Cartilage hair hypoplasia syndrome definition - medical term
A specific genetic form of short-limbed
dwarfism with skeletal features that also include normal head, inability to fully
extends the elbows, chest cage deformity, bow legs (genu varum), and the tibia shorter
than the fibula. The fingers are usually loose-jointed and the fingernails foreshortened.
Biopsy shows hypoplasia (underdevelopment) of cartilage to be the nature of the
skeletal abnormality. The hair is unusually fine, sparse and light-colored. Microscopically,
it has an abnormally small caliber. Many patients with cartilage hair hypoplasia
have a major immunologic defect that is manifested, for example, as an unusual susceptibility
to chickenpox. In addition to lymphopenia (lack of lymphocytes), some patients have
anemia and neutropenia (lack of neutrophiliuc white blood cells). There is an increased
malignancy risk, especially lymphoma and skin cancer. A condition called aganglionic
megacolon (Hirschsprung disease) is also found in some patients.
C artilage hair hypoplasia was first recognized by McKusick and colleagues in
1965 as a distinct entity in the Old Order Amish, a religious isolate, but was later
identified in other groups. In the original study of the Amish, 6 cases of fatal
varicella (chickenpox) pneumonia were noted.
Inheritance of the syndrome is autosomal recessive. The gene is on chromosome
9 in band 9p13. The child who receives the gene from both parents has the syndrome.
Not everyone with the syndrome is dwarfed. Patients may be relatively tall; at least
1 Amish woman with the syndrome is 55 inches tall. There is a remarkable degree
of variability in all features of the syndrome. The hair may be seemingly completely
unaffected; some patients suffer no apparent immunologic or hematologic defect.
Diagnosis of the syndrome in the first year or so of life may be difficult.
Cartilage hair hypoplasia is sometimes written with a hyphen as cartilage-hair
hypoplasia syndrome, is abbreviated CHH, and is also known as metaphyseal chondrodysplasia
of the McKusick type. Perhaps the best known person with the syndrome was Billy
Barty (1924-2000), the diminutive actor, who founded Little People of America, an
important advocacy group for persons with all forms of dwarfism.
Common Misspellings: cartilage hair hypoplasia syndrone
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