phosphate dehydrogenase (G6PD) deficiency
Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)
Ornithine transcarbamylase deficiency
Autosomal trisomies: Pathology review
Miscellaneous genetic disorders: Pathology review
Muscular dystrophies and mitochondrial myopathies: Pathology review
0 / 8 complete
0 / 2 complete
Living with Prader-Willi Syndrome- Abbott Philson
Prader-Willi syndrome p. 56
chromosome association p. 62
ghrelin in p. 340, 378
imprinting p. 56
Prader-Willi syndrome is a genetic disorder that, in infancy, causes poor feeding and low muscle tone, and then in childhood, causes overeating, intellectual disability, and low sex hormones starting in childhood.
Prader-Willi syndrome happens when a handful of genes on chromosome 15 aren’t transcribed into messenger RNA and therefore aren’t expressed.
Among these are SNRPN which stands for Small Nuclear Ribonucleoprotein Polypeptide N and a cluster of snoRNAs, which stands for small nucleolar RNAs, and these genes all have protein products that modify other RNAs.
Now, normally, the copies of the genes contributed by the mother, or maternally derived genes, to this region, are silenced, or turned off, and only the genes from dad, or paternally-derived genes, get expressed.
This special genetic process is called imprinting, where only one copy of the gene gets expressed, not both.
And this differs from most genes in the genome, where both the maternal and paternal copies are expressed.
So those maternal copies in this region are imprinted and therefore silenced.
And this silencing of the maternal copies is an epigenetic process.
In the word “epigenetic”, “epi” means outside of, and “genetic” refers to the DNA sequences of A’s, C’s, G’s, and T’s.
So epigenetic silencing of a gene means turning it off while keeping the DNA sequence itself the same.
The Prader-Willi genes get turned off when methyl groups get attached to the DNA, a process that happens way back when the mother was making an egg.
Even after fertilization of the egg and all of the cell divisions it takes to make a person, that epigenetic mark remains, kind of like a reminder to keep those maternally-derived copies of the genes turned off.
Unfortunately, though, this means that if paternal copies of the genes don’t get expressed, then there aren’t any backup copies being expressed, and so no copies get expressed!
And this is what happens in Prader-Willi syndrome!
Now, there are a few ways these paternal genes wouldn’t be expressed.
The most common one is a deletion on the paternal genes spanning Prader-Willi region.
A lot of deletions also include a nearby gene called OCA2, which codes for a pigment that gives color to the eyes, the hair, and the skin.
Prader �Willi syndrome is a rare genetic disorder in which certain genes on chromosome 15 are deleted or unexpressed on the paternal chromosome. Symptoms include low muscle tone, short stature, incomplete sexual development, cognitive disabilities, behavior problems, and a chronic feeling of hunger that can lead to excessive eating and life-threatening obesity. Treatment involves a combination of genetic counseling, medical care, and behavior therapy.
Latest on COVID-19
Nurse Practitioner (NP)
Physician Assistant (PA)
Create custom content
Raise the Line Podcast
Copyright © 2024 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
Cookies are used by this site.
Terms and Conditions
USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.