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Floating-Harbor syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Floating-Harbor syndrome

Floating-Harbor syndrome is a rare genetic disorder characterized by short stature, delayed bone age, and significant speech and language delays.

Overview

Floating-Harbor syndrome involves short stature, delayed mineralization of the bones, and delayed speech development. The condition is named after the Boston Floating Hospital and Harbor General Hospital, where it was first described. While speech delays can be severe, motor skill development is typically comparable to that of other children.

Symptoms

  • Growth and development: Short stature (usually in the lowest 5 percent) and delayed bone age in early childhood.
  • Speech and cognition: Severe expressive language delay and mild intellectual disability.
  • Facial features: A triangular face, low hairline, deep-set eyes, long eyelashes, and a large, distinctive nose with a low-hanging separation (columella) between large nostrils.
  • Additional features: A short distance between the nose and upper lip (short philtrum), thin lips, high-pitched voice, and in males, undescended testes (cryptorchidism).
  • Skeletal abnormalities: Short fingers (brachydactyly), clubbing of fingertips, and curved pinky fingers (clinodactyly).

Causes

The syndrome is caused by mutations in the SRCAP gene. This gene provides instructions for the SRCAP protein, which helps activate the CREBBP gene. The CREBBP gene is critical for regulating cell growth, division, and normal development. Mutations in SRCAP interfere with this activation process, though the exact link between these mutations and the specific symptoms of the syndrome is not fully understood.

Inheritance

Floating-Harbor syndrome is inherited in an autosomal dominant pattern, meaning one copy of the altered gene is sufficient to cause the disorder. Most cases result from new (de novo) mutations in individuals with no family history of the condition, though in rare instances, an affected person may inherit the mutation from a parent.

Frequently Asked Questions

Because expressive speech is far more impaired than receptive language (understanding), children often experience extreme frustration, leading to behavioral outbursts. Early implementation of Augmentative and Alternative Communication (AAC)—such as manual sign language, picture exchange systems, or electronic communication devices—should begin as early as toddlerhood. Establishing reliable communication channels reduces tantrum frequency and fosters overall language development.
Human growth hormone therapy has been utilized in several children with Floating-Harbor syndrome with variable results. While it frequently improves short-term linear growth velocity and lean muscle mass during early childhood, it may not significantly alter final adult height, as bones can mature rapidly upon reaching puberty. Decisions regarding hGH therapy require close supervision by a pediatric endocrinologist who will balance growth velocity against bone age advancement.
Patients require periodic renal and urinary tract ultrasounds due to an increased risk of structural kidney anomalies, cysts, and hydronephrosis. Regular dental exams are critical to monitor for malocclusion, delayed eruption, and high caries risk. Routine audiology screenings are recommended to detect fluctuating conductive or sensorineural hearing loss, and pediatric endocrinologists must track bone age and monitor for early or precocious puberty.
Floating-Harbor syndrome is an autosomal dominant condition caused by mutations in the SRCAP gene, but almost all reported cases are the result of a de novo (spontaneous) mutation in the child. Consequently, if the parents do not carry the mutation upon targeted testing, the recurrence risk for subsequent pregnancies is very low (estimated at 1% or less), reflecting the rare possibility of parental germline mosaicism.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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