USMLE Step I 2011 Practice and Orientation materials are available already.


The United States Medical Licencing Examination materials for Step I are already available at the USMLE website.

http://www.usmle.org

The materials can be downloaded in pdf format in:

http://www.usmle.org/Examinations/step1/2011Step1.pdf

The content outlines for this exam has been updated by a subcommittee of the step I committee.

The updated content can be found in this link:

http://www.usmle.org/Examinations/step1/step1_content.html

USMLE committee recommends to students considering to exam Step I after May 2011 to be familiarized with the previous (2010) and the updated content outlines.

In future posts we will discuss the topics associated to the sample questions related to Biochemistry that are included in these materials.

“Extraordinary Measures” – A Movie about Pompe’s Disease


 

Extraordinary Measures is a 2010 film about parents trying to save their children affected by Pompe Disease, A Glycogen Storage Disease produced by mutations on a gen that makes the enzyme acid alpha Glycosidase (GAA), a lysosomal hydrolase.

 Pompe disease is a rare (estimated at 1 in every 40,000 births), inherited and often fatal disorder that disables the heart and muscles.

The movie is based on the true story of John and Aileen Crowley, whose two youngest children were affected with Pompe Disease.

The real John Crowley

As you know Glycogen storage diseases are genetic enzyme deficiencies that result in excessive glycogen accumulation within cells. Additional symptoms depend on the particular enzyme that is deficient.

There are different forms of Glycogen Storage Diseases (aka Glycogenoses), including the Type Ia GSD or Von Gierke’s disease, caused by hepatic deficiency of Glucose 6 Phosphatase, the Type IV or Andersen’s Disease, caused by deficit of branching enzyme in various organs, including the liver, and the GSD Type V or McArdle’s Disease (caused by muscle deficiency of Glycogen Phosphorylase), among others.

GSD Type II or Pompe’s Disease was described by Pompe in 1932, when he studied a girl who suffered from a cardiopathy caused by glycogen accumulation.

The National Institute of Neurological Disorders and Stroke (NINDS), an Institute of the National Institutes of Health System, describe the disease in these terms:

 

“Early onset (or infantile Pompe disease is the result of complete or near complete deficiency of GAA.  Symptoms begin in the first months of life, with feeding problems, poor weight gain, muscle weakness, floppiness, and head lag. Respiratory difficulties are often complicated by lung infections.  The heart is grossly enlarged. More than half of all infants with Pompe disease also have enlarged tongues.  Most babies with Pompe disease die from cardiac or respiratory complications before their first birthday. 

 

Late onset (or juvenile/adult) Pompe disease is the result of a partial deficiency of GAA.  The onset can be as early as the first decade of childhood or as late as the sixth decade of adulthood.  The primary symptom is muscle weakness progressing to respiratory weakness and death from respiratory failure after a course lasting several years.  The heart may be involved but it will not be grossly enlarged.  A diagnosis of Pompe disease can be confirmed by screening for the common genetic mutations or measuring the level of GAA enzyme activity in a blood sample — a test that has 100 percent accuracy.  Once Pompe disease is diagnosed, testing of all family members and consultation with a professional geneticist is recommended.  Carriers are most reliably identified via genetic mutation analysis.

A diagnosis of Pompe disease can be confirmed by screening for the common genetic mutations or measuring the level of GAA enzyme activity in a blood sample — a test that has 100 percent accuracy.  Once Pompe disease is diagnosed, testing of all family members and consultation with a professional geneticist is recommended.  Carriers are most reliably identified via genetic mutation analysis.”

“…Individuals with Pompe disease are best treated by a team of specialists (such as cardiologist, neurologist, and respiratory therapist) knowledgeable about the disease, who can offer supportive and symptomatic care.  The discovery of the GAA gene has led to rapid progress in understanding the biological mechanisms and properties of the GAA enzyme.  As a result, an enzyme replacement therapy has been developed that has shown, in clinical trials with infantile-onset patients, to decrease heart size, maintain normal heart function, improve muscle function, tone, and strength, and reduce glycogen accumulation.  A drug called alglucosidase alfa (Myozyme©), has received FDA approval for the treatment of infants and children with Pompe disease.  Another alglucosidase alfa drug, Lumizyme©, has been approved for late-onset (non-infantile) Pompe disease. ..”

