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Floating-Harbor Syndrome

, MD, FRCPC, FCCMG, FACMG, , MD, FRCPC, FCCMG, and , MD, FRACP.

Author Information

Initial Posting: ; Last Revision: January 24, 2013.

Estimated reading time: 12 minutes

Summary

Clinical characteristics.

Floating-Harbor syndrome (FHS) is characterized by typical craniofacial features; low birth weight, normal head circumference, and short stature; bone age delay that normalizes between ages six and 12 years; skeletal anomalies (brachydactyly, clubbing, clinodactyly, short thumbs, prominent joints, clavicular abnormalities); severe receptive and expressive language impairment; hypernasality and high-pitched voice; and intellectual disability that is typically mild to moderate. Difficulties with temperament and behavior that are present in many children tend to improve in adulthood. Other features can include: hyperopia and/or strabismus; conductive hearing loss; seizures; gastroesophageal reflux; renal anomalies (e.g., hydronephrosis/renal pelviectasis, cysts, and/or agenesis) and genital anomalies (e.g., hypospadias and/or undescended testes).

Diagnosis/testing.

The diagnosis is established by presence of a heterozygous SRCAP pathogenic variant in those with clinical findings of FHS.

Management.

Treatment of manifestations: Early intervention programs, special education, and vocational training to address developmental disabilities; communication rehabilitation with sign languages or alternative means of communication; and behavior management by a behavioral specialist/psychologist with consideration of medication as needed. Referral to an endocrinologist for consideration of human growth hormone (HGH) therapy; however, data on its use in FHS are limited. Standard treatment for refractive errors and strabismus, hearing loss, seizures, gastroesophageal reflux, and renal and genitourinary anomalies.

Surveillance: Close monitoring of growth, especially in the first year. Annual: ophthalmologic evaluation, hearing screening, blood pressure measurement, and assessment of renal function. Sonographic evaluation for renal cysts in teenage/adult years is indicated.

Genetic counseling.

FHS is inherited in an autosomal dominant manner. The majority of affected individuals have a de novo pathogenic variant. Each child of an individual with FHS has a 50% chance of inheriting the pathogenic variant. Prenatal diagnosis is possible for families in which the pathogenic variant has been identified.

Diagnosis

The diagnosis of Floating-Harbor syndrome (FHS) is suspected in those with typical clinical findings (especially facial features) and confirmed by the presence of a heterozygous SRCAP pathogenic variant.

Craniofacial appearance (see Figure 1)

Figure 1. . Facial appearance of a girl age 11 years with FHS (SRCAP pathogenic variant p.

Figure 1.

Facial appearance of a girl age 11 years with FHS (SRCAP pathogenic variant p.Arg2444Ter) A. Note triangular face with deep-set eyes; short philtrum; long nose with narrow bridge and broad base with low hanging columella; and thin upper lip.

  • Triangular face
  • Deep-set eyes
  • Short philtrum
  • Wide mouth with a thin vermilion border of the upper lip
  • Long nose with a narrow bridge, broad base, full tip and low-hanging columella
  • Low-set ears

Other features

  • Significant delay in bone age (-2 SD or greater) with normalization between ages six and 12 years
  • Skeletal anomalies: brachydactyly, broad fingertips that give the appearance of clubbing, clinodactyly, short thumbs, prominent joints, clavicular abnormalities (see Figure 2)
  • Short adult stature: 140-155 cm (see Figure 3)
Figure 2. . Dorsal (A) and palmar (B) view of the hands of the girl in Figure 1.

Figure 2.

Dorsal (A) and palmar (B) view of the hands of the girl in Figure 1. Note clinodactyly, widened fingertips, and prominent joints.

Figure 3. . Frontal view of the girl in Figure 1.

Figure 3.

Frontal view of the girl in Figure 1. She has proportionate short stature with height <3rd centile.

Speech and language

  • Dysarthria and verbal dyspraxia with phoneme imprecision
  • Hypernasality
  • High-pitched voice
  • Severe receptive and expressive language impairment across all domains of function

Intellectual disability. All individuals have some degree of intellectual impairment and/or learning disability ranging from borderline normal to moderate intellectual disability.

