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McKusick Type Metaphyseal Chondrodysplasia

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Synonyms of McKusick Type Metaphyseal Chondrodysplasia

Disorder Subdivisions

General Discussion

McKusick type metaphyseal chondrodysplasia, also known as cartilage-hair hypoplasia, is a rare progressive inherited disorder characterized by unusually fine, sparse hair and short stature with abnormally short arms and legs (short-limbed dwarfism). Portions of the long bones of the arms and legs develop abnormally with unusual cartilage formations and subsequent abnormal bone formation at the large (bulbous) end portions (metaphyses) of these long bones (metaphyseal chondrodysplasia). In addition, most individuals with McKusick type metaphyseal chondrodysplasia may exhibit impairment of specialized cells (T-cells) that play an important role in helping the body's immune system to fight infection (cellular immunodeficiency). Affected individuals may also have abnormally low levels of certain white blood cells (neutropenia and lymphopenia); low levels of circulating red blood cells (anemia); and/or increased susceptibility to certain infections, such as chickenpox. In some cases, affected infants may also exhibit improper intestinal absorption of certain necessary nutrients (malabsorption) and/or dental abnormalities such as unusually small teeth (microdontia). Some individuals with the disorder may also have additional physical abnormalities. The range and severity of symptoms vary widely from case to case. McKusick type metaphyseal chondrodysplasia is inherited as an autosomal recessive trait.

Symptoms

McKusick type metaphyseal chondrodysplasia is a rare progressive inherited disorder characterized by unusually fine, sparse hair; short stature with abnormally short arms and legs (short-limbed dwarfism); a variety of additional skeletal malformations; and/or abnormalities of the immune and digestive systems. The range and severity of symptoms associated with the disorder vary widely from case to case.

Many affected infants have abnormally fine, sparse, light-colored hair that, in some cases, may also be brittle. In addition, some affected individuals may have very little scalp hair. The eyebrows, eyelashes, and body hair may also be affected. In rare cases, individuals with the disorder may not exhibit such hair abnormalities.

Individuals with McKusick type metaphyseal chondrodysplasia may exhibit growth deficiency before birth (prenatally). In addition, portions of the long bones of the arms and legs develop abnormally with unusual cartilage formations and subsequent abnormal bone formation at the large (bulbous) end portions (metaphyses) of these long bones (metaphyseal chondrodysplasia). As a result, affected individuals exhibit unusually short arms and legs and short stature (short-limbed dwarfism), findings that typically become apparent during childhood.

Abnormal cartilage and bone formation may also affect other bones of the body, including those of the hands and feet (e.g., metacarpals and metatarsals). As affected individuals age, abnormal cartilage formations in the affected areas may harden into round (bulbous) masses of bone, which may become prominent.

Affected infants may also have small wide hands with abnormally short fingers (brachydactyly), unusually short fingernails and toenails, and/or slightly bowed legs (genu varum). In some cases, the calf bone (fibula) may be disproportionately longer than the shin bone (tibia). In addition, affected children may also exhibit unusually flexible (hyperextensible) joints of the hands, wrists, and/or feet. However, some affected children may be unable to completely extend their elbows.

Additional skeletal abnormalities associated with McKusick type metaphyseal chondrodysplasia may include an abnormal horizontal depression across the lower part of the chest (Harrison's groove), an unusually prominent breastbone (sternum), flaring of bones of the lower rib cage, and/or abnormal backward (lordosis) and/or side-to-side (scoliosis) curvature of the spine.

In some cases, infants with McKusick type metaphyseal chondrodysplasia may have abnormalities of the head and facial (craniofacial) area. For example, they may have an unusually short, broad head (brachycephaly) and/or dental abnormalities such as unusually small teeth (microdontia).

