Floating-Harbor Syndrome

A number sign (#) is used with this entry because of evidence that Floating-Harbor syndrome (FLHS) is caused by heterozygous mutation in the SRCAP gene (611421) on chromosome 16p11.

Description

Floating-Harbor syndrome is a rare genetic disorder characterized by proportionate short stature, delayed bone age, delayed speech development, and typical facial features. The face is triangular with deep-set eyes, long eyelashes, bulbous nose, wide columella, short philtrum, and thin lips (Lacombe et al., 1995).

Rubinstein-Taybi syndrome (see 180849), which shows phenotypic overlap with Floating-Harbor syndrome, is caused by mutation in the CREBBP gene (600140), for which SRCAP is a coactivator.

Clinical Features

Robinson et al. (1988) used the designation Floating-Harbor syndrome for a syndrome that was first described by Pelletier and Feingold (1973) in a boy seen at the Boston Floating Hospital and by Leisti et al. (1975) in a patient at the Harbor General Hospital in Torrance, California. The syndrome is characterized by a triad of short stature with significantly delayed bone age; expressive language delay, usually in the presence of normal motor development; and a triangular face with a prominent nose and deep-set eyes.

Feingold (2006) provided a 32-year clinical follow-up of the first patient with Floating-Harbor syndrome reported by Pelletier and Feingold (1973). At 37 years of age, the patient was in good health except for arthritis and hypertension. His facial appearance remained fairly characteristic with low hairline, broad nasal tip, short nasal labial distance, depressed columella, thin lips, and posteriorly positioned ears. His stature remained short, and he had mild to moderate mental retardation. Feingold (2006) emphasized that the correct diagnosis of the syndrome should be based on the characteristic facial features.

Patton et al. (1991) reviewed 7 families, each with a single affected patient. Two of the 7 were male. The chromosome studies were normal. Only one of the cases was the product of a consanguineous marriage, a third-cousin Iranian union. No information on parental age was provided. It is possible that this represents a new dominant mutation.

Chudley and Moroz (1991) reported the case of a 17-year-old girl with celiac disease and features consistent with Floating-Harbor syndrome. Celiac disease had been reported in 1 of 6 previously reported cases. Majewski and Lenard (1991) reported the presumed seventh case.

Lacombe et al. (1995) reported a case and reviewed 16 cases from the literature. The father was 54 years old and the mother 41. Growth and speech development were delayed throughout infancy, although motor development was normal. Proportionate short stature and characteristic face, which was triangular with broad and bulbous nose with a prominent nasal bridge, large nares, and a wide columella below the level of the nares, were described. Other facial features included glabella angioma, short philtrum, and thin upper and lower lips. There was brachyphalangy and bilateral fifth finger clinodactyly. At the age of 7 years and 9 months, she had the bone age of a 3-year-old. Dominant inheritance was suggested by the fact that the patient's mother had short stature (138 cm), mild mental retardation, and facial appearance resembling her daughter with a bulbous nose, thin lips, and brachyphalangy of hands and feet.

Smeets et al. (1996) reported a girl with typical manifestations of the syndrome. The authors noted that marked speech delay and odd and hyperkinetic behavior may also be found in small children with Shprintzen velocardiofacial syndrome (192430).

Ala-Mello and Peippo (1996) described a 6-year-old boy of Finnish origin who, in addition to typical manifestations of the syndrome, had unusual high-pitched voice and supernumerary upper incisor, 2 features that had not been reported in other patients. Abnormal high titers of gliadin antibodies suggesting celiac disease were also found in this boy. Celiac disease had been described in at least 3 other patients with Floating-Harbor syndrome. Ala-Mello and Peippo (1996) suggested that all patients with this syndrome should be examined for celiac disease.

Ala-Mello and Peippo (2004) reported follow-up on the Finnish patient they reported in 1996. Reexamination at age 14 years showed classic facial features of the syndrome, with a more pronounced nose, prognathism, and hypoplasia of the maxilla. He had also had recurrent middle ear infections. Growth rate had accelerated (height at -0.7 SD), hands and feet were small (less than third percentile), and his pubertal stage was Tanner P3G3 with normal testicular size and normal bone age. His high-pitched voice described earlier was no longer so pronounced. Reticulin and gliadin antibody titers were normal.

