Myhre Syndrome

Myhre Syndrome

National Organization for Rare Disorders, Inc.

Important

It is possible that the main title of the report Myhre 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

  • Growth-Mental Deficiency Syndrome of Myhre

Disorder Subdivisions

  • None

General Discussion

Myhre syndrome is an extremely rare inherited disorder characterized by mental retardation, short stature, unusual facial features, and various bone (skeletal) abnormalities. Characteristic facial features may include abnormally narrow skin folds (palpebral fissures) between the upper and lower eyelids (blepharophimosis), underdevelopment of the upper jaw bone (maxillary hypoplasia), and an unusually prominent jaw (prognathism). Other findings may include hearing impairment, abnormal enlargement of the muscles (muscular hypertrophy), and/or joint stiffness. Myhre syndrome is thought to be inherited as an autosomal dominant genetic trait.

Symptoms

Myhre syndrome is an extremely rare inherited disorder characterized by mental retardation and growth deficiencies resulting in short stature. Other physical characteristics associated with this disorder may include unusual facial features, various skeletal deformities, and/or abnormal enlargement of the muscles (muscular hypertrophy). Some affected individuals may also have abnormalities of the heart and/or genitals.



Children with Myhre syndrome typically exhibit growth deficiency before birth (prenatally), resulting in low birth weight. During infancy and childhood, growth delays continue resulting in short stature.



In addition, infants with Myhre syndrome usually have several abnormalities of the head and facial (craniofacial) area. Major findings may include upper and lower eyelid folds (palpebral fissures) that are narrower than normal (blepharophimosis), underdevelopment of the upper jaw bone (maxillary hypoplasia), and/or an unusually prominent jaw (prognathism). Affected individuals may also have a shorter than normal groove in the upper lip (philtrum) and/or an unusually small mouth. In some cases, affected children may develop hearing impairment (mixed conductive and sensory types).



Infants with this syndrome may also exhibit several skeletal abnormalities. Certain bones of the skull on the top of the head (calvaria) may be abnormally thick. The ribs may be abnormally broad and wide, and the upper portions of the hip bone may be underdeveloped (hypoplastic iliac wings). The long bones of the body (i.e., those in the arms and legs) may be unusually narrow, round (tubular), and short. In some affected individuals, the bones that surround the spinal cord (vertebrae) may be unusually large.



In early childhood, abnormal enlargement of certain muscles (generalized muscular hypertrophy), especially those of the arms and legs, may become obvious. Some affected infants may also experience stiff joints resulting in limited mobility.



In some cases, affected individuals may exhibit additional symptoms including abnormalities of the heart that are present at birth (congenital heart defects) and/or failure of the testes to descend into the scrotum in males (cryptorchidism).

Causes

The exact cause of Myhre syndrome is unknown. One theory suggests that an underlying metabolic defect may cause the disorder. Because of the advanced age of the fathers of affected individuals, most cases probably occur randomly as the result of a spontaneous genetic change (i.e., new mutation). Inheritance of the mutation is believed to be autosomal dominant.



Genetic diseases are determined by 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.



The gene or genes responsible for Myhre syndrome have not yet been identified. However, the disorder does appear to be transmitted as a dominant trait.



Genetic diseases are determined by the combination of genes for a particular trait which are on the chromosomes receied from the father and the mother.



All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.



The gene or genes responsible for Myhre syndrome have not yet been identified. However, the disorder does appear to be transmitted as a dominant trait.



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.

Affected Populations

Myhre syndrome is an extremely rare inherited disorder that, in theory, affects males and females in equal numbers. Eleven male cases and two females cases have been reported in the medical literature.

Standard Therapies

Diagnosis

A provisional diagnosis of Myhre syndrome is usually confirmed on the basis of a thorough clinical evaluation, identification of characteristic physical findings, a detailed patient history, and/or specialized tests (particularly advanced imaging techniques).



Mental retardation is present at birth, but is usually not detected until the infant is old enough to respond to clinical testing. Clinical evaluation should be conducted early in development and on a continuing basis to help determine the presence and extent of mental retardation. Such evaluation can help ensure that appropriate steps are taken to help affected individuals reach their potential.



Characteristic facial features, skeletal malformations, and/or heart defects may also be present at birth. Specialized X-ray tests may be used to identify skeletal malformations. Advanced imaging techniques (e.g., echocardiogram) may help to determine the exact nature of heart defects.



