What Causes Floating-Harbor Syndrome?

Medically Reviewed on 12/19/2022
Causes of Floating-Harbor Syndrome
The prognosis of Floating-Harbor syndrome is typically poor due to the severity of symptoms.

Floating-Harbor syndrome (also called Pelletier-Leisti syndrome) is a rare condition. It generally gets apparent in early childhood and is distinguished by the triad of low proportional height with delayed bone age, distinctive facial appearance, and delayed speech development. Although the cause is unknown, it is assumed to be a result of a genetic mutation. 

Causes of Floating-Harbor syndrome

Based on the study results and studies that are now accessible, it is not feasible to make any valid claims concerning the causes of the development of the Floating-Harbor syndrome. However, research has suggested certain traits that could be the potential causes of Floating-Harbor syndrome.

  • Genetics
    • Medical professionals believe that Floating-Harbor syndrome is caused by heterozygous mutations in the SRCAP gene.
    • The SRCAP gene regulates the production of a protein called SNF2, which connects to the CREBBP activator protein. The protein produced by the CREBBP gene helps regulate cell growth and division, as well as for the normal development of the body.
    • Researchers reported at least five genetic mutations in the SRCAP gene may result in an altered SNF2 protein that interferes with the normal activation of the CREBBP gene, causing developmental issues.
    • However, there is no documented link between SRCAP gene mutations and particular signs and symptoms of the disease.
    • Mutations in the SRCAP gene frequently occur as a new (sporadic or de novo) mutation, indicating that the gene mutation occurred exclusively during the development of the child's egg or sperm, with no impact on other family members.
  • May run in families
    • In certain families with cases of Floating-Harbor syndrome, the condition is passed down to the family offspring via autosomal dominant inheritance.
    • The trait is passed down from either an afflicted mother or father to a child. Either parent can pass on the faulty gene.
    • For each pregnancy, the probability of transferring the faulty gene from the afflicted parent to offspring is 50 percent.
    • According to another research, the inheritance could be autosomal recessive. However, in all these cases, the mothers and children were not affected in the same way, indicating a varied clinical manifestation of the syndrome.
  • Gender
    • Floating-Harbor syndrome affects both sexes, but it more commonly affects women.

Further studies are required to confirm the causes and risk factors of Floating–Harbor syndrome.

What are the signs and symptoms of Floating-Harbor syndrome?

Although researchers have established core symptoms, much about the condition remains unknown. Several constraints, including the small number of identified cases, the absence of major clinical investigations, and the potential of additional genes impacting the condition, hinder clinicians from getting a comprehensive picture of the disorder.

Facial abnormalities are the defining aspect of this disease.

Signs and symptoms of Floating-Harbor syndrome

  • Facial features
    • Deep-set eyes
    • Triangular face
    • Wide mouth with a thin vermilion border on the upper lip
    • Long nose with a narrow bridge and broad, bulbous base
    • Low-set ears
    • Abnormally long eyelashes
    • Thin lips
    • A broad, linear mouth
    • A prominent, triangular-shaped nose
  • Voice quality and language
    • Dysarthria (difficulty speaking)
    • Verbal dyspraxia (difficulty or inability to coordinate the precise movements required to produce clear speech)
    • Hypernasality
    • High-pitched voices
    • Severe receptive and expressive language impairment
  • Bodily features
    • Significant delay in bone age
    • Skeletal anomalies
    • Short fingers and toes
    • Broad fingertips or clubbing
    • Short adult stature (average of 140 cm or less)
    • Delayed growth may lead to low birth weight
    • Broad fingertips that give the appearance of clubbing
    • Short, broad thumbs
    • Prominent joints
    • Abnormalities of the collarbones (clavicles)
    • Short neck
  • Behavior
  • Other observations

Floating-Harbor syndrome causes a wide range of symptoms. The person’s short stature is especially noticeable in most cases; they grow to a height of 140 cm or less.

How is Floating-Harbor syndrome diagnosed?

The typical anatomical anomalies of Floating-Harbor syndrome frequently indicate the presence of the disease. Most complaints are at birth or a young age. The malformations in the child are apparent to doctors and parents, prompting appropriate examinations. Molecular genetic testing with facial symptoms confirms the diagnosis of Floating-Harbor syndrome.

Diagnosing Floating-Harbor syndrome

  • Physical and medical history:
    • The attending physician analyzes the symptoms and medical history and possible causes of the disease during the first consultation.
    • Because Floating-Harbor syndrome is a genetic disease, family history is crucial.
    • The malformations of the face indicate the disease.
  • Imaging studies: X-ray technical studies reveal the major delay in bone age.
  • Molecular genetic testing:
    • Detects genetic mutations. A sequence analysis test can detect mutations in the SRCAP gene.
    • If the person exhibits classic facial features of Floating-Harbor syndrome, molecular testing will reveal a mutation in the SRCAP gene.
  • Prenatal diagnosis: Prenatal diagnosis could be possible for families with a known SRCAP gene mutation. DNA extracted from fetal cells can help identify the disease-causing mutation.
  • Pre-implantation genetic diagnosis (PGD):
    • Could be an option if one of the parents has a known genetic abnormality.
    • Performed on embryos created through in vitro fertilization.
    • Examines an embryo to see if it has the same genetic abnormality as its parent. Families considering this option should seek the advice of a certified genetics professional.

What are the treatment options for Floating-Harbor syndrome?

Floating-Harbor syndrome has no known cure. Managing the symptoms and features entail keeping a close eye on the person’s physical and mental health.

Managing symptoms of Floating-Harbor syndrome

  • Early developmental intervention is important to ensure that affected children reach their potential.
  • Most affected children will benefit from occupational, physical, and speech therapy.
  • Additional medical, social, and/or vocational services, including special remedial education, could be beneficial.
  • Ongoing counseling and support for parents will help.
  • Genetic counseling will benefit affected individuals and their families.
  • Growth hormone therapy has been used to treat some individuals with Floating-Harbor syndrome.
  • Additional therapies, along with standard treatment, may depend on specific symptoms.
  • Clinical trials could be recommended for those who have a progressive condition

Floating-Harbor Syndrome is treated symptomatically. In most cases, the children affected receive special education and grants.

What is the life expectancy of people with Floating-Harbor syndrome?

The prognosis of Floating-Harbor syndrome, which occurs rarely, is poor due to the severity of symptoms. Short stature, language difficulties, and changes in facial structure are common long-term effects of this syndrome. Because this disease is primarily genetic and congenital, only gene therapy could improve the prognosis of Floating-Harbor syndrome.

Development of appropriate therapies for Floating-Harbor syndrome is limited because the condition is rare. This worsens the prognosis.

Many have a relatively good life and, in some cases, can manage their daily lives independently. With age, facial abnormalities fade. Regular examinations could be required to correct the complications.

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Medically Reviewed on 12/19/2022
Image Source: iStock image

Floating-Harbor Syndrome. https://www.ncbi.nlm.nih.gov/books/NBK114458/

Floating Harbor Syndrome. https://rarediseases.org/rare-diseases/floating-harbor-syndrome/

Floating-Harbor Syndrome. https://www.rarechromo.org/media/information/Chromosome%2016/Floating-Harbor%20syndrome%20FTNW.pdf