Molecular Genetic Testing

Gene. SRCAP is the only gene in which pathogenic variants are known to cause Floating-Harbor syndrome.

Table 1.

Molecular Genetic Testing Used in Floating-Harbor Syndrome

Gene 1Test MethodAllelic Variants Detected 2Variant Detection Frequency by Test Method 3
SRCAPSequence analysis 4Sequence variantsUnknown 5
Sequence analysis of select exons 6Sequence variants in exon 34Observed in 19 patients reported to date 5, 7
1.
2.

See Molecular Genetics for information on allelic variants.

3.

The ability of the test method used to detect a variant that is present in the indicated gene

4.

Examples of pathogenic variants detected by sequence analysis may include small intragenic deletions/insertions and missense, nonsense, and splice site variants; typically, exon or whole-gene deletions/duplications are not detected. For issues to consider in interpretation of sequence analysis results, click here.

5.
6.

Exons may vary by laboratory.

7.

Testing Strategy

To confirm/establish the diagnosis in a proband. The diagnosis of FHS is suspected in those with characteristic clinical findings and confirmed in those with a heterozygous SRCAP pathogenic variant.

Clinical Characteristics

Clinical Description

Prior to the molecular characterization of Floating-Harbor syndrome (FHS) by Hood et al [2012], a number of reports included descriptions of individuals in whom the diagnosis of FHS could be questioned. This GeneReview chapter only includes information on those 19 individuals with molecularly confirmed FHS (i.e., presence of a heterozygous SRCAP pathogenic variant) [Hood et al 2012, Le Goff et al 2013]. The six females and 13 males range in age from 11 months to 32 years.

FHS is frequently recognized in early childhood because of the characteristic facial features (Figure 1). Infants and younger children are often referred for assessment of poor growth or developmental (predominantly speech and language) delay.

Intellect. Although gross motor and fine motor milestones are within normal limits, affected individuals typically have mild to moderate intellectual disability.

A disorder of speech and language is the most severe disability. Most aspects of communication are affected; expressive language is most consistently and severely affected. Speech is absent in some.

The majority of affected children receive mainstream education with individualized educational plans.

Regression of skills is not typical of FHS.

Behavior. Many individuals with FHS have temperament and behavior differences and difficulties: temper tantrums in infancy and attention deficit-hyperactivity disorder (ADHD) spectrum with impulsivity, inattention, and restlessness at school age.

Aggressive and violent outbursts can occur.

Obsessive compulsive disorder (OCD) and anxiety have been observed.

Behavioral problems are reported to improve in adulthood.

Growth. Short stature is a cardinal sign of FHS.

The majority of individuals with FHS have low birth weight (from -3 SD to 0 SD) and normal head circumference (-2 SD to 0 SD).

In the first years of life weight gain and linear growth are poor.

Average adult height is 140-155 cm.

Puberty. Early puberty has been reported; data are insufficient to determine the incidence in either gender.

Eye. Three of 19 patients have been reported with hyperopia and one of 13 with strabismus. One patient had anterior chamber abnormalities.

Hearing. Conductive hearing loss has been seen in three of 19 individuals with FHS. Cochlear abnormality has been observed in one of 19.

Neurologic. Seizures have been observed in three of 19 patients.

Gastrointestinal. Reflux can be severe, requiring G-tube feeding in some. Constipation and colonic strictures have been observed. One of 19 patients had celiac disease; two had transient gluten intolerance.

Genitourinary. Renal and genitourinary anomalies can occur and include hypospadias and undescended testes, epididymal cysts, varicocele, and posterior urethral valves in boys. Hydronephrosis/renal pelviectasis and nephrocalcinosis, renal cysts, and renal agenesis have been observed. One adult of the 19 reported individuals developed polycystic kidney disease and end-stage renal disease (ESRD).

Orthopedic. The body habitus is often stocky with a broad chest and short neck.

Additional features include hand anomalies such as clinodactyly, brachydactyly, short thumbs, and broad fingertips that give the appearance of clubbing (Figure 2).

