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Floating-Harbor syndrome
This syndrome typically leads to challenges with expressive speech, short stature, and bone age delay. It affects individuals from early childhood and is caused by changes in the SRCAP gene.
Overview
Floating-Harbour syndrome is a rare genetic condition primarily affecting development, growth, and speech. Individuals with the syndrome often experience delayed bone maturation, which means their bones appear younger than their chronological age [PMID:30130282]. Other common features include short stature and distinctive facial characteristics. The condition can also lead to challenges with expressive speech, meaning difficulty in communicating thoughts and feelings verbally.
While the specific combination and severity of features can vary among affected individuals, the key clinical signs often guide diagnosis. The syndrome is typically recognised during childhood when developmental delays become apparent. Genetic testing plays a crucial role in confirming a diagnosis.
Symptoms & clinical features
Individuals with Floating-Harbour syndrome often present with a range of symptoms, which can vary in their presentation. Developmental delay is a common feature, with particular difficulties in developing expressive language skills [PMID:24077977]. Children may experience delays in reaching motor milestones such as sitting or walking, though these are typically milder than speech delays.
Distinctive facial features are often observed, including a triangular face shape, deep-set eyes, a broad nose, and a short philtrum (the groove between the upper lip and nose) [PMID:30130282]. Other physical characteristics can include short stature and skeletal abnormalities, most notably delayed bone age. Some individuals may also experience learning difficulties, which range from mild to moderate. Less commonly, problems with kidney function, heart structure, or hearing may be reported.
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Affected organs
Floating-Harbour syndrome primarily affects several body systems, with significant impact on growth and development. The skeletal system is notably affected, leading to short stature and delayed bone maturation, which means bones appear younger than expected for a person's age. This can contribute to growth challenges.
The central nervous system is also involved, impacting cognitive development and speech. Expressive speech difficulties are a hallmark of the syndrome. While not consistently seen in all individuals, there can also be effects on organs such as the kidneys or heart, though these are less common and typically require specific assessment.
Risks & severity
The severity of Floating-Harbour syndrome can vary considerably among affected individuals, even within the same family. While some individuals may experience milder developmental delays and learning challenges, others might have more significant speech difficulties and require greater support [PMID:24077977]. The short stature and delayed bone age are typically consistent findings.
Complications such as kidney or heart issues are less frequent but highlight the importance of comprehensive medical evaluation. The condition is present from birth, and its features typically become apparent during early childhood as developmental milestones are missed. Lifespan is generally not significantly shortened, but quality of life can be impacted by developmental and communication challenges.
Genetic causes
Floating-Harbour syndrome is caused by pathogenic variants, also known as mutations, in the SRCAP gene. This gene provides instructions for creating a protein called Snf2 related CREBBP activator protein. This protein is an essential part of a larger complex within cells.
The SRCAP protein complex plays a critical role in regulating how genes are turned on and off. It does this by modifying chromatin, which is the tightly packed structure of DNA within the nucleus of a cell. Proper regulation of gene activity is fundamental for normal growth and development throughout the body. When the SRCAP gene has a pathogenic variant, the protein it produces may not function correctly, disrupting these vital regulatory processes and leading to the features observed in Floating-Harbour syndrome.
- SRCAP Snf2 related CREBBP activator proteinThe SRCAP gene encodes a protein integral to chromatin remodelling, a process vital for gene expression and proper cellular development.
Inheritance pattern
Floating-Harbour syndrome is inherited in an autosomal dominant pattern. This means that a person only needs one copy of the altered SRCAP gene in each cell to develop the condition. In many cases of Floating-Harbour syndrome, the pathogenic variant occurs spontaneously, meaning it arises as a new change in the SRCAP gene in the affected individual and was not inherited from either parent. This is known as a de novo variant.
If a parent has Floating-Harbour syndrome due to an autosomal dominant variant, there is a 50% chance with each pregnancy that their child will also inherit the altered gene and develop the condition. Genetic counselling can help families understand these inheritance patterns and the implications for future pregnancies and other family members.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
Diagnosis & testing
Diagnosis of Floating-Harbour syndrome is often suspected based on characteristic clinical features, such as developmental delay, expressive speech difficulties, and short stature with delayed bone age. However, a definitive diagnosis requires genetic testing.