In many cases, individuals with McKusick type metaphyseal chondrodysplasia may exhibit impairment of certain cells of the immune system (T-cells) that play an important role in helping the body to fight certain infections (cellular immunodeficiency). In addition, individuals with cellular immunodeficiency may have abnormally low levels of certain white blood cells (i.e., neutropenia and lymphopenia). As a result, affected children may have an increased susceptibility to certain infections, particularly chickenpox (varicella). In addition, they may be unable to fight off such infections due to the improper functioning of their immune systems. Affected children may exhibit diminished immune response against foreign substances (diminished hypersensitivity). In addition, in some cases, children with McKusick type metaphyseal chondrodysplasia may also exhibit abnormally low levels of circulating red blood cells (anemia). The degree of anemia may correspond to the severity of immunodeficiency. In individuals with McKusick type metaphyseal chondrodysplasia, the severity of immunodeficiency varies widely from case to case.

Infants with McKusick type metaphyseal chondrodysplasia may also have abnormalities of the digestive system. For example, they may exhibit improper intestinal absorption of certain necessary nutrients (intestinal malabsorption). In addition, in some cases, affected infants may have Hirschsprung's disease, a disorder in which absence of nerve fibers (ganglia) in the muscle wall of the colon prevents the muscles from efficiently pushing waste materials (feces) through the lower digestive tract. As a result, feces abnormally accumulate within the colon. (For more information on Hirschsprung's disease, please see the Related Disorders section of this report below.)

In rare cases, some individuals with McKusick type metaphyseal chondrodysplasia appear more prone to developing certain malignancies (e.g., Hodgkin's disease, lymphoma, or leukemia) than the general population. (For information on these disorders, choose the specific disorder name as your search term in the Rare Disease Database.)

Causes

McKusick type metaphyseal chondrodysplasia is inherited as an autosomal recessive trait. Genetic diseases are determined by two genes, one received from the father and one from the mother.

Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%.

Investigators have determined that McKusick type metaphyseal chondrodysplasia may be caused by disruption or changes (mutations) of the mitochondrial RNA-processing endoribonuclease (RMRP) gene located on the short arm (p) of chromosome 9 (9p21-p12). Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males, and two X chromosomes for females. Each chromosome has a short arm designated as "p" and a long arm identified by the letter "q." Chromosomes are further subdivided into bands that are numbered.

Some cases of McKusick type metaphyseal chondrodysplasia have had parents who were related by blood (consanguineous). 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 symptoms and findings associated with McKusick type metaphyseal chondrodysplasia (e.g., short stature or the severity of immunodeficiency) may vary greatly from case to case (variable expressivity). In addition, all of the characteristics associated with the disorder may not be manifested in all those who inherit the gene (incomplete penetrance).

According to recent research, T cell deficiency of individuals with McKusick type metaphyseal chondrodysplasia may be due, in part, to increased cell fragmentation and death (apoptosis). More research is needed to determine whether abnormally increased apoptosis is characteristic of a majority of individuals with McKusick type metaphyseal chondrodysplasia.

Affected Populations

McKusick type metaphyseal chondrodysplasia is a rare disorder that affects males and females in equal numbers. Approximately 200 cases have been reported in the medical literature. The disorder was first detected in the Old Order Amish population of the United States and Canada. However, it has been seen all over the world, with a higher occurrence in Finnish populations. According to one estimate, the prevalence of McKusick type metaphyseal chondrodysplasia in the Finnish population is 1 in 23,000 births.

Related Disorders

Symptoms of the following disorders may be similar to those of McKusick type metaphyseal chondrodysplasia. Comparisons may be useful for a differential diagnosis:

Shwachman syndrome is an extremely rare inherited disorder with multiple and varied manifestations. In most cases, the disorder may be characterized by signs of insufficient intestinal absorption (malabsorption) of fats and other nutrients due to abnormal development of the pancreas (pancreatic insufficiency); abnormal bone development affecting the rib cage and/or bones in the arms and/or legs (metaphyseal dysostosis); short stature; and/or improper functioning of the bone marrow (bone marrow dysfunction), resulting in low levels of circulating blood cells (hematologic abnormalities). Due to improper bone changes, individuals with Shwachman syndrome may exhibit abnormal thickening of the ribs and their supporting connective tissue (costochondral thickening), resulting in abnormally short, flared ribs. Children with Shwachman syndrome may also be smaller than expected for their ages, with below average height (short stature) and weight. In addition, as a result of bone marrow dysfunction, individuals with Shwachman syndrome may exhibit a decrease in any or all types of blood cells (e.g., white blood cells [neutropenia], red blood cells [anemia], or all types of blood cells [pancytopenia]). Shwachman syndrome is thought to be inherited as an autosomal recessive trait. (For more information on this disorder, choose "Shwachman" as your search term in the Rare Disease Database.)