Clavicular anomalies including pseudarthrosis and clavicular hypoplasia have been observed, as have short metacarpals, 11 pairs of ribs, kyphoscoliosis, dysplastic hips, and dislocated radial heads.

Dental. A number of individuals with FHS have dental problems (e.g., caries, microdontia, delayed loss of primary teeth) and orthodontic problems (e.g., maxillary retrusion, underbite).

Cardiac. Cardiac malformations are not usually a feature of FHS. Of 19 affected individuals one had mild aortic coarctation, one mesocardia with persistent left superior vena cava, and one atrial septal defect.

Prevalence

The prevalence of FHS is not known. Nineteen individuals with a heterozygous SRCAP pathogenic variant have been reported to date [Hood et al 2012, Le Goff et al 2013].

The majority of individuals reported with FHS are of European origin. Whether the occurrence of FHS is lower in non-white populations or the observed difference is the result of other factors is not known.

Differential Diagnosis

The distinctive facial features, bone age delay, and characteristic speech disability that make the diagnosis of Floating-Harbor syndrome (FHS) straightforward in early childhood become less distinct with age. The following conditions should be considered in children in whom the diagnosis of FHS is suspected.

Broad or angulated thumbs and low hanging columella are typically seen in Rubinstein-Taybi syndrome (RSTS). RSTS is characterized by distinctive facial features that include downward-slanting palpebral fissures, low-hanging columella, high palate, grimacing smile, and talon cusps. The clinical diagnosis of RSTS can be confirmed by identification of a heterozygous pathogenic variant in either CREBBP or EP300, the only genes in which mutation is known to cause RSTS. Mode of inheritance is autosomal dominant, with most affected individuals having a de novo pathogenic variant.

Russell-Silver syndrome (RSS) is characterized by intrauterine growth retardation accompanied by postnatal growth deficiency. Affected individuals typically have proportionately short stature, normal head circumference, fifth-finger clinodactyly, typical facial features with triangular facies characterized by broad forehead and narrow chin, and limb-length asymmetry that may result from hemihypotrophy with diminished growth of the affected side. Growth velocity is normal in children with RSS. The average adult height of males is 151.2 cm and that of females is 139.9 cm. Individuals with RSS are at significant risk for developmental delay (both motor and cognitive) and learning disabilities. RSS is a genetically heterogeneous condition and for most affected individuals represents a phenotype rather than a specific disorder.

3-M syndrome is characterized by severe pre- and postnatal growth retardation (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies with relatively large head, triangular face, hypoplastic midface, full eyebrows, fleshy nasal tip, long philtrum, prominent mouth and lips, pointed chin, and normal intelligence. Additional features of 3-M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. The bone age may be slightly delayed. Males with 3-M syndrome have hypogonadism and, occasionally, hypospadias. Characteristic radiologic findings differentiate 3-M syndrome from Floating-Harbor syndrome. Biallelic pathogenic variants in one of three genes – CUL7, OBSL1, and CCDC8 – are now known to cause 3-M syndrome. Mode of inheritance is autosomal recessive.

Management

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs in an individual diagnosed with Floating-Harbor syndrome (FHS), the following evaluations are recommended:

  • Multidisciplinary developmental evaluation including assessment of gross and fine motor skills, speech/language, cognitive abilities, and vocational skills with special attention to speech delay and anomalies
  • Measurement of growth and plotting of growth parameters
    Note: Syndrome-specific charts are currently not available for children with a SRCAP pathogenic variant.
  • Ophthalmologic examination
  • Hearing evaluation (See Deafness and Hereditary Hearing Loss Overview for details of evaluation.)
  • Renal ultrasound examination and blood pressure assessment
  • Assessment for cryptorchidism in males
  • Orthopedic assessment of hip dysplasia and clavicular anomalies
  • Dental evaluation
  • Consultation with a clinical geneticist and/or genetic counselor

Treatment of Manifestations

Treatment includes the following:

