Acrocallosal syndrome is a rare congenital disorder in which the individual has absence or only partial formation of the corpus callosum. This is accompanied by skull and facial malformations, and some degree of finger or toe malformations. Individuals may display motor and mental retardation. The cause of this genetic disorder is unknown, and the severity of the symptoms vary by individual.
Acrocallosal syndrome was first described by Schinzel in 1979, and also may be referred to as Schinzel acrocallosal syndrome. The term acrocallosal refers to the involvement of the acra (fingers and toes) and the corpus callosum, the thick band of fibers joining the hemispheres of the brain. Reported in both males and females, the cause of the disorder is unknown. The major characteristic of the syndrome is the incomplete formation (hypoplasia) or absence (agenesis) of the corpus callosum. Facial appearance is typically similar among affected people. This includes a prominent forehead, an abnormal increase in the distance between the eyes (hypertelorism), and a large head (macrocephaly). Individuals have a degree of webbing or fusion (syndactyly), or duplication (polydactyly) of the fingers and toes. Occasionally, those affected may have a short upper lip, cleft palate, cysts that occur within the cranium (intracranial), hernias, or may develop seizure disorders. Less frequently, affected children have congenital heart defects , internal organ (visceral) or kidney (renal) abnormalities.
Moderate to severe mental retardation is reported with acrocallosal syndrome. Individuals usually display some form of poor muscle tone (hypotonia), and there may be a delay or absence of motor activities, walking, and talking. There is great variation of functioning and symptoms with this disorder, ranging from normal development to severe mental and motor retardation.
The cause of acrocallosal syndrome is unknown. There are sporadic, or random, cases, and reports of multiple cases within families. Studies involving affected families have suggested an autosomal recessive pattern of inheritance . This means that both parents carry the altered form of the gene and the affected child inherited both copies. Following this pattern, each child born will have a 25% risk of being affected.
To help determine which chromosome or gene location causes the syndrome, acrocallosal syndrome has been compared with similar disorders. One condition that presents similar symptoms and has a known genetic cause is Greig cephalopolysyndactyly syndrome . However, there is no genetic similarity between the two conditions. To date, no specific genetic cause for acrocallosal syndrome is known, and the disorder can only be identified by clinical symptoms.
Acrocallosal syndrome is extremely rare. Reports of this disorder may occur within family lines, or randomly. It affects both males and females. There are some reports of webbing of the fingers or toes (syndactyly) and relatedness (consanguinity) of the parents of affected children. However, affected children may also have unrelated, healthy parents and unaffected siblings.
Signs and symptoms
At birth, those with acrocallosal syndrome present the characteristic pattern of facial and limb malformations. Limb appearance ranges from minor webbing between the fingers or toes to near duplication of the hands or feet. Forehead prominence, increased distance between the eyes, and an enlarged head are the main features of facial appearance. X ray tests will reveal the absence or incomplete formation of the corpus callosum and the presence of any cysts within the cranium. The infant will usually display reduced muscle tone (hypotonia). This may lead to a drooling condition or feeding difficulties. Hypotonia can also contribute to a delay in growth and motor skills. Severe hypotonia is usually associated with a form of mental retardation.
Progress and functioning during the first year of life is dependent upon the severity of the symptoms. There has been a wide range of individual variation reported, and the degree to which symptoms affect each child may differ. Some children develop normally and will walk and talk within normal age limits, while others may experience a delay or absence of certain motor activities. Mental retardation may be moderate or severe. Some children may develop seizure disorders. The degree and progression of mental retardation also varies by individual.
The diagnosis of acrocallosal syndrome is based initially on the distinct pattern of facial and limb malformations. Computed tomography (CT), or a similar radiographic procedure of the head reveals the absence of the corpus callosum. Hand and foot x rays can be taken to confirm finger or toe abnormalities, and will determine the extent of fusion, webbing, or duplication of the digits (fingers or toes).
Prenatal diagnosis may not be possible due to the variability of the condition. However, prenatal ultrasound can detect duplication of the digits (polydactyly) and cerebral malformations. This may be especially informative for a woman who already has an affected child and has a 25% risk of having another affected child.
Treatment and management
Beginning in infancy, physical therapy may assist in the development of motor skills and muscle tone. Surgery to remove extra fingers and release fused fingers may improve movement and grasp, though the muscle tone may remain poor. Surgery to separate or remove affected toes may assist in walking and the comfort of footwear. Anti-epileptic therapy should be considered if a seizure disorder develops. Special education may be required, depending on the level of mental impairment.
At present, there are no preventative measures for acrocallosal syndrome, and the severity of symptoms and outcomes varies by individual. It has been found that the lifestyle of an individual with acrocallosal syndrome is dependent upon the degree of mental retardation and reduced muscle tone, rather than the extent of facial and limb malformations.
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Agenesis of the Corpus Callosum (ACC) Network. Merrill Hall, University of Maine, Room 18, 5749, Orono, ME 04469-5749. (207) 581-3119. [email protected]
FACES: The National Craniofacial Association.<http://www.faces-cranio.org>.
Maureen Teresa Mahon, BSc, MFS