Chromosome 3q29 microduplication syndrome

Alternate names

Trisomy 3q29; Microduplication 3q29 syndrome

Definition

Chromosome 3q29 microduplication syndrome is a rare chromosome abnormality characterized by having an extra copy of material (duplication) on a specific part of the long arm of chromosome 3.

Epidemiology

This condition is very rare. Fewer than 30 cases have been described in the medical literature.

Cause

• Most people with 3q29 microduplication syndrome have an extra copy of about 1.6 million DNA building blocks (base pairs), also written as 1.6 megabases (Mb), at position q29 on chromosome 3.
• However, the duplication can vary in size.
• It affects one of the two copies of chromosome 3 in each cell.
• The chromosome segment most commonly duplicated in people with 3q29 microduplication syndrome contains about 20 genes.
• Some of these genes are thought to be involved in brain and eye development.

Inheritance

• The condition may occur for the first time in the affected individual (de novo) or it can be inherited from a mildly affected or apparently normal parent.
• This condition has an autosomal dominant pattern of inheritance, which means the duplication occurs on one copy of chromosome 3 in each cell.

Signs and symptoms

• The signs and symptoms of chromosome 3q29 microduplication syndrome appear to vary among affected individuals.
• This condition has reduced penetrance, which means that some individuals with this chromosome abnormality do not have any signs and symptoms and are clinically unaffected.
• Developmental delay, abnormally small head size (microcephaly) and ophthalmologic (eye-related) findings seem to be the most common features.
• Other signs and symptoms that have been reported in affected individuals include cardiac (heart) abnormalities; poor muscle tone (hypotonia); speech delay; craniosynostosis; high palate (roof of the mouth); dental abnormalities; conductive hearing loss (hearing loss due to mechanical problems in the outer or middle ear); musculoskeletal abnormalities; and seizures.

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

• Abnormality of the dentition(Abnormal dentition)
• Downslanted palpebral fissures(Downward slanting of the opening between the eyelids)
• Global developmental delay
• Intellectual disability(Mental deficiency)
• Microcephaly(Abnormally small skull)
• Muscular hypotonia(Low or weak muscle tone)
• Obesity(Having too much body fat)

5%-29% of people have these symptoms

• Aniridia(Absent iris)
• Biparietal narrowing
• Camptodactyly of toe
• Cataract(Clouding of the lens of the eye)
• Cleft palate(Cleft roof of mouth)
• Craniosynostosis
• Deep philtrum
• Ectopic anus(Abnormal anus position)
• Hearing impairment(Deafness)
• High forehead
• High palate(Elevated palate)
• Iris coloboma(Cat eye)
• Large fontanelles(Wide fontanelles)
• Low-set ears(Low set ears)
• Macrocephaly(Large head circumference)
• Microphthalmia(Abnormally small eyeball)
• Sandal gap(Gap between 1st and 2nd toes)
• Sclerocornea(Hardening of skin and connective tissue)
• Seizure
• Short neck(Decreased length of neck)
• Toe syndactyly(Fused toes)
• Ventricular septal defect(Hole in heart wall separating two lower heart chambers)
• Wide nasal bridge(Broad nasal bridge)

1%-4% of people have these symptoms

• Blepharophimosis(Narrow opening between the eyelids)
• Bulbous nose
• Long face(Elongation of face)
• Low posterior hairline(Low hairline at back of neck)
• Multiple palmar creases(Multiple palm lines)
• Pes planus(Flat feet)
• Round face(Circular face)
• Short nose(Decreased length of nose)

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:

• Karyotype - a karyotype is a laboratory test that produces an image of a person's chromosomes. This test can be used to diagnose large deletions.
• FISH - a laboratory technique that is used to detect and locate a specific DNA sequence on a chromosome. During FISH, a chromosome is exposed to a small DNA sequence called a probe that has a fluorescent molecule attached to it. The probe sequence binds to its corresponding sequence on the chromosome. This test can be used in combination with karyotyping for deletions that are too small to be seen on karyotype, alone. However, FISH is only useful if the person ordering the test suspects there is a deletion of a specific region of 4q.
• Array CGH - a technology that detects deletions that are too small to be seen on karyotype.

Treatment

Treatment is directed toward the specific signs and symptoms present in each individual.

Prognosis

• The prognosis for chromosome 3q29 microduplication syndrome varies depending on the presence and severity of signs and symptoms in each affected individual.
• Because microduplications have only more recently been diagnosed due to improving technology, it is not known with certainty what the long term affects are.
• Those who have no birth defects and are generally healthy likely will have a normal life expectancy, while individuals who are more severely affected may experience various complications.

NIH genetic and rare disease info

• NIH info on Chromosome 3q29 microduplication syndrome

Chromosome 3q29 microduplication syndrome is a rare disease.

Chromosome 3q29 microduplication syndrome Resources
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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: Karyotype - a karyotype is a laboratory test that produces an image of a person's chromosomes. This test can be used to diagnose large deletions. FISH - a laboratory technique that is used to detect and locate a specific DNA sequence on a chromosome. During FISH, a chromosome is exposed to a small DNA sequence called a probe that has a fluorescent molecule attached to it. The probe sequence binds to its corresponding sequence on the chromosome. This test can be used in combination with karyotyping for deletions that are too small to be seen on karyotype, alone. However, FISH is only useful if the person ordering the test suspects there is a deletion of a specific region of 4q. Array CGH - a technology that detects deletions that are too small to be seen on karyotype.

Treatment Treatment is based on the signs and symptoms present in each person.

NIH genetic and rare disease info

• NIH info on Chromosome 3q29 microduplication syndrome

Chromosome 3q29 microduplication syndrome is a rare disease.

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