Floating-Harbor syndrome is a disorder involving short stature, slowing of the mineralization of the bones (bone age), delayed speech development, and characteristic facial features. It is also a Global Specific Developmental Delay that affects children in various ways.
In 1973, Pelletier and Feingold described a young male who was seen at the Boston Floating Hospital with short stature, delayed speech and unusually triangular facial appearance. A further report of a similar case was published by Leisti et al. who had seen their patient at the Harbor General Hospital, Torrance, California. they suggested the term Floating Harbor Syndrome.
There are around 100 recognised individuals with a diagnosis of Floating Harbor Syndrome worldwide, including the UK, Australia, Canada, USA, Italy and many more.
Information relating to this syndrome has until recently been very limited. More data is being made available and more easily accessible on the Internet. Please keep checking back for updates as we get them. There are a whole range of areas of physical and cognitive delays associated with Floating Harbor Syndrome and we try to cover as much as possible throughout this site. It is not a case of one size fits all, and you may recognize some symptoms and not others.
Everyone is different, therefore parents should talk to their children’s physician and medical team about their specific case, associated symptoms and overall prognosis. It is vital however that the FHS child is monitored closely by specialized professionals throughout childhood, and parents are given every opportunity to share the experiences of the child from their perception. Working together is vital for a positive outcome.
Several factors including the small number of identified cases, the lack of large clinical studies, and the possibility of other genes influencing the disorder prevent physicians from developing a complete picture of associated symptoms and prognosis, therefore, it is important to note that affected individuals may not have all of the symptoms discussed below. In some cases, delayed growth may occur before birth (prenatal growth retardation) resulting in low birth weight. Typically, growth deficiencies become apparent during the first year of life. Affected children may be below average height for their age (short stature), and among the shortest 5 percent of their age group.
Children with FHS may exhibit behavioural abnormalities including hyperactivity, impulsivity, short attention span, aggression, anxiousness, however some children can also be placid, disinterested and loving to be around.
Some of the obsessive behaviours such as repeated skin picking and destructive moods are also reported.
A common concern for care givers is FHS individuals have a high pain threshold. This is consistent with sensory disorders.
Education for children with FHS is one of the big concerns for parents and the information provided here as a guidance for teachers, should be adhered to as much as possible; this is aimed to help the child have a positive learning experience. Click Here to view.
Speech and language deficits are common in children with FHS. Expressive language deficits are most common and often most severely affected. Expressive language is the ability of a person to ‘output’ language or how people express themselves such as through speech or writing. It also encompasses the use of gestures and facial expressions. Some affected children also have receptive language deficits, in which they are unable to understand words and gestures. Affected individuals may have difficulty speaking (dysarthria) and exhibit a distinct, high-pitched nasally voice. In some cases, speech may be absent. Children may be described as having verbal dyspraxia, which refers to the difficulty or inability to coordinate the precise movements required to produce clear speech despite the absence of damage to the nerves or muscles. The severity of expressive and receptive language abnormalities can vary widely.
Intellectual disability that is typically mild to moderate in degree has been reported. Learning disabilities are common as well.
This can affect their comprehension therefore constant repetition is required to reinforce what they learn. Their development of motor skills, such as sitting and crawling, can be similar to that of other children their age.
In addition to growth deficiencies, children with FHS have a delay in bone aging in the first decade of life, which means that the rate of growth and calcification of the bones is slower than normal.
Infants and children with FHS have distinctive facial features including a triangularly-shaped face; low-set ears; deep-set eyes with abnormally long eyelashes; thin lips; a broad, linear mouth; a prominent, triangular-shaped nose that is narrow at the root and broadens at the base; the bottom of the sheet of cartilage and bone (nasal septum) that separates the right and left nostrils (columella) may be low-hanging; the nostrils are large; and the groove that runs from the nose to the upper lip (philtrum) is short. These facial characteristics are the most distinctive features of FHS. Although they may change as an affected individual ages, the key features remain constant.
