Keratoconus Posticus Circumscriptus
Patient Information
Characteristics
Background and History
This name has been applied to a small number of individuals with a combination of findings that may or may represent a unique condition. The title is descriptive only and refers to a specific deformity of the cornea (windshield of the eye).
Clinical Correlations
The cornea has an indentation on the posterior surface and the overlying area is scarred and opaque. Growth delay is common and many are short in stature with short fingers and limbs. The neck is often short as well and the hairline in back is low. Developmental delays and mental retardation are common. Cleft lip and palate can be present and scoliosis sometimes develops as a result of vertebral anomalies.
Genetics
Inheritance
The etiology of this condition is unknown but the rare familial cases reported suggest autosomal recessive inheritance. No gene mutation has been found.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
The diagnosis is based on a collaborative effort by ophthalmologists, pediatricians and orthopedists. No information on longevity is available but the combination of anomalies requires supportive care for patients. Surgical repair may be beneficial for various bony defects such as scoliosis and clefting abnormalities.
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