biology

Myhre syndrome

Myhre 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 Myhre syndrome rather than just read about it. In short: Myhre syndrome (MS) is an ultrarare genetic disorder caused by dominant gain-of-function (GOF) mutations in the SMAD4 gene. MS mutations are missense heterozygous mutations affecting only Ile500 or Arg496 residues of the SMAD4 protein.

Key takeaways

Myhre 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 Myhre syndrome to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Myhre syndrome from memory before moving on to harder problems.

Reference excerpt

Myhre syndrome (MS) is an ultrarare genetic disorder caused by dominant gain-of-function (GOF) mutations in the SMAD4 gene. MS mutations are missense heterozygous mutations affecting only Ile500 or Arg496 residues of the SMAD4 protein. MS patients exhibit manifestations of connective tissue disease including dysfunction of the integumentary, cardiovascular, respiratory, gastrointestinal, and musculoskeletal systems and is often characterized by proliferative systemic fibrosis. Some of these features are life threatening, such as airway or arterial narrowing (laryngotracheal stenosis or aortic coarctation) and fibroproliferation of tissues including lung, heart, and liver. Consistent with these clinical observations, cells isolated from patients with MS demonstrate increased TGF-β signaling. In contrast, loss-of-function (LOF) mutations in SMAD4 predispose individuals to gastrointestinal polyps, a higher risk of colorectal cancer, and a risk of forming arteriovenous malformations (AVM) a hallmark manifestation of hereditary hemorrhagic telangiectasia (HHT). Patients also have external phenotypes similar to Marfan syndrome. Biologically, SMAD4 plays a prominent role in both canonical TGF-β and other TGF-β superfamily signaling. The systemic manifestations of these two disorders suggest opposite biologic effects, such as the finding of aortic aneurysm in SMAD4-JP-HHT (LOF of SMAD4) versus the aortic hypoplasia seen in Myhre syndrome (GOF in SMAD4).

Signs and symptoms The clinical presentation is variable but includes:

Small at birth Developmental and growth delays Firm skin Keratosis pilaris "Athletic" muscular build Characteristic facial appearance Deafness Hyperopia Variable cognitive deficits Autism spectrum disorders/social disability Tracheal stenosis Premature puberty Heavy menses in females Aortic stenosis Pyloric stenosis The facial abnormalities include:

Short palpebral fissures (opening of the eyes) Maxillary hypoplasia (underdevelopment of the upper jaw) Prognathism (prominent lower jaw) Short philtrum Prominent nose The Musculo-skeletal abnormalities include:

Short stature Stiff joints/stiff gait Scoliosis Straight spine Square body shape Broad ribs Iliac hypoplasia Brachydactyly Flattened vertebrae Thickened calvaria Cardiovascular abnormalities include:

Congenital heart defects Atrial septal defect Ventricular septal defect Patent ductus arteriosus Tetralogy of Fallot Aortic coarctation Aortic stenosis Mitral valve stenosis Aortic hypoplasia Pericardial effusion Pericarditis Restrictive cardiomyopathy Other anomalies

Undescended testes in males

Genetics Myhre syndrome is due to mutations in the SMAD4 gene. This gene encodes a protein - transducer mediating transforming growth factor beta. Some researchers believe that the SMAD4 gene mutations that cause Myhre syndrome impair the ability of the SMAD4 protein to attach (bind) properly with the other proteins involved in the signaling pathway. Other studies have suggested that these mutations result in an abnormally stable SMAD4 protein that remains active in the cell longer. Changes in SMAD4 binding or availability may result in abnormal signaling in many cell types, which affects development of several body systems and leads to the signs and symptoms of Myhre syndrome. The patients of this disease exhibit hypertrophic phenotype in their muscle tissues. Myostatin target genes are found to be downregulated while bone morphogenetic protein (BMP) target genes display both upregulated and downregulated genotypes.

Diagnosis The diagnosis of Myhre syndrome is established in a proband with characteristic clinical findings and a heterozygous pathogenic (or likely pathogenic) variant in SMAD4 detected by molecular genetic testing. Because Myhre syndrome is typically caused by a de novo pathogenic variant, most probands represent a simplex case (i.e., a single occurrence in a family). Rarely, the family history may be consistent with autosomal dominant inheritance (e.g., affected males and females in multiple generations).

Treatment There are currently no disease specific therapies, although the use of losartan has been suggested to prevent fibrosis.

History This disorder was first reported in 1981. It has many similarities to LAPS Syndrome and they both arise from the same mutations in the SMAD4 gene. It is believed that they are the same syndrome.

References This article incorporates text from the United States National Library of Medicine ([1]), which is in the public domain.

External links

Illustrations

Worked examples

Example 1 — a first encounter with Myhre syndrome

Start with the simplest possible case. Write down what Myhre 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 Myhre 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 Myhre 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 Myhre syndrome

In research: Myhre 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 Myhre 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: Myhre syndrome is common in secondary-school and first-year university syllabi. It links to neighbouring topics Rare genetic syndromes, Rare syndromes, Syndromes affecting hearing, so understanding it makes those chapters shorter.
In everyday life: Look for Myhre 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Myhre syndrome” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Myhre syndrome in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Myhre 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 Myhre syndrome out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Myhre syndrome in simple terms?

Why does Myhre 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 Myhre 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 Myhre syndrome.