Floating-Harbor Syndrome Treated With Recombinant Human Growth Hormone: A Case Report and Literature Review

Introduction: We aimed to summarize the clinical characteristics of Floating-Harbor syndrome (FHS) and the effect of recombinant human growth hormone (rhGH) to increase height.Methods: The clinical manifestations, gene sequencing results, treatment, and regression of one child with FHS were reported at the Department of Pediatrics, General Hospital of Tianjin Medical University, in July 2020. PubMed was searched using the keyword “Floating-Harbor Syndrome” up to March 2021 to obtain clinical information on children with FHS for review.Results: The child, who was a male aged 6 years and 9 months, presented to the clinic with main complaints of delayed language development since childhood and a short stature for 4 years. The child's short stature, peculiar facial features, delayed language development, and delayed bone development were considered alongside genetic testing and Sanger sequencing to verify the results. A heterozygous mutation (c.7401delC; p.Ile2468Phefs*7) was identified in exon 34 of the SRCAP gene, which was a frameshift mutation, and Sanger verification showed that neither parent had this mutation. The child was administered subcutaneous injection of rhGH (0.13 U/kg/day) and was followed up regularly. At the time of writing, the child had been treated for 6 months and was 7 years and 3 months old with a height of 106.3 cm (−3.69 SDS), which was a height increase of 6.3 cm. The patient did not complain of discomfort during treatment and presented normal laboratory tests results. Twenty-two children with FHS treated with rhGH were included in the literature review, and most of these patients demonstrated an increase in height SDS without adverse effects.Conclusion: Short stature, delayed skeletal maturation, impaired language expression, intellectual deficits, and peculiar facial features are the main clinical features of FHS. rhGH can be used as a treatment to increase height in patients with FHS, but its effectiveness and safety still need to be monitored in larger sample sizes over longer periods of time.

The ATPase SRCAP is associated with the mitotic apparatus, uncovering novel molecular aspects of Floating-Harbor syndrome

Background A variety of human genetic diseases is known to be caused by mutations in genes encoding chromatin factors and epigenetic regulators, such as DNA or histone modifying enzymes and members of ATP-dependent chromatin remodeling complexes. Floating-Harbor syndrome is a rare genetic disease affecting human development caused by dominant truncating mutations in the SRCAP gene, which encodes the ATPase SRCAP, the core catalytic subunit of the homonymous chromatin-remodeling complex. The main function of the SRCAP complex is to promote the exchange of histone H2A with the H2A.Z variant. According to the canonical role played by the SRCAP protein in epigenetic regulation, the Floating-Harbor syndrome is thought to be a consequence of chromatin perturbations. However, additional potential physiological functions of SRCAP have not been sufficiently explored. Results We combined cell biology, reverse genetics, and biochemical approaches to study the subcellular localization of the SRCAP protein and assess its involvement in cell cycle progression in HeLa cells. Surprisingly, we found that SRCAP associates with components of the mitotic apparatus (centrosomes, spindle, midbody), interacts with a plethora of cytokinesis regulators, and positively regulates their recruitment to the midbody. Remarkably, SRCAP depletion perturbs both mitosis and cytokinesis. Similarly, DOM-A, the functional SRCAP orthologue in Drosophila melanogaster, is found at centrosomes and the midbody in Drosophila cells, and its depletion similarly affects both mitosis and cytokinesis. Conclusions Our findings provide first evidence suggesting that SRCAP plays previously undetected and evolutionarily conserved roles in cell division, independent of its functions in chromatin regulation. SRCAP may participate in two different steps of cell division: by ensuring proper chromosome segregation during mitosis and midbody function during cytokinesis. Moreover, our findings emphasize a surprising scenario whereby alterations in cell division produced by SRCAP mutations may contribute to the onset of Floating-Harbor syndrome.

Novel Findings in Floating-Harbor Syndrome and a Mini-Review of the Literature

Floating-Harbor syndrome (FHS) is a rare autosomal dominant genetic disorder characterized by proportionate short stature with delayed bone maturation, lack of expressive language, and distinctive facial features including a large nose, long eyelashes, deeply set eyes, and triangular face. Mutations in the <i>SRCAP</i> gene cause truncated SNF2-related CREBBP activator protein (SRCAP) and lead to FHS. SRCAP is one of several proteins that act as coactivator for the CREB-binding protein which is associated with Rubinstein-Taybi syndrome (RSTS). This condition likely explains the phenotypic overlap between FHS and RSTS. Herein, we report on a patient with FHS who also had dystrophic toenails, preauricular skin tag, and nasolacrimal duct obstruction which is also defined in patients with RSTS. In summary, the fact that especially nasolacrimal duct obstruction has also been observed in RSTS reinforces the idea that this finding is one of the features of FHS. Assessment of the lacrimal system and examination of skin and nails should be suggested in patients with FHS.

ATPase SRCAP is a new player in cell division, uncovering molecular aspects of Floating-Harbor syndrome

Floating-Harbor syndrome (FHS) is a rare genetic disease affecting human development caused by heterozygous truncating mutations in the Srcap gene, which encodes the ATPase SRCAP, the core catalytic subunit of the homonymous chromatin-remodeling complex. Using a combined approach, we studied the involvement of SRCAP protein in cell cycle progression in HeLa cells. In addition to the canonical localization in interphase nuclei, both SRCAP and its Drosophila orthologue DOMINO-A localized to the mitotic apparatus after nuclear envelope breakdown. Moreover, SRCAP and DOMINO-A depletion impaired mitosis and cytokinesis in human and Drosophila cells, respectively. Importantly, SRCAP interacted with several cytokinesis regulators at telophase, strongly supporting a direct role in cytokinesis, independent of its chromatin remodeling functions. Our results provide clues about previously undetected, evolutionarily conserved roles of SRCAP in ensuring proper mitosis and cytokinesis. We propose that perturbations in cell division contribute to the onset of developmental defects characteristic of FHS.SummarySignificance statementSrcap is the causative gene of the rare Floating Harbor syndrome (FHS). It encodes the ATPase SRCAP, the core catalytic subunit of the homonymous multiprotein chromatin-remodeling complex in humans, which promotes the exchange of canonical histone H2A with the H2A.Z variant. According to the current view on SRCAP protein functions, FHS is caused by chromatin remodeling defects. Our findings suggest that, in addition to the established function as epigenetic regulator, SRCAP plays previously undetected and evolutionarily conserved roles in cell division. Hence, we propose that perturbations in cell division produced by SRCAP mutations are important causative factors co-occurring at the onset of FHS.