Smith magensis syndrome
Once the genetic anomaly deletion or mutation is identified in a proband, both parents should be tested to confirm a de novo event [ 15 ]. Affected individuals may also exhibit absence agenesis of secondary permanent teeth, particularly premolars, and taurodauntism, a condition characterized by enlargement of the pulp chambers and reduction of the roots of teeth; open bite posture with large tongue macroglossia and history of bruxism teeth grinding are also common.
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Failure to thrive is defined as the failure to grow and gain weight at a rate that would be expected based upon age and gender. Their walk may be somewhat unstable but they do not present with true ataxia. Experts also say some genetic tests are not sensitive enough to pick up chromosomal deletions, especially if the deleted portions are small. To determine the precise breakpoint, a more sensitive test known as fluorescent in situ hybridization FISH may be necessary. Conductive hearing loss develops when sound waves are inappropriately conducted through the external or middle ear to the inner ear, resulting in decreased sensitivity to sound. A chromosome abnormality is noted when a difference is found between the DNA samples. Affected children tend to be excitable and easily distracted. Some individuals also have ear abnormalities that lead to hearing loss and also possible vision difficulties. Peripheral neuropathy, which is a general term for any disorder of the peripheral nervous system, may also occur.
But, they say, there's no effective medication for people with SMS. In two families reported in the medical literature, SMS occurred because of germline mosaicism. About 90 percent of cases of SMS are caused by a deletion of a portion of chromosome SMS is typically not inherited.
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The mouth curves downwards and the upper lip curves outwards, due to a fleshy philtrum. Other genes within the deleted segment may also play a role in variable features in the syndrome, but it is not fully understood how significant a role they play in the development of SMS. Refraction abnormalities are often found and frequently linked to hypermetropia. Although this region contains multiple genes, recently researchers discovered that the loss of one particular gene the retinoic acid induced 1 or RAI1 is responsible for most of the characteristic features of this condition. The phenotype may vary among subjects presenting identical deletions or mutations, and even between monozygotic twins with SMS. During the neonatal period, hypotonia and difficulty breast-feeding are often observed. A translocation is balanced if pieces of two or more chromosomes break off and trade places, creating an altered but balanced set of chromosomes. About 90 percent of cases of SMS are caused by a deletion of a portion of chromosome There is also a mild brachycephaly. If there's any change in a routine, that often sets off tantrums. Frequent sinus infections sinusitis are also common. Oral sensorimotor dysfunction, in which affected individuals have difficulties controlling the lips, tongue and jaw muscles, may also develop and can cause tongue protrusion and frequent drooling.
From an ophthalmological point of view, iris anomalies heterochromia or hamartomasstrabismus, and microcornea have been reported. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y.
Duplications in the 17p The loss of other genes in the deleted region may help explain why the features of Smith-Magenis syndrome vary among affected individuals. Diagnosis A diagnosis of Smith-Magenis syndrome is based upon identification of characteristic symptoms, a detailed patient and family history, a thorough clinical evaluation and a variety of specialized genetic tests.
Chronic constipation is also a frequent complication.
Micrognathia — readily observed during the first years of life — reverses over time, tending towards prognathism characterized by a wide, square-shaped face Fig.
based on 45 review