  • Early intervention programs, special education, and vocational training to address developmental disabilities
  • Communication rehabilitation with sign languages or alternative means of communication
  • Behavior management strategies including referral to a behavioral specialist/psychologist and consideration of medication if needed
  • Referral of the family to support groups and other resources
  • Standard treatment for any of the following if identified:
    • Refractive errors and strabismus
    • Hearing loss
    • Seizures
    • Renal disease
    • Cryptorchidism
    • Orthopedic complications
    • Dental problems
  • Referral to an endocrinologist for consideration of human growth hormone (HGH) therapy. HGH therapy with modest response has been reported in three children with FHS. Caution is indicated as limited information about HGH therapy in FHS is available.
  • Investigation for celiac disease if indicated by clinical features

Surveillance

Surveillance includes the following:

  • Close monitoring of growth, especially in the first year of life
  • Annual:
    • Ophthalmologic evaluation
    • Audiologic screening; more frequent evaluation if there is a history of multiple episodes of otitis media
    • Blood pressure measurement and assessment of renal function
  • Standard monitoring for renal anomalies
  • Monitoring of bone age and for early puberty especially in cases of growth hormone use
  • Sonographic evaluation for renal cysts in teenage/adult years as indicated by abnormalities on the renal function tests and/or blood pressure measurement

Evaluation of Relatives at Risk

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Pregnancy Management

No specific pregnancy complications for the mother or the fetus have been observed in the two women with SRCAP pathogenic variants who had children with FHS.

Therapies Under Investigation

Search ClinicalTrials.gov in the US and www.ClinicalTrialsRegister.eu in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Genetic Counseling

Genetic counseling is the process of providing individuals and families with information on the nature, inheritance, and implications of genetic disorders to help them make informed medical and personal decisions. The following section deals with genetic risk assessment and the use of family history and genetic testing to clarify genetic status for family members. This section is not meant to address all personal, cultural, or ethical issues that individuals may face or to substitute for consultation with a genetics professional. —ED.

Mode of Inheritance

Floating-Harbor syndrome (FHS) is inherited in an autosomal dominant manner; the majority of affected individuals have a de novo pathogenic variant.

Risk to Family Members

Parents of a proband

Sibs of a proband

  • The risk to the sibs of the proband depends on the genetic status of the proband’s parents.
  • In the rare case of a parent being affected, the risk to sibs of the proband is 50%.
  • When the parents are clinically unaffected, the risk to the sibs of a proband appears to be low.
  • If the pathogenic variant found in the proband cannot be detected in the leukocyte DNA of either parent, the risk to sibs is low but greater than that of the general population because of the theoretic possibility of germline mosaicism.

Offspring of a proband. Each child of an individual with FHS has a 50% chance of inheriting the pathogenic variant.

Other family members. The risk to other family members depends on the status of the proband's parents. If a parent is affected, his or her family members may be at risk.

Related Genetic Counseling Issues

Considerations in families with an apparent de novo pathogenic variant. When neither parent of a proband with an autosomal dominant condition has the pathogenic variant or clinical evidence of the disorder it is likely that the proband has a de novo pathogenic variant. However, possible non-medical explanations including alternate paternity or maternity (e.g., with assisted reproduction) or undisclosed adoption could also be explored.

Family planning

  • The optimal time for determination of genetic risk and discussion of the availability of prenatal testing is before pregnancy.
  • It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to young adults who are affected.

DNA banking is the storage of DNA (typically extracted from white blood cells) for possible future use. Because it is likely that testing methodology and our understanding of genes, allelic variants, and diseases will improve in the future, consideration should be given to banking DNA of affected individuals.

Prenatal Testing and Preimplantation Genetic Diagnosis

Once the SCRAP pathogenic variant has been identified in the family, prenatal testing for a pregnancy at increased risk and preimplantation genetic diagnosis for Floating-Harbor syndrome are possible.

Resources

GeneReviews staff has selected the following disease-specific and/or umbrella support organizations and/or registries for the benefit of individuals with this disorder and their families. GeneReviews is not responsible for the information provided by other organizations. For information on selection criteria, click here.

