What Is Floating Harbor Syndrome?

Floating Harbor Syndrome (FHS), named after the Boston Floating Hospital and Harbor General Hospital, where the disease was first reported, is a rare genetic disorder caused by changes in the SRCAP gene (a unit of genetic information passed on to a child from its parents). FHS can have a range of symptoms affecting different organs and parts of the body. Most frequently, these include low birth weight, reduced height, speech problems and physical abnormalities.² Due to the rarity of FHS, research into the condition is limited and currently ongoing. This article will provide a brief overview of the condition and outline the causes, symptoms, diagnosis and treatment methods available. 

Causes of floating harbor syndrome

Genes make up our DNA. They are passed on to children from their parents. Some of these inherited genes contain the necessary information required to code for proteins. Proteins are a major component of cells, and cells are what makeup tissues.¹  Consequently, genes are responsible for determining our physical and biological characteristics, such as eye colour and height. When a gene contains an error (or mutation), it can be responsible for causing a genetic disorder.

Mutations in the SRCAP gene found in human DNA are responsible for FHS. This mutation can be passed on from an affected parent to their offspring. Only one parent needs to have the mutation to pass on the condition to the child, and each child of an affected parent has a 50% chance of inheriting the altered gene.² This is called an autosomal dominant mode of inheritance. 

More commonly, the cause of FHS is sporadic (de novo) mutations in the SRCAP gene.²  This is when FHS is caused by a brand new mutation in the SRCAP gene, which is not inherited from the parents and that neither parent has in their own DNA. 

Symptoms of floating harbor syndrome

Symptoms of FHS can be identifiable from birth and during childhood.² FHS may affect an array of body systems, but not all people with FHS will exhibit every symptom mentioned below. 

Clinical features

The features of FHS can be subdivided into the following groups:²

• Growth delay - one of the main features of FHS is short stature. Children with FHS may also have low birth weight and reduced growth during childhood. 
• Distinct craniofacial features - including triangular face shape, thin upper lip, long nose with a wide base and low-set ears.
• Intellectual disability - deficits in speech and language are common in children with FHS. Expressive language is usually affected. Some children have difficulty speaking (dysarthria) and may have a nasal or high-pitched voice. Others may show difficulty in understanding words. Individuals with FHS may also have learning disabilities as well as mild to moderate intellectual disability.
• Behavioural difficulties - children with FHS may experience hyperactivity, aggressive behaviour, temper tantrums, impulsivity and restlessness. They may also experience anxiety and features of obsessive-compulsive disorder. These issues tend to improve during adulthood.
• Skeletal malformations - including a short neck and broad chest with a stocky build. Other deformities include those of the hand, such as short thumbs, short finger bones (metacarpals) and broad fingertips. Some individuals have also been reported to have 11 pairs of ribs instead of 12, abnormal curvature of the spine (kyphoscoliosis) and abnormally formed hips (hip dysplasia).
• Dental problems - including dental caries, small teeth (microdontia), loss of baby teeth (primary teeth) at an older age and issues with bites. 
• Cardiac malformations 
• Gastrointestinal conditions - gastro-oesophageal reflux, gluten intolerance, and coeliac disease have all been reported.
• Poor vision - farsightedness (hyperopia) and abnormal squint of the eyes (strabismus) have been reported.
• Hearing loss 
• Early puberty 
• Genital abnormalities - in those with male sexual organs, the testes can be undescended, the urethra can be located at the underside of the penis, and there may be epididymal cysts present.
• Kidney abnormalities - including renal cysts, renal disease, accumulation of urine in the kidneys (hydronephrosis), and complete absence of the kidneys (renal agenesis).
• Seizures

Diagnosis of floating harbor syndrome

Clinical assessment

Initially, a thorough history should be taken by the healthcare team to determine which symptoms are present. However, not all physical features of FHS are evident from a young age, and many features of FHS are also present in other conditions. This can make it difficult to diagnose FHS based on the clinical assessment alone. 

Genetic testing

Because scientists know which gene is responsible for FHS, they can use molecular genetic testing to determine a diagnosis by looking at the DNA in close detail to identify mutations. These are specialist tests which should be discussed with the relevant healthcare professionals. 

If a parent is already known to have a mutation in the SRCAP gene, their unborn child can be assessed for having the same mutation through prenatal testing. There are two methods for this: chorionic villus sampling (where a sample of cells of the placenta is taken for genetic testing) and amniocentesis (where a sample of cells from the amniotic fluid surrounding the baby in the womb is tested for genetic conditions). Similarly, if a couple is going through in-vitro fertilisation (IVF) in order to conceive, the embryo can be tested prior to implantation via a process called pre-implantation genetic diagnosis. 

Treatment of floating harbor syndrome

Because of the range of symptoms associated with FHS, it is important that a thorough medical examination is undertaken by the relevant specialists after a diagnosis has been made. 

These tests may include:²

• Growth monitoring
• Assessment of developmental milestones
• Eye examination
• Hearing tests
• Dental examination
• Renal ultrasound scan
• Blood pressure monitoring
• Orthopaedic assessment

If any conditions are identified through this evaluation, referral to the appropriate specialists should be made to begin the suitable treatment and to arrange ongoing management. This would typically involve a group of multiple healthcare professionals, each being a specialist in their field. 

There may also be local organisations that can provide advice and support for parents of children diagnosed with FHS. 

Prognosis

Due to the small sample sizes in many case studies researching FHS, it is difficult to determine the prognosis of those living with the condition. 

Summary

Floating Harbor Syndrome is a rare condition with many clinical manifestations. Due to the broad spectrum of symptoms it can present, it is important that the medical team perform a thorough clinical exam, as well as the appropriate genetic tests, to determine the correct diagnosis and begin treatment accordingly.