What is floating-harbor syndrome?

Floating-Harbor Syndrome (FHS) is an extremely rare genetic condition affecting physical and mental development. The name derived from the two hospitals where the first cases were reported in the 1970s: the Boston Floating Hospital and Harbor General Hospital in California.¹ The exact number of people living with the condition is unknown, as scientists are still learning about it, and some cases may be misdiagnosed, but over 100 cases have been reported in medical research papers.² It is thought that FHS is caused by a mutation of a specific gene, known as the SCRAP gene, that contains the instructions for producing a protein that plays a key part in growth and development. The gene mutation happens by chance and can affect anybody, although an affected parent has a 50% chance of passing it on to their child.³

Symptoms

People with FHS tend to have distinct visible characteristics including:

• They are smaller than average in height for their age (short stature)
• A triangular-shaped face
• Deep-set eyes
• Low-set ears
• Long eyelashes
• A prominent nose, and
• Thin lips^1-3
• Children with the condition may have a delayed bone age, which means their bones resemble those of someone much younger due to an unusually slow rate of bone growth.¹ This tends to normalise between the ages of 6 and 12
• Additionally, there are usually speech and language delays, more commonly affecting expressive language (how somebody expresses their thoughts through speech, facial expressions, or writing) over receptive language (listening to and understanding others). The affected individuals usually have mild to moderate learning difficulties¹
• There may be further behavioural difficulties in children and additional symptoms, as many aspects of typical development can be disrupted, and every case is unique
• The cardiovascular system (consisting of the heart and blood vessels) may also be affected in some cases as congenital (present from birth) heart defects have been previously reported^1,2

It is important for healthcare providers, caregivers, and loved ones to learn about the heart defects associated with FHS to recognise serious symptoms and provide the right treatment and support for the person living with the condition.

The cardiovascular system

Having a brief understanding of the cardiovascular system helps us understand how certain anomalies affect someone’s health. The cardiovascular system is made up of the heart and the blood vessels. The heart is a muscular organ that pumps blood around the body. Blood travels through veins, arteries, and capillaries. Blood provides the oxygen and essential nutrients that all cells of the body require to function.

• The heart is divided into two halves, with each half containing two connected chambers
  • An atrium (upper chamber) and
  • A ventricle (lower chamber
• The left side of the heart pumps blood containing oxygen to the rest of the body
• The right side must pump blood containing no oxygen to the lungs
• There are valves within the heart that are like gates that open or shut to allow the passage of blood
• The components of the heart work together to pump blood around in one direction
• Additionally, there are four major blood vessels leading to and from the heart:
  • The aorta is a large artery that carries blood containing oxygen to the body.
  • The vena cava is a vein, which carries blood containing no oxygen from the body back to the heart
  • The pulmonary artery then transports blood to the lungs to replenish the oxygen within the blood
  • The pulmonary vein carries the blood containing oxygen from the lungs back to the heart. The cycle continues

Cardiovascular anomalies in floating-harbor syndrome

Although uncommon, some people with FHS have been reported to have cardiovascular abnormalities.^1,4,5 Parents, caregivers, and healthcare professionals looking after a person with the condition should know that there may be the presence of heart defects, even though, these are not considered typical features of FHS.⁷ The following cardiovascular issues have been associated with some FHS cases:

Septal defects

The heart has a wall separating the left and right sides (septum). A septal defect means that there is a hole in this wall.

