Chromosome 1q21.1 duplication syndrome

Alternate names

1q21.1 microduplication syndrome

Definition

1q21.1 microduplication is a chromosomal change in which a small amount of genetic material on chromosome 1 is abnormally copied (duplicated). The duplication occurs on the long (q) arm of the chromosome at a location designated q21.1.

Epidemiology

1q21.1 microduplications occur in about 3 in 10,000 individuals in the general population.

Cause

• The duplication occurs when part of chromosome 1 is copied (duplicated) abnormally, resulting in the extra genetic material from the duplicated segment.
• If the condition is inherited from a parent, it means that one of the parents also has the extra piece of genetic material.
• In these cases, the parent with the duplication has a 50% chance with each pregnancy to pass the duplication on to his/her child.
• The only way to know if it has been inherited from a parent is for the parents to have genetic testing.
• A parent with the duplication may not have any signs or symptoms.
• In both cases, nothing that either parent does, or does not do, can cause this syndrome to occur.

Inheritance

• Chromosome 1q21.1 duplication syndrome can occur sporadically (by chance) from a de novo mutation or can be inherited in an autosomal dominant manner from a parent that has the same duplication.
• When the condition occurs sporadically, it is caused by a random error during the formation of the egg or sperm cell, or during the early days after fertilization.

Signs and symptoms

• Some people with a 1q21.1 microduplication have developmental delay and intellectual disability that is typically mild to moderate.
• Individuals with this condition can also have features of autism spectrum disorder.
• These disorders are characterized by impaired communication and socialization skills, as well as delayed development of speech and language.
• Expressive language skills (vocabulary and the production of speech) tend to be more impaired than receptive language skills (the ability to understand speech) in affected individuals.
• In childhood, 1q21.1 microduplications may also be associated with an increased risk of attention-deficit/hyperactivity disorder (ADHD) and other behavioral problems.
• Psychiatric disorders such as schizophrenia or mood disorders such as anxiety or depression occur in some affected individuals, usually during adulthood.
• Rarely, recurrent seizures (epilepsy) occur in people with a 1q21.1 microduplication.
• Some individuals with a 1q21.1 microduplication are born with malformations of the heart, including a particular combination of heart defects known as tetralogy of Fallot.
• Less commonly, other physical malformations such as the urethra opening on the underside of the penis (hypospadias) in males, inward- and upward-turning feet (clubfeet), or misalignment of the hip joint (hip dysplasia) are present at birth.
• Individuals with a 1q21.1 microduplication may also have a larger than average head size or taller than average adult stature.
• Some have slightly unusual facial features such as wide-set eyes or low-set ears.
• As adults, individuals with a 1q21.1 microduplication may be prone to develop cysts, swollen and knotted (varicose) veins, or carpal tunnel syndrome, which is characterized by numbness, tingling, and weakness in the hands and fingers.
• However, there is no particular pattern of physical abnormalities that characterizes 1q21.1 microduplications.
• Signs and symptoms related to the chromosomal change vary even among affected members of the same family.
• Some people with the duplication have no identified physical, intellectual, or behavioral abnormalities.

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 1q21.1 duplication syndrome

Chromosome 1q21.1 duplication syndrome is a rare disease.

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