What is Noonan Syndrome?
Noonan syndrome is a genetic condition that guides the development of many parts of the body6. It is caused by a mutation in one of several key genes, which can disrupt how different tissues grow and form6. The signs and symptoms vary greatly from person to person, ranging from very mild to more severe82.
While each individual's experience is unique, the condition commonly affects several key areas, including distinctive facial features, heart function, growth patterns, and other body systems8. Some of these characteristics may become more or less apparent as a person ages. Because of this wide spectrum, understanding the common symptoms is the first step in providing comprehensive care and support52.
Characteristic Facial Features
One of the most recognizable aspects of Noonan syndrome is a set of distinctive facial features8. These characteristics are not static; they change remarkably as a person grows, sometimes becoming more subtle over time. This evolution is a key part of identifying the condition at different life stages.
Eyes and Forehead
The eyes are often a telling feature, typically appearing wide-set (hypertelorism)8. They may also have a downward slant at the outer corners, and the eyelids can appear droopy (ptosis), which sometimes requires corrective surgery to prevent vision problems8. Many individuals have a broad or high forehead and small skin folds on the upper eyelids that cover the inner corners of the eyes (epicanthic folds)8. The irises are frequently a striking pale blue or blue-green8.
Ears and Neck
The ears are characteristically low-set and often tilted backward8. They may also appear thick or fleshy82. Alongside these ear characteristics, many individuals have a short neck with excess skin folds along the sides, creating a "webbed" appearance8. This feature is often most prominent in infancy but can persist, though it may become less pronounced as a person grows taller.
Nose, Mouth, and Jaw
The nose typically has a broad, flattened bridge and a wide, full tip8. The vertical groove between the base of the nose and the upper lip (the philtrum) is often deeply indented8. A high-arched palate is also a common finding8. In infancy, the lower jaw is often small (micrognathia), which can contribute to feeding difficulties or later dental crowding82.
Changes with Age
The overall facial appearance evolves throughout a person's life8. In newborns, the features can be subtle, with a high forehead and wide-set eyes being the most apparent signs9. During childhood, the face may appear more coarse and the features become easier to recognize. As an individual enters adolescence and adulthood, the face tends to elongate into a more triangular shape, and some earlier characteristics might become less obvious8.
Heart Conditions and Noonan Syndrome
Heart conditions are a common and significant aspect of Noonan syndrome, affecting a majority of individuals8. These issues are typically present at birth (congenital) and often lead to the initial diagnosis2. Because of their potential seriousness, regular monitoring by a cardiologist is an essential part of lifelong care5.
- Pulmonary Valve Stenosis: This is the most common defect9. The valve controlling blood flow to the lungs is narrowed because its leaflets are thick and stiff8. This can force the heart to work harder and may require a procedure to improve blood flow8.
- Hypertrophic Cardiomyopathy (HCM): This condition involves an unusual thickening of the heart muscle8. It can make the heart stiff and may obstruct blood flow8. HCM is monitored closely by specialists, as it can change over time9. Regular check-ups help manage symptoms and ensure the heart remains as healthy as possible7.
- Septal Defects: These are holes in the wall (septum) separating the heart's chambers8. An atrial septal defect (ASD) is a hole between the upper chambers, while a ventricular septal defect (VSD) is between the lower chambers8. Large defects can make the heart and lungs work harder and may require surgical repair8.
- Other Cardiac Concerns: A variety of other issues can occur, including problems with other heart valves or a narrowing of the aorta8. A comprehensive cardiac evaluation with an echocardiogram is crucial at diagnosis and at regular intervals to monitor overall heart health52.
Impact on Growth and Stature
Short stature is one of the most consistent features of Noonan syndrome, affecting about half of all individuals6. Growth patterns can be variable, especially in the early years, and understanding them is key to managing expectations and exploring potential interventions92.
Initial Growth in Infancy
Although some infants with Noonan syndrome are born at a typical size, many experience a slowdown in growth during their first year. This is often linked to feeding difficulties, such as a poor suck or frequent spitting up, which can make it hard for the infant to get enough nutrition82. In some cases, a baby may be born smaller than average, beginning on a lower growth path from the start2.
Slower Pace Through Childhood
As children with Noonan syndrome move past infancy, they typically grow at a slower rate than their peers8. They often track along a lower percentile on standard growth charts, and the height difference between them and other children becomes more apparent over time82. This steady but slow growth is a hallmark of the condition2.
Puberty and Final Adult Height
Puberty is often delayed by a couple of years, and the significant growth spurt that typically accompanies it is often reduced or absent82. This lack of a pubertal surge is a major reason why the final adult height is shorter than average82. Because of these combined factors, treatment with growth hormone is sometimes considered to help increase growth speed and improve final height92.
Other Physical Signs and Considerations
Beyond the face, heart, and stature, Noonan syndrome can present a wide range of other physical signs8. These considerations are important for comprehensive care and often require specialized monitoring62.
Skeletal and Musculoskeletal Differences
Many individuals have noticeable differences in their chest and spine8. The breastbone (sternum) may be shaped unusually, either sunken in (pectus excavatum) or protruding (pectus carinatum)8. Curvature of the spine (scoliosis) is also relatively common82. These variations can range from mild to more significant, sometimes requiring monitoring or corrective measures2.
Bleeding and Lymphatic System Concerns
Issues with bleeding are frequently seen, including easy bruising, frequent nosebleeds, or prolonged bleeding after injury82. This is often due to a deficiency in certain blood clotting factors and requires careful management before any surgery82. Separately, the lymphatic system may not have formed correctly, leading to chronic swelling (lymphedema), most often in the feet and lower legs82.
Genital and Kidney Considerations
In males, a common finding is undescended testicles (cryptorchidism)25. This is typically corrected with a routine surgical procedure (orchiopexy) around one year of age52. This standard procedure helps support future fertility and long-term health52. Structural abnormalities of the kidneys can also occur, sometimes leading to more frequent urinary tract infections8.
Hearing and Vision Issues
Problems with hearing and vision are also part of the syndrome8. Hearing loss can result from issues with nerves or the ear's structure, so regular hearing tests are important5. In addition to droopy eyelids (ptosis), other common eye problems include crossed eyes (strabismus) and rapid, involuntary eye movements (nystagmus), which may require glasses or other treatments8.