Growth retardation, abnormally stiff joints, and hearing impairment may not become obvious until late infancy or early childhood. Periodic testing of an infant's or child's hearing is essential to detect any loss in hearing capability. In early childhood, muscle enlargement (generalized muscular hypertrophy) may also be observed.



Treatment

The treatment of Myhre syndrome is directed toward the specific symptoms that are apparent in each individual. Treatment may require the coordinated efforts of a team of specialists. Pediatricians, speech pathologists, specialists who diagnose and treat skeletal disorders (orthopedists), specialists who diagnose and treat disorders of the heart (cardiologists), specialists who assess and treat hearing problems (audiologists), physical therapists and other health care professionals may need to systematically and comprehensively plan an affected child's treatment.



In some cases, other abnormalities (e.g., malformation of the jaw, congenital heart defects, and/or cryptorchidism) may require surgical intervention.



Early intervention is important to ensure that children with Myhre syndrome reach their potential. Special services that may be beneficial to affected children may include special remedial education, special social support, physical therapy, and other medical, social, and/or vocational services.



Genetic counseling will be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.

Investigational Therapies

Research on genetic disorders and their causes is ongoing. The National Institutes of Health (NIH) is sponsoring the Human Genome Project which is aimed at mapping every gene in the human body and learning why they sometimes malfunction. It is hoped that this new knowledge will lead to prevention and treatment of genetic and familial disorders in the future.



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

Whitefors ML. Myhre Syndrome. In: NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:225.



Buyce ML. editor-in-chief. Birth Defects Encyclopedia. Blackwell Scientific Publications. Center for Birth Defects Information Services, Inc., Dover, MA; 1990:817-18.



JOURNAL ARTICLES

Lopez-Cardona MG, Garcia-Cruz D, Garcia-Ortiz JE, et al. Second female case of Myhre syndrome. Clin Dysmorphol. 2004;13:91-4.



Davalos NO, Garcia-Ortiz JE, Garcia-Cruz D, Feria-Velasco A, Sanchez-Corona J. Myhre syndrome: first female case. Clin Dysmorphol. 2003;12:119-21.



Whiteford ML, Doig WB, Raine PA, et al. A new case of Myhre syndrome. Clin Dysmorphol. 2001;10:135-40.



Titomanlio L, Marzano MG, Rossi E, et al. Case of Myhre syndrome with autism and peculiar skin histological findings. Am J Med Genet. 2001;103:163-65.



Figuera LE. Geleophysic dysplasia vs. Myhre syndrome. Am J Med Genet. 1996;65:361-62.



Bottani A, Verloes A. Myhre-Gombo syndrome: possible lumping of two "old" new syndromes. Am J Med Genet. 1995;59:523-24.



FROM THE INTERNET

McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. Growth-Mental Deficiency Syndrome of Myhre. Entry Number; 139210: Last Edit Date; 3/19/04.



McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). The Johns Hopkins University. GOMBO Syndrome. Entry Number; 233270: Last Edit Date; 12/1/2000.

Neuromuscular Center. Washington University of St. Louis. Myhre syndrome. nd. 1p.

www.neuro.wustl.edu/neuromuscular/mother/mlarge.html#myhre



Multiple Congenital Anomaly/Mental Retardation (MCA/MR) Syndromes. Myhre Syndrome. 2pp.

www.nlm.nih.gov/jablonski/syndrome_cgi?term=Myhre+syndrome&field=name



Multiple Congenital Anomaly/Mental Retardation (MCA/MR) Syndromes. Growth retardation-ocular abnormalities-microcephaly-brachydactyly-oligophrenia (GOMBO) syndrome. nd. 1p.

www.nlm.nih.gov/mesh/jablonskisyndromes/syndrome327.htm

Resources

Little People of America, Inc.

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Email: info@lpaonline.org

Internet: http://www.lpaonline.org/



Coalition for Heritable Disorders of Connective Tissue (CHDCT)

4301 Connecticut Avenue, NW Suite 404

Washington, DC 20008

Tel: (202)362-9599

Fax: (202)966-8553

Tel: (800)778-7171

Email: chdct@pxe.org

Internet: http://www.chdct2.org/



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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