Smith-Fineman-Myers syndrome

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Smith-Fineman-Myers syndrome

Definition

Smith-Fineman-Myers syndrome (SFMS) is a rare and severe type of X-linked inherited mental retardation.

Description

Smith-Fineman-Myers syndrome is also known as Smith-Fineman-Myers type mental retardation and Smith-Fineman-Myers type X-linked mental retardation. SFMS results in severe mental retardation along with characteristic facial features and skeletal differences.

Genetic profile

Smith-Fineman-Myers syndrome is an X-linked disease. X-linked diseases map to the human X chromosome, a sex chromosome. Females have two X chromosomes , whereas males have one X chromosome and one Y chromosome. Because males have only one X chromosome, they require only one copy of an abnormal X-linked gene to display disease. Because females have two X chromosomes, the effect of one X-linked recessive disease gene is masked by the disease gene's normal counterpart on her other X chromosome.

In classic X-linked inheritance males are affected, presenting full clinical symptoms of the disease. Females are not affected. Affected fathers can never pass X-linked diseases to their sons. However, affected fathers always pass X-linked disease genes to their daughters. Females who inherit the faulty gene but do not show the disease are known as carriers. Female carriers of SFMS have a 50% chance to pass the disease-causing gene to each of their children. Each of a female carrier's sons has a 50% chance to display the symptoms of SFMS. None of a female carrier's daughters would display symptoms of SFMS.

Some patients with SFMS have been found to have a mutation in the ATRX gene, on the X chromosome at a location designated as Xq13. ATRX is also the disease gene for several other forms of X-linked mental retardation. Mutations in ATRX are associated with X-linked Alpha-thalassemia/mental retardation syndrome, Carpenter syndrome , Juberg-Marsidi syndrome, and X-linked mental retardation with spastic paraplegia. It is possible that some patients with SFMS have X-linked Alpha-thalassemia/mental retardation syndrome without the hemoglobin H effects that lead to Alpha-thalassemia in the traditionally recognized disease.

Demographics

SFMS affects only males and is very rare. As of early 2001, only 12 cases have been reported in the medical literature. SFMS has been reported in brothers of affected boys.

Signs and symptoms

SFMS visibly affects the skeletal and nervous systems and results in an unusual facial appearance. The genitals may also show effects ranging from mild (e.g. undescended testes) to severe (leading to female gender assignment).

Skeletal features

Boys with SFMS have short stature and a thin body build. Their heads are small and may also be unusually shaped. Scoliosis and chest abnormalities have been reported to occur with SFMS. X rays may show that their bones have characteristics of the bones of people younger than they are. Hands are often short with unusual palm creases and short, unusually shaped fingers. Fingernails may be abnormal. Foot abnormalities and shortened or fused toes have also been reported.

Neurological features

Boys with SFMS exhibit severe mental retardation. Restlessness, behavior problems, seizures, and severe delay in language development are common. Boys with SFMS may be self-absorbed with reduced ability to socialize with others. Affected boys show reduced muscle tone as infants and young children. Later, muscle tone and reflexes are abnormally increased causing spasticity.

Boys with SFMS may display cortical atrophy, or degeneration of the brain's outer layer, on brain imaging studies. Cortical atrophy is commonly found in older unaffected people. When cortical atrophy is found in younger people it is typically due to a serious brain injury. Brain biopsies of two patients with SFMS have been normal.

Facial features

SFMS is associated with unusual facial features including a large mouth with a drooping lower lip, prominent upper jaw and front teeth, and an underdeveloped chin. Cleft palate has been reported in one set of affected twins. Eyes are widely spaced with drooping eyelids. Skin may be lightly pigmented with multiple freckles.

Diagnosis

Assessment for any type of mental retardation should include a detailed family history and thorough physical exam. Brain and skeletal imaging through CT scans or x rays may be helpful. A chromosome study and certain other genetic and biochemical tests help to rule out other possible causes of mental retardation.

Diagnosis of SFMS has traditionally been based on the visible and measurable symptoms of the disease. Until 2000, SFMS was not known to be associated with any particular gene. As of 2001, scientists do not yet know if other genes may be involved in some cases of this rare disease. Genetic analysis of the ATRX gene may, however, prove to be helpful in diagnosis of SFMS.

Treatment and management

Treatment for SFMS is based on the symptoms each individual displays. Seizures are controlled with anticonvulsants. Medications and behavioral modification routines may help to control behavioral problems.

Prognosis

Retardation is severe, but it does not seem to get worse with age. Lifespan does not appear to be shortened.

Resources

BOOKS

Carlson, Hannah, et al. I Have a Friend Who Has Mental Retardation. Madison, CT: Bick Publishing House, 1997.

Shannon, Joyce Brennfleck. Mental Retardation SourceBook: Basic Consumer Health Information about Mental Retardation and Its Causes, Including Down Syndrome, Fetal Alcohol Syndrome, Fragile X Syndrome. Detroit: Omnigraphics, Inc., 1999.

ORGANIZATIONS

American Association on Mental Retardation (AAMR). 444 North Capitol Street NW, Suite 846, Washington, DC 20001-1512. (800) 424-3688. <http://www.aamr.org>.

Arc of the United States (formerly Association for Retarded Citizens of the US). 500 East Border St., Suite 300, Arlington, TX 76010. (817) 261-6003. <http://thearc.org>.