SMAD4 Gene

Myhre syndrome is a rare condition that affects connective tissue. Connective tissue provides strength and flexibility to structures throughout the body. Myhre syndrome has a variety of signs and symptoms that affect many parts of the body, though not everyone has all the possible features. The features of the condition can range in severity, and some features become more apparent with age.

Common signs and symptoms of Myhre syndrome include short stature, skeletal abnormalities, limited joint mobility, characteristic facial features, intellectual and behavioral problems, hearing loss, a tendency for the buildup of scar tissue (fibrosis) in the skin and internal organs, and heart and lung abnormalities.

Growth is reduced in most people with Myhre syndrome, beginning before birth and continuing through adolescence. Affected individuals usually have a low birth weight and are generally shorter than about 97 percent of their peers throughout life. They have shortened long bones of the arms and legs, unusually short fingers and toes (brachydactyly), and curved pinky fingers (fifth finger clinodactyly). Other skeletal abnormalities associated with this disorder include thickening of the skull bones, flattened bones of the spine (platyspondyly), broad ribs, and underdevelopment of the wing-shaped structures of the pelvis (hypoplastic iliac wings). Affected individuals often have joint problems (arthropathy), including stiffness and limited mobility.

Typical facial features in people with Myhre syndrome include narrow openings of the eyelids (short palpebral fissures), deeply set eyes, a shortened distance between the nose and upper lip (a short philtrum), a narrow mouth with a thin upper lip, an underdeveloped upper jaw, and a protruding lower jaw (prognathism). Some affected individuals are born with an opening in the roof of the mouth (a cleft palate), a split in the lip (a cleft lip), or both. Vision problems are common in this disorder and can include eyes that do not point in the same direction (strabismus), nearsightedness (myopia), farsightedness (hyperopia), an irregular curvature of the front of the eye (astigmatism), clouding of the lenses (cataracts), or rarely, an abnormality of the back of the eye called pseudopapilledema.

Children with Myhre syndrome have delayed development, which is noticeable by age 5. Speech and language delay are the most significant. Motor skills such as crawling and walking may be delayed, although children with Myhre syndrome eventually learn to walk. Most affected individuals have intellectual disability that ranges from mild to moderate, yet some are able to have jobs or pursue higher education.

People with Myhre syndrome typically have behavioral problems like those in autism spectrum disorder, which affects communication and social interaction. These problems vary in severity, and they usually improve over time.

Hearing loss occurs in most people with Myhre syndrome, usually beginning in childhood and gradually worsening. If not detected promptly, hearing problems can contribute to learning and behavioral problems.

Fibrosis in Myhre syndrome can occur in the absence of injury (spontaneously) or develop following surgery or trauma. Affected individuals typically have stiff, thickened skin, usually beginning in childhood. Typically, the skin changes first appear on the palms of the hands, the soles of the feet, the back of the elbows, and the front of the knees. Eventually the skin thickens on other parts of the body. As a result of the thicker skin, affected individuals typically have fewer facial creases (wrinkles) than others of their age. Scars may be more noticeable or become unusually thickened after healing (keloids or hypertrophic scars).

Individuals with Myhre syndrome often have problems with the structure of the heart that are present at birth (congenital heart defects). Fibrosis in the heart and blood vessels (cardiovascular system) can lead to the development of additional problems such as high blood pressure (hypertension) and narrowing (stenosis) of the heart valves or blood vessels. Other cardiovascular problems can include swelling and tightening of the pericardium, which is the membrane that surrounds the heart (pericarditis), and rarely, restrictive cardiomyopathy, in which the heart muscle is stiff and cannot fully relax after each contraction. These cardiovascular problems can be life-threatening.

Abnormalities of the lungs and airways (respiratory tract) in people with Myhre syndrome include narrowing of the windpipe (laryngotracheal stenosis) and the passages leading from the windpipe to the lungs (bronchi); difficulty filling the lungs with air when inhaling (restrictive pulmonary disease); or widespread lung damage (interstitial lung disease). These respiratory tract problems can be life-threatening.

Additional features of Myhre syndrome include problems in the gastrointestinal tract, such as narrowing of the lower part of the stomach (pyloric stenosis) or of the upper part of the small intestine (duodenal strictures) and severe constipation. People with Myhre syndrome also may have an increased risk of developing cancerous or noncancerous tumors, including cancer of the lining of the uterus (endometrial cancer).

