Myhre syndrome

Myhre syndrome
Myhre syndrome

Myhre syndrome affects growth and development and is characterised by intellectual disability, short stature, unusual facial features, and various bone (skeletal) differences.

The physical signs of Myhre syndrome include some typical facial features with unusually narrow openings of the eyelids (short palpebral fissures), underdevelopment of the upper jaw bone (maxillary hypoplasia), a more prominent lower jaw (prognathism), small mouth with thin upper lip and short distance between nose and lips (a short philtrum). Some children with the condition can also have an opening in the roof of the mouth (a cleft palate), a split in the lip (a cleft lip), or both.

Skeletal anomalies include short stature, square body shape, broad ribs, underdevelopment of the winglike structures of the pelvis (iliac hypoplasia), flattened bones of the spine (platyspondyly), unusually short fingers and toes (brachydactyly) and thickening of the skull bones (thickened calvaria).

Individuals with the condition also tend to have a muscular appearance (muscular hypertrophy), and skin and joint stiffness limiting joint mobility.

Hearing loss, congenital heart defects and constriction of the throat (laryngotracheal stenosis) are also commonly seen in people with Myhre syndrome.

Most have an intellectual disability that ranges from mild to moderate.  Delayed speech and motor skills, such as crawling and walking, are often seen and some have behavioral issues, such as features of autism.  Boys also have undescended testes (cryptorchidism).

The way in which the condition affects someone varies from individual to individual.  The condition is extremely rare with 30 – 40 cases having been reported worldwide.  Both males and females can be affected.

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The treatment of Myhre syndrome is directed toward the specific symptoms that are apparent in each individual. Treatment is likely to require the coordinated efforts of a team of specialists. Paediatricians, speech and language therapists, skeletal specialists (orthopedists), heart specialists (cardiologists), hearing specialists (audiologists), physiotherapists and other health care professionals may need to systematically and comprehensively plan the treatment and management of the condition.

For some with the condition, problems such as congenital heart defects or undescended testes may require surgical intervention.

Genetics and Inheritance

Myhre syndrome is caused by a genetic misprint (mutation) in a gene called SMAD4 on chromosome 18.  The majority of cases of Myhre syndrome are due to a new (spontaneous) mutation in SMAD4 that has occurred around the time of conception, without either parent having the condition.

Each child of an individual with Myhre syndrome has a 50% (1 in 2) chance of inheriting the condition. This is known as an 'autosomal dominant' inheritance pattern.

The SMAD4 gene provides instructions for making a protein involved in transmitting chemical signals within cells.  It is thought that abnormal signaling in many cell types affects the development of several body systems leading to the signs and symptoms of Myhre syndrome.

Genetic Services and Testing

Genetic testing methods change over time. A consultant geneticist from an NHS genetic clinic can arrange testing of the SMAD4 gene, if this is needed, review the inheritance pattern and provide up-to-date screening advice. Families are welcome to seek advice at various times of life from the genetic service or paediatrician. For example, when a child growing up with Myhre syndrome or their siblings want more details, they could ask about the condition for themselves.

Contact other families affected by Myhre syndrome

We will try to put you in touch with other families affected by Myhre syndrome. Fill in the form below and a member of our support team will get back to you within 7 working days.

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