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Cat-Eye Syndrome, Marker Chromosome 22

Clinical Features

The characteristic feature of patients with cat eye syndrome is colobomas (in approximately 55-60% of cases). Mental retardation is usually mild; absence of or severe mental retardation are rare.

Features include:

• Developmental delay:

Mild to moderate mental retardation

• Dysmorphic features:

Auricular appendices
Hypertelorism
Low-set, dysplastic ears
Epicanthus medialis
Micrognathia

• Clinical features:

Anal atresia, urogenital abnormalities
Heart defects (approx. 30% of cases; septum defects)
Skeletal abnormalities (missing ribs, synostoses)

Genetic Information

In most affected patients, karyotyping shows an additional dicentric marker chromosome 22 consisting of two short arms of chromosome 22 and parts of the long arm with a breakpoint in band 22q11; mosaics also occur.
Two types of marker chromosome 22 are distinguishable:
• Type I, with breakpoints in the proximal low copy repeat (LCR); the DiGeorge region is not involved.
• Type II, with one or both breakpoints in distal LCR; one or two copies of the DiGeorge critical region are present.
Rare events include interstitial duplications in 22q11 without the presence of a marker chromosome.

Diagnostic