Davalos et al. (1996) described a 6-year-old Mexican girl whose clinical picture (short stature with delayed bone age, language difficulties, and triangular face with prominent nose) was compatible with the diagnosis of Floating-Harbor syndrome. Neuropsychologic evaluation disclosed mild mental retardation, constructive apraxia, and comprehensive and expressive language impairment. Sixteen previously described patients were reviewed.

Midro et al. (1997) reported this syndrome in a 9-year-old girl who showed short stature, delayed bone age, mild mental retardation, speech problems, and specific craniofacial features.

A girl with Floating-Harbor syndrome reported by Hersh et al. (1998) showed trigonocephaly due to metopic suture synostosis, preauricular pit, hypoplastic thumb, subluxated radial head, and Sprengel deformity. From a review of other cases they suggested that trigonocephaly may be an important craniofacial manifestation recognizable in infancy but becoming less noticeable later when the face develops a triangular shape, accentuated by a broad and bulbous nose.

Wieczorek et al. (2001) reported 2 female patients, aged 11 and 8 years, with clinical findings consistent with Floating-Harbor syndrome. The first patient presented with characteristic facial features (large nose with wide columella and hypoplastic alae nasi, short philtrum, and prominent chin), brachydactyly, broad thumbs, and delayed speech development, but less pronounced short stature than previously reported. The second patient presented with short stature, characteristic facial features, brachydactyly, and delayed speech as well as mental development; she was successfully treated with growth hormone. Wieczorek et al. (2001) commented on the facial similarity of their 2 patients with the patient reported by Houlston et al. (1994) and reproduced pictures for comparison. They also commented on a similarity of the metacarpal phalangeal pattern profiles (MCPP) in their patients and in previously reported patients.

Penaloza et al. (2003) suggested Floating-Harbor syndrome as the diagnosis in a 2-year-old boy with short stature, retarded speech development, delayed bone age, a bulbous nose, wide columella, and thin lips. Intestinal biopsy revealed villous atrophy compatible with celiac disease. The mother was thought to have minor phenotypic characteristics, supporting the possibility of dominant inheritance. She had a triangular face, deep-set eyes, a wide columella, and thin lips.

Ioan and Fryns (2003) described 2 sisters with clinical histories and physical findings most compatible with the diagnosis of Floating-Harbor syndrome. Family data favored autosomal recessive inheritance, although germinal mosaicism for an autosomal dominant mutation could not be excluded. Both sisters had microcephaly and developmental delay, with expressive language being severely retarded. Both were of short stature and had distinct craniofacial appearance: triangular face with deeply-set eyes, large and bulbous nose with wide columella, short philtrum, high-arched palate, and low-set ears.

Wiltshire et al. (2005) reported a patient with Floating-Harbor syndrome complicated by a tethered spinal cord. She had typical facies, delayed bone age, delay in expressive speech, and short stature treated with growth hormone. At age 6 years, she developed daytime enuresis, gait disturbance, hyperreflexia of the lower limbs, and extensor plantar responses. Spinal MRI showed tethered cord with a small lipoma. Surgical repair was successful. Wiltshire et al. (2005) suggested that increased growth velocity associated with growth hormone therapy may have unmasked the tethered cord in this patient.

Karaer et al. (2006) reported an 8-year-old Turkish girl with microcephaly, normal psychomotor development with speech delay and a high-pitched voice, triangular face with temporal narrowing and posteriorly angulated ears, upslanting palpebral fissures, deep-set eyes with long eyelashes, large and protruding nose with wide columella and hypoplastic alae nasi, high-arched palate, and supernumerary incisor. She had short stature with delayed bone age, small hands and feet with hypermobile and hyperextensible fingers, and hirsutism, especially on the upper arms and shoulders. Her intellectual abilities were in the average range, but she had hyperactivity disorder and learning disabilities. She had constipation but no evidence of celiac disease. Karaer et al. (2006) stated that this was the first female Turkish patient with Floating-Harbor syndrome.

Paluzzi et al. (2008) reported a woman who was diagnosed at 4.5 years of age with Floating-Harbor syndrome based on dysmorphic facial features involving a prominent nose with broad nares, short upper lip with a wide mouth, and a small jaw, in association with good perceptive language but delayed expressive speech, a petit mal seizure disorder, and short stature with delayed bone age. At 22 years of age, the patient presented with severe headache, vomiting, and neck stiffness and was found to have a ruptured aneurysm of the left internal carotid artery by CT angiography, which was successfully embolized. Fenestration of the distal internal carotid artery was also noted on the angiogram.

