OOA (Old Order Amish)

Inheritance: autosomal recessive
Genes: RMRP

CHH
Metaphyseal chondrodysplasia

Dwarfism
Hypopigmentation
Malabsorption
Epiphyseal dysplasia
Metaphyseal dysostosis
Immunodeficiency
Lymphopenia
Sparse hair
Anemia

Cartilage-Hair Hypoplasia

Clinical Characteristics

General description (for patients): 

This disorder was first described by McKusick and coworkers in 1965 as a new form of dwarfism among the Amish. It has since been found in many other populations and is the most common form of short stature among Amish settlements. The hallmarks are short stature and thin, sparse, and light-colored hair. There is considerable variability in these characteristics as well as others such as susceptibility to infections, anemia, skin color, and bowel problems.

Medical description: 

This form of short-limbed dwarfism is caused by a defect in cartilage synthesis with the radiologic appearance of metaphyseal dysostosis.  Cone-shaped epiphyses on X-ray are considered diagnostic.  Loose-jointed digits and limited extension of the elbows may be present together with peculiar Harrison-like groves in the anterolateral chest wall.  Skin pigmentation tends to be light, and hair is thin, sparse and also light-colored, but there is considerable variation in all clinical manifestations.  Anemia, lymphopenia, and leucopenia may be present, and together with a variable immunologic defect leads to an apparent decreased resistance to childhood viral infections, especially varicella and herpes.   A third of affected individuals (32 per cent) have severe or recurrent infections and several (8 per cent) have required bone marrow transplants for combined immunodeficiency.  A defect in T and B cell proliferation has been found, and some reports indicate that there is an increased risk of malignancies such as lymphomas, sarcomas, and liver carcinoma.  A minority of patients have aganglionosis of the bowel and frank Hirschsprung disease with steatorrhea.

Genetics: 

A mutation in a mitochondrial RNA-processing endoribonuclease gene (RMRP) is responsible for this disease. The RNA component of this enzyme is a product of a nuclear gene that then enters a mitochondrion where it is assembled into the ribonucleoprotein. The RMRP gene has been localized to 9p21-p12.  A 70A>G mutation iin this gene seems to be causative among many western populations.  CHH is found among the Old Order Amish in many Amish communities throughout the United States and Canada.  The inheritance pattern is autosomal recessive.

Treatment: 

There is no known treatment for the short stature and sparse hair.  Conventional medical and surgical treatment for aganglionosis and malignancies should be used.  Monitoring with immediate and vigorous treatment of infections is important especially in the first 2 years of life.  Transfusions may be necessary for severe anemia and bone marrow transplantation may be required for infants with severe immunodeficiency.

Prognosis: 

Good medical care and appropriate intervention allows most patients to live normal lives.

Ancillary treatments and support:

Childhood vaccinations for common viral illnesses should be emphasized.  Protection from the sun to reduce the likelihood of skin cancer is recommended.  Appropriate dietary modifications to minimize the impact of steatorrhea are useful.  Because of the risk of malignancy, these patients must be examined periodically throughout life.

Specialists and specialty centers: 

Orthopedist, nutritionist, gastroenterologist, dermatologist.

References:

McKusick, V.A., Eldridge, R., Hostetler, J.A., Ruangwit, U., and Egeland, J.A.: Dwarfism in the Amish. II. Cartilage-hair hypoplasia. Bull. Johns Hopkins Hosp. 116: 285-326, 1965. PubMed ID: 14284412

Makitie, O., Marttinen, E., and Kaitila, I.: Skeletal growth in cartilage-hair hypoplasia – a radiological study of 82 patients. Pediat. Radiol. 22: 434-439, 1992. PubMed ID: 1437368

Sulisalo, T., Francomano, C., A., Sistonien, P., Maher, J.F., McKusick, V. A., de la Chapelle, A., and Kaitila, I.: High-reolution genetic mapping of the cartilage-hair hypoplasia (CHH) gene in Amish and Finnish families. Genomics 20: 347-353, 1994. PubMed ID: 7977356

Rider, N.L., Morton, D.H., Puffenbergere, E., Hendrickson, C.L., Robinson, D.L., and Strauss, K.A.:  Immunologic and clinical features of 25 Amish patients with RMRP 70 A>G cartilage hair hypoplasia.  Clin. Immunol. 131: 119-128, 2009.  PubMed ID:  19150606

Resources:

Little People of America‚Ä®
Immune Deficiency Foundation

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