KBG Syndrome

KBG Syndrome

National Organization for Rare Disorders, Inc.

Important

It is possible that the main title of the report KBG Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.

Synonyms

  • Short Stature, Facial/Skeletal Anomalies-Retardation-Macrodontia

Disorder Subdivisions

  • None

General Discussion

KBG syndrome is a very rare genetic disorder characterized by short stature, moderate to severe degrees of mental retardation, developmental abnormalities of the limbs, bones of the spine (vertebrae), extremities, and/or underdevelopment of the bones of the skeleton. Abnormalities of the head and face (craniofacial dysmorphism) and malformations of the teeth and jaws (dento- skeletal dysplasia) may also be present. The exact cause of KBG syndrome is unknown, but most cases are believed to be autosomal dominant traits with variable degree of penetrance.

Symptoms

Children with KBG syndrome may display characteristic physical abnormalities of the head and face (craniofacial dysmorphism). Fibrous joints (coronal sutures) between certain cranial bones of the skull may close prematurely; as a result, the head may appear unusually broad, short, and/or rounded. Characteristic facial features may include eyes that appear widely spaced (telecanthus) or crossed (strabismus); wide, bushy eyebrows; and/or thin, bow-shaped lips. Characteristic features may also include abnormally large teeth in comparison to the jaws (macrodontia); jagged, crowded, or misaligned teeth; and/or unusually short, flattened, supporting bones or sockets of the jaw (mandible) that house the teeth (alveolar ridges).



A child with KBG syndrome may also be of short stature, have speech and hearing impairments, and/or have mild to severe levels of mental retardation. In some cases, mental retardation may be attributed to a small head in relation to the rest of the body (microcephaly). Affected individuals may also display abnormal bone development (skeletal dysplasia) such as malformations of the bones of the spine (vertebrae); the shortened middle portion of the thigh bones (femoral neck); abnormally developed hip bones (hip dysplasia); and/or shortened, hollow finger bones (metacarpals).



In some cases, associated features may include a sunken, pushed-in appearance of the chest (pectus excavatum or "funnel chest"); webbing or fusion of the middle toes (syndactyly); a single deep crease across the palms of the hands (simian crease); and/or six fingers or toes on one limb (hexadactyly). The number and severity of these symptoms vary widely among affected individuals.

Causes

Most cases of KBG syndrome are thought to be inherited as an autosomal dominant trait with variable degree of penetrance. Human traits, including the classic genetic diseases, are the product of the interaction of two genes, one received from the father and one from 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 regardless of the sex of the resulting child.



Variable or incomplete penetrance means that some individuals who inherit the gene for a dominant disorder will not be affected or be only mildly affected with the disorder. In some cases, KBG syndrome may also be caused by spontaneous and random (sporadic) genetic changes (mutations) that occur for unknown reasons. These mutations would then be passed on as autosomal dominant traits.

Affected Populations

KBG syndrome is a very rare disorder that affects males and females; however, documented cases have shown a higher percentage of occurrence in males. Fewer than 20 cases have been reported in the medical literature. Characteristic symptoms are usually evident at birth (congenital). The first case of KBG syndrome was described in 1975.

Standard Therapies

KBG syndrome may be detected at birth based on typical physical findings such as skeletal abnormalities and characteristic facial and dental features. Orthopedic surgery may be particularly helpful to correct hip and spine abnormalities of affected individuals. Hearing aids, speech therapy, and comprehensive dental care may also be beneficial.



A supportive team approach for children with KBG syndrome as well as genetic counseling may be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.

Investigational Therapies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.



For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:



Tollfree: (800) 411-1222

TTY: (866) 411-1010

Email: prpl@cc.nih.gov



For information about clinical trials sponsored by private sources, contact:

www.centerwatch.com

References

TEXTBOOKS

Magalini SI, et al., eds. Dictionary of Medical Syndromes. 4th ed.New York, NY: Lippincott-Raven Publishers; 1997:484.



Gorlin RJ, et al., eds. Syndromes of the Head and Neck, 3rd ed. New York, NY: Oxford University Press; 1990:840-1.



Buyce ML, ed. Birth Defects Encyclopedia. Dover, MA: Blackwell Scientific Publications; For: The Center for Birth Defects Information Services Inc; 1990:1000-01.



JOURNAL ARTICLES

Dowling PA, et al. The KBG syndrome, characteristic dental findings: a case report. Int J Paediatr Dent. 2001;11:131-34.



Smithson SF, et al. The KBG syndrome. Clin Dysmorphol. 2000;9:87-91.



Mathieu M, et al. The KBG syndrome: an additional sporadic case. Genet Couns. 2000;11:33-35.



Soekarman D, et al. The KBG syndrome: follow-up data on three affected brothers. Clin Genet. 1994;46:283-86.



Zollarion M, et al. Six additional cases of the KBG syndrome: clinical reports and outline of the diagnostic criteria. Am J Med Genet. 1994;52:302-07.



Fryns JP, et al. Mental retardation, short stature, minor skeletal anomalies, craniofacial dysmorphism and macrodontia in two sisters and their mother. Another variant example of KBG syndrome? Clin Genet. 1984;26:69-72.



Parloir C, et al. Short stature, craniofacial dysmorphism, and dento-skeletal abnormalities in a large kindred. A variant of KBG syndrome or a new mental retardation syndrome. Clin Genet. 1977;12:263-66.



Hermann J, et al. The KBG syndrome - a syndrome of short stature, characteristic facies, mental retardation, macrodontia and skeletal anomalies. Birth Defects. 1975;11:7-18.



FROM THE INTERNET

McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore. MD: The Johns Hopkins University; Entry No: 148050; Last Update:7/10/00.

Resources

Children's Craniofacial Association

13140 Coit Road

Suite 517

Dallas, TX 75240

USA

Tel: (214)570-9099

Fax: (214)570-8811

Tel: (800)535-3643

Email: contactCCA@ccakids.com

Internet: http://www.ccakids.com



FACES: The National Craniofacial Association

PO Box 11082

Chattanooga, TN 37401

Tel: (423)266-1632

Fax: (423)267-3124

Tel: (800)332-2373

Email: faces@faces-cranio.org

Internet: http://www.faces-cranio.org



The Arc

1825 K Street NW, Suite 1200

Washington, DC 20006

Tel: (202)534-3700

Fax: (202)534-3731

Tel: (800)433-5255

TDD: (817)277-0553

Email: info@thearc.org

Internet: http://www.thearc.org



New York State Office for People with Developmental Disabilities

44 Holland Avenue

Albany, NY 12229

Tel: (866)946-9733

TDD: (866)933-4889

Email: Commissioners.Correspondence.Unit@omr.state.ny.us

Internet: http://www.omr.state.ny.us/ws/ws_ibr_resources.jsp



NIH/National Institute of Dental and Craniofacial Research

Building 31, Room 2C39

31 Center Drive, MSC 2290

Bethesda, MD 20892

USA

Tel: (301)496-4261

Fax: (301)480-4098

Tel: (866)232-4528

Email: nidcrinfo@mail.nih.gov

Internet: http://www.nidcr.nih.gov/



NIH/National Institute of Child Health and Human Development

31 Center Dr

Building 31, Room 2A32

MSC2425

Bethesda, MD 20892

Fax: (866)760-5947

Tel: (800)370-2943

TDD: (888)320-6942

Email: NICHDInformationResourceCenter@mail.nih.gov

Internet: http://www.nichd.nih.gov/



Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223

Internet: http://rarediseases.info.nih.gov/GARD/



For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into myCigna.com. For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see http://www.rarediseases.org/search/rdblist.html.

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