Kleefstra syndrome

Chromosome 9q deletion syndrome, 9q34.3 deletion syndrome, 9q34.3 microdeletion syndrome, 9q- syndrome


Type of disease: Rare conditions

Kleefstra syndrome, also known as a 9q34.3 deletion, falls into a category of chromosome disorders in which a small segment of chromosome 9 is missing. This means instead of two copies of the genes in this segment, each cell of the body now only has one copy. The missing copy of genetic information may cause multiple birth defects and developmental issues.

Symptoms of this condition may include developmental delays, requiring support with learning, low muscle tone (hypotonia), heart conditions, seizures, high pain tolerance, and an increased risk for developing respiratory infections. Most affected children are not able to use verbal speech, so they generally use nonverbal forms of communication like hand gestures. Individuals with this condition generally have a similar appearance of a broad head, low eyebrows that sometimes meet in the middle, wide spaced eyes, a short upturned nose, large tongue, and a narrow mouth with a pushed out bottom lip.

Mutations (changes) in the gene EHMT1 are what cause Kleefstra syndrome. The condition can be inherited from a parent in an autosomal dominant manner (a mutation in one copy of the gene causes the condition). However, the condition more commonly arises by random chance (de novo), and the parents’ chromosomes are normal. The condition is officially diagnosed with a genetic test that allows a specialist to see that a specific portion of the chromosome is missing.

Although there is currently no cure for Kleefstra syndrome, there are various resources to help manage the condition and treat birth defects. Doctors seek help from various therapists and community services to provide support and care for families. Support groups are also a great resource for support and information. Talk with a genetic counselor or specialist if you or someone in your family has been diagnosed with Kleefstra syndrome.

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