Genetic testing for pathogenic variants in the SRCAP gene can confirm the diagnosis. In the UK, individuals suspected of having Floating-Harbour syndrome may be referred to clinical genetics services by their GP or paediatrician. These services can arrange for appropriate genetic testing, which typically involves a blood test. The relevant NHS Genomic Medicine Service (GMS) testing for this condition would fall under an R-code, facilitating a standardised diagnostic pathway.
Management & lifestyle
There is currently no cure for Floating-Harbour syndrome, so management focuses on addressing specific symptoms and providing supportive care. This often involves a multidisciplinary team approach, including paediatricians, speech and language therapists, physiotherapists, and educational specialists.
Speech and language therapy is often a key component of management to help improve communication skills. Educational support tailored to individual learning needs is also crucial. Regular monitoring of growth and development, as well as screening for potential cardiac or renal issues, may be recommended based on the individual's specific presentation. Genetic counsellors can provide essential support and information to families, helping them understand the condition and navigate available resources within the NHS framework.
UK care pathway
In the UK, if Floating-Harbour syndrome is suspected, the initial step typically involves a referral to a paediatrician or a clinical genetics service through your GP. These specialists can assess the clinical features and determine if genetic testing is appropriate. The NHS Genomic Medicine Service provides comprehensive testing, and Floating-Harbour syndrome would be covered under a specific R-code, ensuring a standardised diagnostic pathway. Genetic counsellors are available to support families throughout this process, explaining the implications of genetic testing and diagnosis, and discussing inheritance patterns and family planning.
Frequently asked questions
What is bone age delay?
Bone age delay means that a child's bones appear less mature than expected for their chronological age when examined by X-ray. For example, a 10-year-old child with bone age delay might have bones that look like those of an 8-year-old. This is a common feature of Floating-Harbour syndrome and contributes to short stature.
How is Floating-Harbour syndrome inherited?
Floating-Harbour syndrome is inherited in an autosomal dominant pattern. This means only one copy of the altered SRCAP gene is needed to cause the condition. In most cases, the genetic change is new in the affected individual and not inherited from a parent.
Will my child's speech improve with Floating-Harbour syndrome?
Many children with Floating-Harbour syndrome experience significant challenges with expressive speech. However, with early and consistent speech and language therapy, communication skills can often improve. The extent of improvement varies among individuals.
Is there a cure for Floating-Harbour syndrome?
Currently, there is no cure for Floating-Harbour syndrome. Management focuses on addressing specific symptoms and providing supportive care, such as speech therapy, physical therapy, and educational support, to help individuals reach their full potential.
What kind of doctors will my child see for Floating-Harbour syndrome?
Children with Floating-Harbour syndrome typically see a team of specialists. This may include a paediatrician, a clinical geneticist, a speech and language therapist, a physiotherapist, and potentially other specialists such as a cardiologist or nephrologist, depending on their specific needs.
References
- Adam MP, Bick S, Mirzaa GM. SRCAP-Related Floating-Harbor Syndrome. 1993. PMID: 23193612
- Rots D, Chater-Diehl E, Dingemans AJM. Truncating SRCAP variants outside the Floating-Harbor syndrome locus cause a distinct neurodevelopmental disorder with a specific DNA methylation signature. American journal of human genetics. 2021. PMID: 33909990
- Alanis S, Blair MP, Kaufman LM. Floating-Harbor syndrome with chorioretinal colobomas. Ophthalmic genetics. 2024. PMID: 37722826
- Dobrzynski W, Stawinska-Dudek J, Moryto N. Floating-Harbor Syndrome: A Systematic Literature Review and Case Report. Journal of clinical medicine. 2024. PMID: 38929963
- Bo H, Jiang L, Zheng J. Floating-Harbor Syndrome Treated With Recombinant Human Growth Hormone: A Case Report and Literature Review. Frontiers in pediatrics. 2021. PMID: 34805044
- Yang W, Li R, Chen C. Pediatric floating-harbor syndrome: clinical features and treatment outcomes in a cohort of Chinese children. European journal of pediatrics. 2026. PMID: 41484376
- Patton MA, Hurst J, Donnai D. Floating-Harbor syndrome. Journal of medical genetics. 1991. PMID: 2051457
- Yang YC, Tang Q, Yan LJ. A Case of Floating-Harbor Syndrome with "Growth and Language Development Delay" as Its Clinical Manifestation. Pharmacogenomics and personalized medicine. 2023. PMID: 38116086