“…Without enzyme replacement therapy, the hearts of babies with infantile onset Pompe disease progressively thicken and enlarge.  These babies die before the age of one year from either cardiorespiratory failure or respiratory infection.  For individuals with late onset Pompe disease, the prognosis is dependent upon the age of onset.  In general, the later the age of onset, the slower the progression of the disease.  Ultimately, the prognosis is dependent upon the extent of respiratory muscle involvement. …”

 It is interesting that even when the Acid Alpha-glycosidase is only involved in the degradation of about 3 % of the Glycogen, its deficit provokes such important damages. Since this enzyme is not related to the main pathways of degradation of glycogen, its deficit does not produce hypoglycemia or a direct lack of metabolic energy. Cellular damage is caused mainly by accumulation of glycogen in the cytoplasm and the lysosomes.

As describe above, nowadays the treatment is based on the use of a recombinant human acid Glycosidase as a replacement of the normal enzyme.  “Extraordinary Measures” describes, in fact, the events that triggered the development of the enzyme for the treatment of this disease.

My favorite quotes of this movie:

John Crowley (Looking at the college-aged kids hired to work under Dr. Stonehill):

-These guys make me feel old.
Dr. Robert Stonehill:

- Scientists get all sensible & careful when they get old. Young ones like risk, not afraid of new ideas… and you can pay ‘em less.

 

John Crowley (talking with Dr. Stonehill after an argument):

-  “Fine, spend the rest of your life dreaming up great ideas that don’t get funded. Draw your diagrams on the wall that cure diseases in theory but never help a single human being in reality.”

 

John Crowley (arguing with a corporate executive about drug research):

-  “This is not about a return on an investment, it’s about kids. Kids with names, dreams, families that love them.”

 

Recommended articles and links:

NINDS Pompe Disease Information Page

Ibrahim, J.; McGovern, M. M.

Glycogen Storage Disease Type II

Some pictures of the Crowley family

How many calories in an Apple Pie?


 

Of course, there are many different apple pies, and many different serving portions  too!!!

So…let’s do the calculations with a “standar” apple pie…certainly not the best but it is standard, so standard that it is the same all around the world!

Of course, I am talking about the MacDonald Apple pie!

Nutrition facts of the Macdonald baked Apple pie (taken from the label):

Proteins 2g

Fat 13 g

Carbohydrates 32 g

Sodium 170 mg

How many calories are obtained when you eat 1 serving size of this pie?

Glycoconjugates and Membrane Carbohydrates


 

Cells recognize one another because of the saccharides attached to cell surfaces. 

They  are present usually as oligosaccharides associated through covalent links to lipids and/or proteins forming Glycoconjugates. The lipid or protein part is integrated into the cell membrane structure, with the saccharide part towards the external membrane surface.

Membrane carbohydrates  (2-10% of the membranes) are on the extracellular surface bounded to lipids or proteins of the membrane, forming glycoconjugates that serve as docking sites in cell recognition, adhesion and receptor action. These sugars include mainly glucose, galactose, mannose, fucose, N-acetyl galactosamine and  N-acetyl glucosamine.

The different kinds of Glycoconjugates include:

Proteoglycans: In the Proteoglycans, the Glucosaminoglycan moety forms the greater fraction of the molecule (tipically a proteoglycan consists of 95 % of carbohydrates) and is the main site of biological activity, providing multiple binding sites. They are found mainly in the extracellular matrix. They are major components of connective tissue.

Glycoproteins: Membrane bound glycoproteins participate in a wide range of cellular phenomena, including cell recognition, cell surface antigenicity, etc. In the glycoproteins, the majority of the molecule consist of proteins; they have one or more oligosaccharides attached to a protein, and they usually are branched and do not have serial repeats, so they are rich in information, forming highly specific sites for recognition and high affinity binding by other proteins

Glycolipids: are membrane lipids in which the hydrophilic head groups are oligosaccharides.

 As in glycoproteins, glycolipids  act as specific sites for recognition by carbohydrate binding proteins.  The four types of human RBC have different oligosaccharides (antigens) in their cell membranes. Blood groups depends on the gangliosides (a kind of sphingolipid) in the surface of the RBC .