Microcornea, Myopia, Telecanthus and Posteriorly-Rotated Ears
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Small corneas measuring 9.8 – 10.5 mm are characteristic. Acuity is usually 20/60 or better in older children but even younger children maintain steady fixation. Refractive errors of -6 to -12.75 diopters are usually present but may be much less in other children. Axial lengths range from 22.42 to 26.84 mm corresponding to the amount of myopia. The degree of myopic chorioretinal change correlates roughly with the amount of axial myopia. Telecanthus is present in all individuals.
Systemic Features
The ears are rotated posteriorly.
Genetics
Inheritance
Five males with this syndrome occurred in four consanquineous/endogamous Saudi families suggesting autosomal recessive inheritance. Homozygous mutations in ADAMTS18 (16q23.1) have been found in these four families. However, one child had a similarly affected father suggesting to some that this may be a pseudodominant disorder.
Mutations in the same gene are responsible for Knobloch syndrome 2 (KNO2) (608454).
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.