Hereditary hemorrhagic telangiectasia is a disorder that results in the development of multiple abnormalities in the blood vessels.

In the circulatory system, blood carrying oxygen from the lungs is normally pumped by the heart into the arteries at high pressure. The pressure allows the blood to make its way through the arteries to the smaller vessels (arterioles and capillaries) that supply oxygen to the body's tissues. By the time blood reaches the capillaries, the pressure is much lower. The blood then proceeds from the capillaries into veins, through which it eventually returns to the heart.

In hereditary hemorrhagic telangiectasia, some arterial vessels flow directly into veins rather than into the capillaries. These abnormalities are called arteriovenous malformations. When they occur in vessels near the surface of the skin, where they are visible as red markings, they are known as telangiectases (the singular is telangiectasia).

Without the normal buffer of the capillaries, the blood moves from the arteries at high pressure into the thinner walled, less elastic veins. The extra pressure tends to strain and enlarge these blood vessels, and may result in compression or irritation of adjacent tissues and frequent episodes of severe bleeding (hemorrhage). Nosebleeds are very common in people with hereditary hemorrhagic telangiectasia, and more serious problems may arise from hemorrhages in the brain, liver, lungs, or other organs.

There are several forms of hereditary hemorrhagic telangiectasia, distinguished mainly by their genetic cause but with some differences in patterns of signs and symptoms. People with type 1 tend to develop symptoms earlier than those with type 2, and are more likely to have blood vessel malformations in the lungs and brain. Type 2 and type 3 may be associated with a higher risk of liver involvement. Women are more likely than men to develop blood vessel malformations in the lungs with type 1, and are also at higher risk of liver involvement with both type 1 and type 2. Individuals with any form of hereditary hemorrhagic telangiectasia, however, can have any of these problems.

Juvenile polyposis/hereditary hemorrhagic telangiectasia syndrome is a condition that involves both arteriovenous malformations and a tendency to develop growths (polyps) in the gastrointestinal tract. Hereditary hemorrhagic telangiectasia types 1, 2 and 3 do not appear to increase the likelihood of such polyps.

Juvenile polyposis syndrome is a disorder characterized by multiple noncancerous (benign) growths called juvenile polyps. People with juvenile polyposis syndrome typically develop polyps before age 20; however, in the name of this condition "juvenile" refers to the characteristics of the tissues that make up the polyp, not the age of the affected individual. These growths occur in the gastrointestinal tract, typically in the large intestine (colon). The number of polyps varies from only a few to hundreds, even among affected members of the same family. Polyps may cause gastrointestinal bleeding, a shortage of red blood cells (anemia), abdominal pain, and diarrhea. Approximately 15 percent of people with juvenile polyposis syndrome have other abnormalities, such as a twisting of the intestines (intestinal malrotation), heart or brain abnormalities, an opening in the roof of the mouth (cleft palate), extra fingers or toes (polydactyly), and abnormalities of the genitalia or urinary tract.

Juvenile polyposis syndrome is diagnosed when a person has any one of the following: (1) more than five juvenile polyps of the colon or rectum; (2) juvenile polyps in other parts of the gastrointestinal tract; or (3) any number of juvenile polyps and one or more affected family members. Single juvenile polyps are relatively common in children and are not characteristic of juvenile polyposis syndrome.

Three types of juvenile polyposis syndrome have been described, based on the signs and symptoms of the disorder. Juvenile polyposis of infancy is characterized by polyps that occur throughout the gastrointestinal tract during infancy. Juvenile polyposis of infancy is the most severe form of the disorder and is associated with the poorest outcome. Children with this type may develop a condition called protein-losing enteropathy. This condition results in severe diarrhea, failure to gain weight and grow at the expected rate (failure to thrive), and general wasting and weight loss (cachexia). Another type called generalized juvenile polyposis is diagnosed when polyps develop throughout the gastrointestinal tract. In the third type, known as juvenile polyposis coli, affected individuals develop polyps only in their colon. People with generalized juvenile polyposis and juvenile polyposis coli typically develop polyps during childhood.

Most juvenile polyps are benign, but there is a chance that polyps can become cancerous (malignant). It is estimated that people with juvenile polyposis syndrome have a 10 to 50 percent risk of developing a cancer of the gastrointestinal tract. The most common type of cancer seen in people with juvenile polyposis syndrome is colorectal cancer.