Hypochondroplasia is a rare inherited skeletal disorder characterized by short stature with abnormally short arms and legs (short-limbed dwarfism). Major symptoms may include bowing of the legs, abnormally short fingers and toes (brachydactyly), mild limitation of elbow motions, and/or abnormal backward curvature (lordosis) of the spine. In addition, affected children may have abnormalities of the head and face (craniofacial) area including drooping of the upper eyelids (ptosis), an abnormally prominent forehead (frontal bossing), and/or an unusually large head (macrocephaly). Hypochondroplasia is thought to be inherited as an autosomal dominant trait. (For more information on this disorder, choose "Hypochondroplasia" as your search term in the Rare Disease Database.)

Schmid type metaphyseal chondrodysplasia is a very rare inherited disorder characterized by short stature with abnormally short arms and legs (short-limbed dwarfism). Other physical abnormalities associated with this disorder may include flaring of the bones of the lower rib cage, bowed legs (genu varum), pain in the legs, and/or a hip deformity in which the thigh bone angles towards the center of the body (coxa vara). Due to abnormalities of the legs and hips, affected children may walk with an abnormal waddling gait. Schmid type metaphyseal chondrodysplasia is thought to be inherited as an autosomal dominant trait. (For more information on this disorder, choose "Schmid Type Metaphyseal Chondrodysplasia" as your search term in the Rare Disease Database.)

Jansen type metaphyseal chondrodysplasia, an extremely rare inherited disorder, is characterized by severe short stature with abnormally short arms and legs (short-limbed dwarfism) due to improper formation of the cartilage at the end portions (metaphyses) of the long bones (metaphyseal chondrodysplasia). Improper cartilage development may also occur in the metaphyses of other bones of the body, particularly those of the hands and feet (i.e., metacarpals and metatarsals). Affected children may also exhibit malformation of certain bones of the skull; progressive swelling, pain, and stiffness of certain joints; unusually short fingers (brachydactyly); and/or abnormal front-to-back and side-to-side curvature of the spine (kyphoscoliosis). In addition, affected children may have abnormally high levels of calcium in the blood (hypercalcemia). Jansen type metaphyseal chondrodysplasia is thought to be inherited as an autosomal dominant genetic trait. (For more information on this disorder, choose "Jansen Type Metaphyseal Chondrodysplasia" as your search term in the Rare Disease Database.)

Spahr type metaphyseal chondrodysplasia, an extremely rare inherited disorder, is characterized by severely bowed legs and short stature (short-limbed dwarfism) due to abnormal cartilage development of the long bones of the arms and legs (metaphyseal chondrodysplasia). This disorder is very similar to Schmid type metaphyseal chondrodysplasia; however, Spahr type metaphyseal chondrodysplasia is thought to be inherited as an autosomal recessive trait.

The following disorder may be associated with McKusick type metaphyseal chondrodysplasia as a secondary characteristic. It is not necessary for a differential diagnosis:

Hirschsprung's disease, also known as congenital megacolon, is a disorder in which absence of nerve fibers (ganglia) in the muscle wall of the colon prevents the muscles from efficiently pushing waste materials (feces) through the lower digestive tract (peristalsis). As a result, feces accumulate abnormally in the involved portion of the colon, causing massive widening (dilatation) of the colon (megacolon), diarrhea, constipation, abdominal bloating (distention), nausea, episodes of vomiting, and/or loss of appetite (anorexia). (For more information on this disorder, choose "Hirschsprung" as your search term in the Rare Disease Database.)

