Ring chromosome 22

Alternate names

Chromosome 22 ring; Ring 22; R22

Definition

Ring chromosome 22 is a rare condition caused by having an abnormal chromosome 22 that forms a ring.

Epidemiology

Over 100 cases have been reported on ring chromosome 22.

Cause

• In this chromosome abnormality, a segment on the short (p) arm and a segment on the long (q) arm of 22 are missing.
• The amount of material lost varies from person to person.
• The remaining ends of chromosome 22 have joined together to make a ring shape.
• Chromosome 22 is an acrocentric chromosome, meaning that the centromere is near one end, creating a very small short (p) arm that does not contain genes that are relevant to development.
• Thus, only the lost genes on the long (q) arm matter.
• Knowing the breakpoint in the long arm is likely more helpful.

Inheritance

Most cases are sporadic (happen by chance) and occur in people with no history of the condition in their family.

Signs and symptoms

• The associated signs and symptoms depend largely on where the breakpoint occurs on chromosome 22 and how much genetic material has been lost on the long (q) arm.
• Genetic material lost on the short (p) arm is usually irrelevant and does not cause physical or intellectual features.
• The breakpoints on the long (q) arm can be difficult to determine; but in ring chromosome 22, they are most likely to happen somewhere in the terminal segment of the distal band 22q13.
• There is no consistent clinical picture, frequent findings of ring chromosome 22 include developmental delay, moderate to severe learning difficulties or intellectual disabilities, small head, absent or delayed speech, hypotonia, unsteady manner of walking, hyperactivity, autistic behaviors, seizures, and growth delay.
• Some affected individuals may also have relatively mild, non-specific physical features, whereas others may have more distinctive, potentially severe physical abnormalities.

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed

30%-79% of people have these symptoms

• 2-3 toe syndactyly
• Webbed 2nd and 3rd toes
• Autistic behavior
• Azoospermia(Absent sperm in semen)
• Bulbous nose
• Delayed speech and language development(Deficiency of speech development)
• Developmental regression(Loss of developmental milestones)
• Dolichocephaly(Long, narrow head)
• Epicanthus(Eye folds)
• Full cheeks(Apple cheeks)
• Gait ataxia(Inability to coordinate movements when walking)
• Generalized hypotonia(Decreased muscle tone)
• Global developmental delay
• Growth delay(Delayed growth)
• Impaired pain sensation(Decreased pain sensation)
• Inappropriate behavior
• Large hands(large hand)
• Long face(Elongation of face)
• Lymphedema(Swelling caused by excess lymph fluid under skin)
• Macrotia(Large ears)
• Microcephaly(Abnormally small skull)
• Midface retrusion(Decreased size of midface)
• Neurofibromas
• Pointed chin(Pointy chin)
• Protruding tongue(Prominent tongue)
• Seizure
• Thick eyebrow(Bushy eyebrows)
• Thick vermilion border(Full lips)
• Toenail dysplasia(Abnormal toenail development)
• Wide nasal base(Broad base of nose)

5%-29% of people have these symptoms

• Absent septum pellucidum
• Agenesis of corpus callosum
• Pleural effusion(Fluid around lungs)

Diagnosis

Chromosome disorders may be suspected in people who have developmental delays, intellectual disabilities and/or physical abnormalities.

Several types of genetic tests can identify chromosome disorders:

• Karyotyping
• Microarray (also called array CGH)
• Fluorescence in situ hybridization (FISH)

Treatment

• Treatment is symptomatic and supportive.
• Special education is generally indicated due to intellectual disability, while speech therapy may partially overcome speech delays.
• Physical therapy can assist with hypotonia.
• Genetic counselling is broadly indicated for potentially heritable genetic disorders.

NIH genetic and rare disease info

• NIH info on Ring chromosome 22

Ring chromosome 22 is a rare disease.

Ring chromosome 22 Resources
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NIH genetic and rare disease info

• NIH info on Ring chromosome 22

Ring chromosome 22 is a rare disease.

Resources

Frequently asked questions

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