biology

Imerslund–Gräsbeck syndrome

Imerslund–Gräsbeck syndrome is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Imerslund–Gräsbeck syndrome rather than just read about it. In short: Imerslund–Gräsbeck syndrome is a rare autosomal recessive, familial form of vitamin B12 deficiency caused by malfunction of the "Cubam" receptor located in the terminal ileum. This receptor is composed of two proteins, amnionless (AMN), and cubilin.

Key takeaways

Imerslund–Gräsbeck syndrome belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Imerslund–Gräsbeck syndrome to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Imerslund–Gräsbeck syndrome from memory before moving on to harder problems.

Reference excerpt

Imerslund–Gräsbeck syndrome is a rare autosomal recessive, familial form of vitamin B12 deficiency caused by malfunction of the "Cubam" receptor located in the terminal ileum. This receptor is composed of two proteins, amnionless (AMN), and cubilin. A defect in either of these protein components can cause this syndrome. This is a rare disease, with a prevalence about 1 in 200,000, and is usually seen in patients of European ancestry. Vitamin B12 is an important vitamin needed for proper functioning of the bone marrow; if deficient, this may lead to decreased marrow output and anemia. Vitamin B12 has two forms, one of which, along with folate, is important in DNA synthesis. Vitamin B12 is sensitive to acid deformation in the stomach, so a molecule called haptocorrin (R-factor), protects it in the stomach. In the small intestine, a molecule named intrinsic factor (IF), allows vitamin B12 to be absorbed in the ileum. IGS is caused by a mutation in the receptors located in the terminal portion of ileum. This is a very rare, and unlikely cause of vitamin B12 deficiency but is a cause nonetheless.

Signs and symptoms Defined as those seen in any macrocytic, megaloblastic anemia:

Anemia: causing fatigue, conjuctival pallor, pale complexion, and in some cases, a mild icterus (yellowing of the eye). Glossitis ("shiny tongue"): shiny, glossy tongue. Cheilosis (stomatitis): Inflammation of the edges of the lips and the oral mucosa. Tabes dorsalis ("subacute combined degeneration of the spinal cord"): This involves the posterior section of the spinal cord and therefore involves proprioception (sense of position), touch, sense of vibration and in severe cases the lateral corticospinal tract, causing spastic paralysis of the limbs. Peripheral neuropathy: tingling sensation in the arms and legs. Pancytopenia: decreased number of blood cells of all lineages (RBCs, leucocytes, platelets), due to decreased bone marrow production. Methylmalonic acidemia: defined as blood having an unusually high concentration of methylmalonyl CoA. Peripheral findings such as hypersegmented neutrophils and large RBCs on high field view of the blood smears. Laboratory findings indicating increased MCV (Mean Corpuscular Volume), decreased Hgb/Hct (indicating anemia), and decreased value of vitamin B12 in the blood. Proteinuria: protein found in the urine detected by analysis or by dipstick. Reversal of all symptoms except neurological symptoms, by intramuscular injection of vitamin B12. Schilling test indicating no radioactive vitamin B12 in the urine. (This test has dropped out of favor and should not be tried in patients with any form of renal failure).

Genetics The disease is autosomal recessive, and can therefore skip generations. Mutations in either amnionless (AMN) or cubilin can be the culprit. Due to its autosomal recessive pattern of inheritance, affected individuals (persons possessing a homozygous recessive genotype) need to undergo genetic counseling to identify the risk of family members who might be heterozygous genetic carriers. Certain mutations on the CUBN or AMN (genes that encode cubilin and amnionless respectively) have been identified through genetic analysis, and ethnic susceptibility of some of the mutations was indicated from the current research. It has been further suggested that mutations on CUBN were restricted to exon 1-28 which encoded amnionless binding domains (EGF) and IF-Cbl binding region of cubilin, while AMN mutations primarily clustered in intron 8-11 and transmembrane domain in exon 10. Some interesting aspects of particular mutations were also elucidated by the researchers, for example, CUBN mutation c.3890C>T; p.Pro1297Leu, was considered to be a Finnish founder mutation presenting mostly in homozygous status, while an AMN mutation c.208-2A>G, which was thought to account for 15% IGS cases around the world, was postulated as an ancient founder mutation that can trace back to approximately 13,600 years ago.

Pathogenesis Vitamin B12, is an essential water-soluble vitamin found in animal products (such as liver, meat, fish, and dairy products). Vitamin B12 is not found in plant sources; a vegetarian diet can be a risk factor for vitamin B12 deficiency. Normal daily intake of vitamin B12 is 7–30 micro gram, cooking has minimal effect on the structure of this vitamin. The minimal daily adult requirement is 1–3 micro gram, and the human body is able to store at any one time about 2–3 milligram, which is sufficient for at least 2 years of impeccable functioning before the source is depleted. In terms of absorption, no more than 2–3 microgram of vitamin B12 can be absorbed on a daily basis, with some 5–10 microgram of the vitamin B12 involved in enterohepatic circulation. This is in general a principal characteristic of water-soluble vitamins, in that no matter the oral intake, there is a certain threshold for intestinal absorption hence, low or non-existent chance of intoxication, as opposed to fat-soluble vitamins. Vitamin B12 has a major function in the nuclear replication of the DNA. It is therefore logical that its deficiency causes decrease bone marrow production, one of the most common manifestations of which is decreased red blood cell production or as it is referred to medically, anemia. Vitamin B12 however has two major forms in the human body:

Deoxyadenosyl B12 or as it is sometimes referred to Ado B12: Ado B12 is essential for acid-base maintenance of the blood, simply because Ado B12 is the catalyst that assists the conversion of methylmalonyl CoA into succinyl CoA. In absence of vitamin B12, levels of methylmalonyl CoA increase, and this is in fact a great way to distinguish folate deficiency macrocytic anemia, from vitamin B12 deficiency anemia. The following is the reaction in which Ado B12, plays a pivotal role: Propionyl CoA → Methylmalonyl CoA → Succinyl CoA

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Imerslund–Gräsbeck syndrome

Start with the simplest possible case. Write down what Imerslund–Gräsbeck syndrome claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Imerslund–Gräsbeck syndrome before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Imerslund–Gräsbeck syndrome ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Imerslund–Gräsbeck syndrome

In research: Imerslund–Gräsbeck syndrome appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Imerslund–Gräsbeck syndrome in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Imerslund–Gräsbeck syndrome is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anemias, Autosomal recessive disorders, Finnish heritage disease, so understanding it makes those chapters shorter.
In everyday life: Look for Imerslund–Gräsbeck syndrome outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Imerslund–Gräsbeck syndrome in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Imerslund–Gräsbeck syndrome means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Imerslund–Gräsbeck syndrome out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Imerslund–Gräsbeck syndrome in simple terms?

Why does Imerslund–Gräsbeck syndrome matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Imerslund–Gräsbeck syndrome?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Imerslund–Gräsbeck syndrome.