Standard Therapies

Diagnosis
In most cases, the diagnosis of McKusick type metaphyseal chondrodysplasia may be made by the second or third year of life. Diagnosis of the disorder may be confirmed by a thorough clinical evaluation, identification of characteristic physical findings, a detailed patient history, and a variety of specialized tests, particularly advanced imaging techniques. These include x-ray studies that may reveal malformation and/or characteristic appearance (e.g., scalloped or cupped) of the end portion of the shafts of the long bones (metaphyses).

Children who are diagnosed with McKusick type metaphyseal chondrodysplasia should receive a complete immunological evaluation to determine whether cellular immunodeficiency, particularly improper T-cell function, may be present. In some cases, blood tests may be conducted to detect low levels of red and/or white blood cells as well as diminished effectiveness of white blood cells. For example, certain white blood cells (lymphocytes) normally respond to phytohemagglutinin (PHA) in laboratory (in vitro) tests. Failed or diminished responsiveness of lymphocytes to PHA may further suggest McKusick type metaphyseal chondrodysplasia Phytohemagglutinin is an antibody formed from a protein substance (lectin) found in certain plants.

Treatment
The treatment of McKusick type metaphyseal chondrodysplasia is directed toward the specific symptoms that are apparent in each individual. Treatment may require the coordinated efforts of a team of specialists. Pediatricians, physicians who specialize in treating skeletal disorders (orthopedists), physicians who diagnose and treat skin disorders (dermatologists), physicians who specialize in blood disorders (hematologists), dental specialists, speech pathologists, dietitians, physical therapists, and/or other health care professionals may need to systematically and comprehensively plan an affected child's treatment.

Orthopedic techniques, orthopedic surgery, physical therapy, and/or other supportive techniques may help treat certain skeletal abnormalities potentially associated with McKusick type metaphyseal chondrodysplasia, such as limited range of motion of the elbows and legs.

In addition, physicians may regularly monitor affected individuals for hematological abnormalities (i.e., neutropenia, anemia, lymphopenia) potentially associated with McKusick type metaphyseal chondrodysplasia. In some severe cases of neutropenia, anemia, and/or lymphopenia, transfusions of specific blood components (e.g., neutrophils) may be given to help reduce associated symptoms.

Because individuals with McKusick type metaphyseal chondrodysplasia may have an increased susceptibility to certain infections, physicians may closely monitor affected individuals, recommend preventive measures, and immediately institute appropriate treatment should such infections occur. In severe cases of such infections, hospitalization may be required. In addition, physicians may recommend that small pox and live polio vaccinations be avoided.

Some individuals with this disorder may be more prone to developing certain malignancies than the general population. Although this association is uncommon, physicians may closely monitor an affected individual to ensure early detection and appropriate treatment.

Individuals with Hirschsprung's disease may require surgery during early childhood to remove the damaged (i.e., widened [dilated]) portion of the colon and re-connect the undamaged portions of the large intestine (i.e., colon and rectum). In some cases, before this procedure is performed, a temporary opening for the colon may be made in the abdominal wall (colostomy) to allow passage of feces from the body.

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

Investigational Therapies

In individuals with McKusick type metaphyseal chondrodysplasia who experience severe infection (e.g., a severe case of chickenpox), treatment may include the administration of antiviral agents such as leukocyte interferon or acyclovir.

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

Organizations related to McKusick Type Metaphyseal Chondrodysplasia

(Please note that some of these organizations may provide information concerning certain conditions potentially associated with this disorder [e.g., short stature, immune dysfunction, blood abnormalities, etc.].)

References

TEXTBOOKS
Jones KL, ed. Smith's Recognizable Patterns of Human Malformation. 5th ed. Philadelphia, PA: W. B. Saunders Co: 1997:352, 382-7.

Behrman RE, ed. Nelson Textbook of Pediatrics, 15th ed. Philadelphia, PA: W.B. Saunders Company; 1996:573-4.

Beighton P, ed. Mckusick's Heritable Disorders of Connective Tissue. 5th ed. St. Louis, MO: Mosby-Year Book, Inc; 1993:631-3.