White et al. (2010) reported 10 patients with a diagnosis of Floating-Harbor syndrome, including 1 previously studied patient ('patient 5' of Robinson et al., 1988). Serial photographs of the patients demonstrated that the dysmorphic facial features of FLHS are age-related. In infancy and early childhood, deep-set eyes with relatively short palpebral fissures, a triangular configuration to the nasal tip, and a thin upper lip vermilion are seen; however, in later childhood, the classic facial appearance alters substantially, with widening of the palpebral fissures, which makes the eyes appear less deep-set, and increasing prominence of the nasal tip. In addition, bone age data in this study indicated that it is a reliable diagnostic feature under the age of 6 years, but may be normal in otherwise typical patients from 6 years to puberty. White et al. (2010) argued that the disorder of speech and language is more severe than previously recognized, noting that children with FLHS have difficulties with all facets of motor speech production and that language, literacy, and social aspects of communication are severely impaired. Consistent with previous reports, most patients in this study were rated as having borderline normal intellectual function or a mild intellectual disability, and noted as having abnormal hands, albeit with variable features.

Nelson et al. (2009) described a 5-year-old boy with short stature, delayed bone age, expressive language delay, developmental delay, and facial anomalies consistent with Floating-Harbor syndrome, who also developed an intramedullary ganglioglioma extending from T7 to the conus. The authors stated that this was the first report of a tumor associated with FLHS.

In a 9-year-old Turkish girl with Floating-Harbor syndrome who was being evaluated for hearing loss that showed only minimal improvement after the placement of grommets, Hendrickx et al. (2010) performed high-resolution CT of the temporal bone and observed bilateral prominent soft-tissue thickening between the head of the malleus and the anterior wall of the atticus. In addition, on the right, there was fusion of the head of the malleus with the body of the incus, whereas on the left, narrowing of the articulation between malleus and incus was seen. Hendrickx et al. (2010) stated that this was the first reported abnormal middle ear anatomy in a patient with FLHS.

Inheritance

Reports of Floating-Harbor syndrome have suggested autosomal dominant (e.g., Lacombe et al., 1995) or autosomal recessive (e.g., Ioan and Fryns, 2003) inheritance.

White et al. (2010) described a mother-daughter pair, in which the daughter had delayed bone age and facial features that were characteristic of FLHS, whereas the mother had features showing similarity to FLHS. Both had short stature and speech/language difficulties like those of FLHS patients.

Molecular Genetics

Hood et al. (2012) performed exome capture and high-throughput sequencing in 5 unrelated probands with Floating-Harbor syndrome, including 2 patients (patients 9 and 10) previously studied by White et al. (2010), and identified heterozygosity in all 5 probands for 3 truncating variants in the SRCAP gene (611421.0001-611421.0003, respectively). Analysis of SRCAP in an additional 8 probands, including 'patient 8' of White et al. (2010), identified 6 with heterozygosity for 2 of the previously identified mutations, respectively (611421.0001; 611421.0002), as well as 2 with heterozygosity for 2 more frameshift mutations. The mutations were shown to be de novo in all 6 instances in which parental DNA was available, and none were represented in the dbSNP (build 131), 1000 Genomes Project, or NHLBI Exome Variant Server. The authors stated that the phenotype of mutation-positive individuals was concordant with earlier descriptions of FLHS, and that nearly all individuals had short stature and expressive language impairment. However, despite the remarkable similarity among mutations in these patients, all of which were truncating mutations tightly clustered in the last exon of the SRCAP gene, cognitive outcomes ranging from 'normal' to 'significant intellectual disability' were reported, suggesting that genetic modifiers and/or environmental factors might be involved.

By whole-exome sequencing followed by Sanger sequencing, Le Goff et al. (2013) identified heterozygous mutations in the SRCAP gene in 6 of 9 patients with Floating-Harbor syndrome (see, e.g., 611421.0001, 611421.0002, and 611421.0004). There were no major clinical differences between the mutation-positive patients and those in whom no mutation was found. Le Goff et al. (2013) concluded that Floating-Harbor syndrome is a clinically homogeneous but genetically heterogeneous condition, although they noted that partial intragenic deletions or mutations in the introns or promoter region could not be excluded in the mutation-negative patients.

Kehrer et al. (2014) identified a de novo heterozygous truncating mutation in exon 33 of the SRCAP gene (Q2334X; 611421.0005) in a German boy with FLHS. Kehrer et al. (2014) noted that this was the first reported SRCAP mutation that was not in exon 34. Functional studies were not performed.