What is Floating-Harbor syndrome

TL;DR: Floating-Harbor syndrome is a rare genetic disorder characterized by distinctive facial features, delayed bone age, and significant speech and language delays. It is caused by mutations in the SRCAP gene, which affects the body's ability to regulate gene expression during development.

What exactly is Floating-Harbor syndrome?

Floating-Harbor syndrome is a rare multisystem developmental disorder. It was first described in the 1970s in two families from the Floating Hospital in Boston and the Harbor General Hospital in Los Angeles, which is how the condition earned its name. Individuals with Floating-Harbor syndrome typically experience a combination of growth hormone deficiency, skeletal abnormalities, and intellectual disabilities. While the severity of symptoms varies greatly from person to person, the condition is lifelong and requires a multidisciplinary approach to care.

What are the primary symptoms and body systems affected?

The clinical presentation of Floating-Harbor syndrome is diverse, but clinicians often identify it through a specific set of physical and developmental markers. The most common features include:

• Distinctive Facial Features: Including a triangular face, deep-set eyes, a prominent nose (often described as bulbous), and a thin upper lip.


• Growth and Skeletal Issues: Significant short stature and delayed bone age. Many children also exhibit brachydactyly (short fingers) or clinodactyly (curved fingers).


• Speech and Language Delays: Almost all individuals with Floating-Harbor syndrome experience expressive language delays, which are often more severe than their cognitive or motor delays.


• Developmental Milestones: Mild to moderate intellectual disability and delayed motor development are frequently reported.

How common is Floating-Harbor syndrome?

Floating-Harbor syndrome is exceptionally rare. To date, only a few hundred cases have been reported in medical literature worldwide. Because it is so rare, it is likely underdiagnosed or misdiagnosed as other developmental delay syndromes. Within our own DiseaseMaps community, 11 people with Floating-Harbor syndrome have joined to share their unique experiences, helping to build a better understanding of the lived reality of this condition.

What causes Floating-Harbor syndrome?

The condition is caused by heterozygous mutations in the SRCAP gene (Snf2-Related CREBBP Activator Protein). This gene provides instructions for making a protein that acts as a co-activator for various genes, essentially helping the body "turn on" genes necessary for normal growth and development. In the vast majority of cases, Floating-Harbor syndrome occurs as a de novo mutation, meaning it is not inherited from the parents but occurs randomly in the egg or sperm cell at conception.

How is this condition differentiated from similar syndromes?

Floating-Harbor syndrome shares some clinical overlap with other genetic conditions, such as Rubinstein-Taybi syndrome or Silver-Russell syndrome. However, the specific combination of the SRCAP mutation, the unique "triangular" facial phenotype, and the specific pattern of delayed bone age helps geneticists distinguish it from these other disorders. Clinical genetic testing, specifically a gene panel or whole-exome sequencing, is the gold standard for reaching a definitive diagnosis.

Next steps

• Consult a Clinical Geneticist: If you suspect a diagnosis, request a referral for genetic testing to confirm the presence of an SRCAP mutation.


• Establish a Care Team: Coordinate care between a pediatric endocrinologist (for growth hormone assessment), a speech-language pathologist, and a developmental pediatrician.


• Join the Community: Connect with other families at DiseaseMaps.org to share resources and coping strategies for navigating the complexities of Floating-Harbor syndrome.

Medical disclaimer: This information is for educational purposes only and does not constitute professional medical advice, diagnosis, or treatment; always seek the advice of your physician with any questions regarding a medical condition.

References

• NIH Genetic and Rare Diseases (GARD) Information Center: Floating-Harbor syndrome overview.


• Online Mendelian Inheritance in Man (OMIM): Entry #136140 (Floating-Harbor syndrome).


• Orphanet: The portal for rare diseases and orphan drugs (ORPHA:3335).


• Hood, R. L., et al. (2012). "Mutations in the transcriptional regulator SRCAP cause Floating-Harbor syndrome." American Journal of Human Genetics.