  • Human Growth Foundation (HGF)
    997 Glen Cove Avenue
    Suite 5
    Glen Head NY 11545
    Phone: 800-451-6434 (toll-free)
    Fax: 516-671-4055
    Email: hgf1@hgfound.org
  • MAGIC Foundation
    4200 Cantera Drive #106
    Warrenville IL 60555
    Phone: 800-362-4423 (Toll-free Parent Help Line); 630-836-8200
    Fax: 630-836-8181
    Email: contactus@magicfoundation.org

Molecular Genetics

Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.

Table A.

Floating-Harbor Syndrome: Genes and Databases

GeneChromosome LocusProteinLocus-Specific DatabasesHGMDClinVar
SRCAP16p11​.2Helicase SRCAPSRCAP @ LOVDSRCAPSRCAP

Data are compiled from the following standard references: gene from HGNC; chromosome locus from OMIM; protein from UniProt. For a description of databases (Locus Specific, HGMD, ClinVar) to which links are provided, click here.

Table B.

OMIM Entries for Floating-Harbor Syndrome (View All in OMIM)

136140FLOATING-HARBOR SYNDROME; FLHS
611421SNF2-RELATED CBP ACTIVATOR PROTEIN; SRCAP

Gene structure. SRCAP encodes the core catalytic component of the multiprotein chromatin-remodeling SRCAP complex (NM_006662.2). SRCAP is 154 kb in length and comprises 34 exons; exons 1 and 2 are noncoding. For a detailed summary of gene and protein information, see Table A, Gene.

Pathogenic variants. In 13 individuals with FHS reported by Hood et al [2012] all SRCAP pathogenic variants were observed in exon 34. All pathogenic variants (frameshift or nonsense) predict a truncated protein and are clustered between codons 2,407 and 2,517. The two observed recurrent pathogenic variants are described in Table 2 [Hood et al 2012].

Table 2.

Selected SRCAP Pathogenic Variants

DNA Nucleotide ChangeProtein Amino Acid ChangeReference Sequences
c.7303C>Tp.Arg2435TerNM_006662​.2
NP_006653​.2
c.7330C>Tp.Arg2444Ter

Note on variant classification: Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.

Note on nomenclature: GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen​.hgvs.org). See Quick Reference for an explanation of nomenclature.

Normal gene product. Helicase SRCAP, a 400-kd nuclear protein of 3230 amino acids, mediates different intracellular signaling pathways as well as chromatin remodeling. The encoded protein is an ATPase that is necessary for the incorporation of the histone variant H2A.Z into nucleosomes. It is an interacting partner of CREB binding protein (CREBBP, also known as CBP). SRCAP is a potent coactivator for CREB and CBP-mediated transcription. It also functions as a transcriptional activator in Notch-mediated and steroid receptor-mediated transcription.

Abnormal gene product. Germline variants in SRCAP associated with FHS may lead to a gene product with abolished transactivation function located in the 655-residue C-terminal fragment. These pathogenic variants may result in a dominant-negative disease mechanism.

References

Literature Cited

  • Hood RL, Lines MA, Nikkel SM, Schwartzentruber J, Beaulieu C, Nowaczyk MJ, Allanson J, Kim CA, Wieczorek D, Moilanen JS, Lacombe D, Gillessen-Kaesbach G, Whiteford ML, Quaio CR, Gomy I, Bertola DR, Albrecht B, Platzer K, McGillivray G, Zou R, McLeod DR, Chudley AE, Chodirker BN, Marcadier J., FORGE Canada Consortium. Majewski J, Bulman DE, White SM, Boycott KM. Mutations in SRCAP, encoding SNF2-related CREBBP activator protein, cause Floating-Harbor syndrome. Am J Hum Genet. 2012;90:308–13. [PMC free article: PMC3276662] [PubMed: 22265015]
  • Le Goff C, Mahaut C, Bottani A, Doray B, Goldenberg A, Moncla A, Odent S, Nitschke P, Munnich A, Faivre L, Cormier-Daire V. Not all Floating-Harbor syndrome cases are due to mutations in exon 34 of SRCAP. Hum Mutat. 2013;34:88–92. [PubMed: 22965468]

Chapter Notes

Revision History

  • 24 January 2013 (cd) Revision: prenatal testing available clinically
  • 29 November 2012 (me) Review posted live
  • 26 June 2012 (mjmn) Original submission
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