• The hole can be between the atria (atrial septal defect) or in between the ventricles (ventricular septal defect). This means that blood flows between the left and right sides of the heart, which causes further issues
• Small septal defects may close on their own and do not cause any symptoms
• However, larger septal defects require surgery to close the hole⁸

Persistent left superior vena cava

The left superior vena cava is a vein which usually shrinks and disappears during the first weeks of development in the womb. When this does not happen, it is identified as ‘persistent’. It usually causes no symptoms but can occasionally be linked to more serious problems with the heart, such as an abnormal heart rate.⁹

Tricuspid regurgitation

This is sometimes referred to as a ‘leaky valve’. It is an anomaly of the heart valve which is located between the right upper chamber and the right lower chamber. The valve won't shut properly; therefore, there is a backflow of blood, and this may eventually cause damage to the heart.¹⁰

Mesocardia

A condition in which the heart lies in an abnormal position in the centre of the chest. Mesocardia on its own would not usually cause complications.¹¹ A rare yet notable issue associated with the condition is if the affected person ever requires heart surgery, it will be very complicated as some parts of the heart will be more difficult for the surgeons to access.¹²

Coarctation of aorta

A narrowing or tightening of the main blood vessel transporting oxygenated blood to the body (the aorta), causes the heart to work harder, which thickens the left ventricle as a result. This is damaging to the heart and may lead to complications such as heart failure or high blood pressure. The condition can be mild and go unnoticed until later in childhood or severe, requiring treatment shortly after birth. It is treated by a procedure called ‘cardiac catheterisation’ in which surgeons will insert a device to widen the blood vessel.⁸

Tetralogy of Fallot

This is a combination of four rare heart defects:

1. Pulmonary stenosis – The narrowing of the valve: that sits between the right ventricle and the pulmonary artery. This means blood flow from the heart to the lungs is restricted
2. Right ventricular hypertrophy – Abnormally larger right ventricle because it is working harder due to the narrowed pulmonary valve
3. Ventricular septal defect – A hole between the left and right ventricles
4. Over-riding aorta – The aorta grows in the incorrect place, above the ventricular septal defect. The blood that is pumped around the body contains insufficient oxygen

A few complications can arise from this condition, including oxygenated and deoxygenated blood mixing, causing cyanosis (blue skin due to lack of oxygen), high blood pressure, and heart failure.⁸

Risk of cardiovascular anomalies for a person with FHS

As FHS is an extremely rare condition with approximately 100 known cases,² it is difficult to say whether an affected person is more likely to have a cardiovascular anomaly than someone without the condition. However, the fact that several heart defects have been reported in the small number of FHS cases could suggest an increased risk.

Cardiovascular symptoms to watch out for

There is a range of cardiac symptoms that would be cause for concern. Watch out for the general signs of a problem with the heart and seek medical attention for your family member with FHS:⁶

• Cyanosis (a blue hue to the skin)
• Rapid breathing
• Rapid heart rate
• Any swelling such as in the hands, feet, or stomach
• Shortness of breath
• Extreme tiredness
• Fainting during exercise

Treatment

Overall, the treatment for anybody living with FHS is aimed at managing their specific symptoms. Someone with FHS should have a team of healthcare professionals managing their care. For example, that could include doctors who treat problems with the bones and joints (orthopaedists), speech and language therapists, physiotherapists, dental specialists, specialists who treat hearing problems (audiologists) etc. A finding of a heart defect means that a congenital heart disease specialist should be part of the team. If a cardiovascular anomaly is found, it should be monitored throughout a person’s life or treated if it is considered severe.

Treatment differs between types of heart defects. Some abnormalities may cause no symptoms, and the affected person will have regular outpatient checkups to monitor it, while some cases may require surgery, medication (such as diuretics to remove excess fluids in the body) or lifestyle changes to correct it.² To learn more about how different heart defects are treated, click here.

Summary

Floating-Harbor Syndrome (FHS) is a rare genetic disorder caused by a mutation in the SRCAP gene, affecting growth, facial features, speech, and learning abilities. Some individuals may also have congenital heart defects, including septal defects, valve issues, or aortic narrowing, which can lead to symptoms like cyanosis, shortness of breath, and fainting.

While heart defects are not a core feature of FHS, monitoring is essential. Treatment is tailored to each person, involving specialists in orthopaedics, speech therapy, and cardiology if needed. Early diagnosis and medical care help manage symptoms and improve quality of life.