Champion RH, et al., eds. Textbook of Dermatology. 5th ed. Cambridge, MA: Blackwell Scientific Publications; 1992:368.

Buyce ML, ed. Birth Defects Encyclopedia. Dover, MA: Blackwell Scientific Publications; For: The Center for Birth Defects Information Services Inc; 1990:1132-3.

Gorlin RJ, et al., eds. Syndromes of the Head and Neck, 3rd ed. New York, NY: Oxford University Press; 1990:184-7.

JOURNAL ARTICLES
Ridanpaa M, et al. The major mutation in the RMRP gene causing CHH among the Amish is the same as that found in most Finnish cases. Am J Med Genet. 2003;121C:81-3.

Makitie O, et al. Hirschsprung's disease in cartilage-hair hypoplasia has poor prognosis. J Pediatr Surg. 2002;37:1585-8.

Ridanpaa M, et al. Worldwide mutation spectrum in cartilage-hair hypoplasia: ancient founder origin of the major 70A-->G mutation of the untranslated RMRP. Eur J Hum Genet. 2002;10:439-47.

Yel L, et al. Cartilage-hair hypoplasia syndrome: increased apoptosis of T lymphocytes is associated with altered expression of Fas (CD95), FasL (CD95L), IAP, Bax, and Bcl2. J Clin Immunol. 1999 Nov;19:428-34.

Glass RB, et al. Radiologic changes in infancy in McKusick cartilage hair hypoplasia. Am J Med Genet. 1999;86:312-5.

Makitie O, et al. Increased incidence of cancer in patients with cartilage-hair hypoplasia. J Pediatr. 1999;134:315-8.

Sulisalo T, et al. Genetic homogeneity of cartilage-hair hypoplasia. Hum Genet. 1995;95:157-60.

Sulisalo T, et al. Early prenatal diagnosis of cartilage-hair hypoplasia (CHH) with polymorphic DNA markers. Prenat Diagn. 1995;15:135-40.

Sulisado T, et al. High-resolution genetic mapping of the cartilage-hair hypoplasia (CHH) gene in Amish and Finnish families. Genomics. 1994;20:347-53.

Sulisado T, et al. Cartilage-hair hypoplasia gene assigned to chromosome 9 by linkage analysis. Nat Genet. 1993;3:338-41.

Sole D, et al. Cartilage-hair hypoplasia syndrome: immunological evaluation of two cases. Rev Paul Med. 1993;111:314-9.

Makitie O, et al. Cartilage-hair hypoplasia - clinical manifestations in 108 Finnish patients. Eur J Pediatr. 1993;152:211-7.

Makitie O, et al. Skeletal growth in cartilage-hair hypoplasia. A radiological study of 82 patients. Pediatr Radiol. 1992;22:434-39.

Makitie O, et al. Growth in cartilage-hair hypoplasia. Pediatr Res. 1992;31:176-80.

Makitie O, et al. Cartilage-hair hypoplasia in Finland: epidemiological and genetic aspects of 107 patients. J Med Genet. 1992;29:652-5.

van der Burgt I, et al. Cartilage hair hypoplasia, metaphyseal chondrodysplasia type McKusick: descriptioni of seven patients and review of the literature. Am J Med Genet 1991;41:371-80.

Le Merrer M, et al. Cartilage hair hypoplasia in infancy: a misleading chondrodysplasia. Eur J Pediatr. 1991;150:847-51.

Brennan TE, et al. Abnormal elastic tissue in cartilage-hair hypoplasia. Arch Dermatol. 1988;124:1411-4.

Trojak JE, et al. Immunologic studies of cartilage-hair hypoplasia in the Amish. Johns Hopkins Med J. 1981;148:157-64.

FROM THE INTERNET
McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore. MD: The Johns Hopkins University; Entry No:250250; Last Update:9/29/95. Entry Number:156400; Last Edit Date:7/20/95. Entry Number:250400; Last Edit Date 2/19/94.

Report last updated: 2008/05/15 00:00:00 GMT+0