It has been recorded that some children with a diagnosis of Floating Harbor Syndrome also have Isodicentric chromosome 15 syndrome, which is a developmental disorder with a broad spectrum of features. The signs and symptoms vary among affected individuals.
Poor muscle tone is commonly seen in individuals with isodicentric chromosome 15 syndrome and contributes to delayed development and impairment of motor skills, including sitting and walking.
Affected individuals exhibit various skeletal malformations including short fingers and toes (brachydactyly); broad fingertips that give the appearance of clubbing; short, broad thumbs; and prominent joints. The pinkies may be fixed or ‘locked’ in a bent position (clinodactyly). Some individuals may have abnormalities of the collarbones (clavicles) including underdevelopment (hypoplasia) of the collarbone or the development of a ‘false joint’ (pseudoarthrosis). A false joint is a bony structure that usually develops at the site of a poorly united fracture that allows abnormal movement of the affected bones.
Dental abnormalities are also common with FHS and it is of extreme importance that you should discuss your child’s background before any treatment starts. Dental anomalies may also occur including extra (supernumerary) teeth, delayed loss of primary (“baby”) teeth, abnormally small teeth (microdontia), and malocclusion, a condition in which the upper teeth are improperly positioned in relation to the lower teeth.
Additional symptoms have been reported in individuals with FHS including short bones in the hands (metacarpals); the presence of 11 pairs of ribs instead of 12; malformed (dysplastic) hips; abnormal curvature of the spine (kyphoscoliosis); seizures; backflow or leakage of the contents of the stomach into the oesophagus (gastroesophageal reflux); farsightedness (hyperopia); crossed eyes (strabismus); recurrent middle ear infections (otitis media); and conductive hearing loss. Conductive hearing loss occurs when there is impaired transmission of sound from the outer or middle ear to the inner ear. The individual will shout and talk loudly. Normal hearing tests are not appropriate to pick up the affected areas, again, inform your physician of the above impaired transmission of sound. In some cases, affected individuals may exhibit kidney abnormalities such as cysts on the kidneys or swelling (distension) of the kidneys due to the abnormal accumulation of urine (hydronephrosis). Hydronephrosis develops because of blockage within the urinary tract that prevents urine from being evacuated through the bladder. In some cases, there may be absence of the kidneys (agenesis).
In some cases, the onset of puberty may occur earlier than normal(Precocious puberty). Males may have undescended testicles (cryptorchidism) and hypospadias, a condition in which the tube that is connected to the bladder and discharges urine from the body (urethra) opens on the underside of the penis instead of the tip.
Other conditions that have been reported in individuals with FHS include Coeliac disease, congenital heart defects, mild underactivity of the thyroid (hypothyroidism), and, in adulthood, high blood pressure (hypertension).
Floating-Harbor syndrome is caused by a mutation in the SRCAP gene. Genes provide instructions for creating proteins that play a critical role in many functions of the body. When a mutation of a gene occurs, the protein product may be faulty, inefficient, or absent. Depending upon the functions of the particular protein, this can affect many organ systems of the body.
Investigators have determined that the SRCAP gene is located on the short arm (p) of chromosome 16 (16p11). Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered.
In FHS, mutations in the SRCAP gene often occur as a new (sporadic or de novo) mutation, which means that in nearly all cases the gene mutation has occurred at the time of the formation of the egg or sperm for that child only, and no other family member will be affected. There are no silent carriers of FHS (i.e. if one carries a mutation in SRCAP, he/she will show signs of FHS).
Although most cases are due to sporadic mutations, dominant inheritance (where a trait is transmitted from either an affected mother or father to a child) has been documented in a few families. Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother. Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy. The risk is the same for males and females.
The SRCAP gene creates (encodes) a protein that has several functions in the body. This protein is a cofactor (i.e. a substance required for a protein’s biological activity) for the CREB-binding protein (CREBBP). Mutations in the gene that produces CREB-binding protein cause Rubinstein-Taybi syndrome, a rare disorder with many overlapping symptoms to FHS.
We constantly strive to update information as and when it is available, therefore if you have anything to add, please contact us.