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Features include very common findings: Everted lower lip vermilion, Brachycephaly, Hypertelorism, and Anteverted nares and others; and common findings: Cryptorchidism, Abnormal testis morphology, Macroglossia, and Microcephaly and others. 55 total HPO annotations.
Organ System | Phenotype Count | Example Features |
|---|---|---|
Brain and nerves | 18 | Intellectual disability, Global developmental delay, Specific learning disability |
Phenotype severity distribution: 14 very common features, 15 common features.
Estimated prevalence: <1 in 1,000,000 (VERY_RARE).
No clinical trials have been registered for Kleefstra syndrome due to 9q34 microdeletion.
9 publications have been identified in PubMed for Kleefstra syndrome due to 9q34 microdeletion. Research spans Review / Meta-Analysis (44%), Case Report / Case Series (33%), and Other (11%).
Xie H (2025). [PMID: 40075254](https://pubmed.ncbi.nlm.nih.gov/40075254/). *BMC Cardiovasc Disord*. [Review / Meta-Analysis]
Tzetis M (2025). [PMID: 40428343](https://pubmed.ncbi.nlm.nih.gov/40428343/). *Genes (Basel)*. [Review / Meta-Analysis]
Yang T (2025). [PMID: 41275302](https://pubmed.ncbi.nlm.nih.gov/41275302/). *Orphanet J Rare Dis*. [Epidemiology / Natural History]
Veronese A (2025). [PMID: 39821785](https://pubmed.ncbi.nlm.nih.gov/39821785/). *Neuropediatrics*. [Other]
Giliberti A (2025). [PMID: 40394668](https://pubmed.ncbi.nlm.nih.gov/40394668/). *Ital J Pediatr*. [Case Report / Case Series]
Data assembled from 4 of 12 sources · Last updated Sep 20, 2026, 1:02 AM UTC
European rare disease database
Genetic and Rare Diseases Info Center
Common questions about Kleefstra syndrome due to 9q34 microdeletion
Muscles | 3 | Low muscle tone (hypotonia), Cerebral cortical atrophy, Subcortical cerebral atrophy |
Heart and blood vessels | 3 | Abnormal cardiac septum morphology, Aortic valve stenosis, Aortic regurgitation |
Head and neck | 2 | Everted lower lip vermilion, Microcephaly |
Growth and development | 2 | Failure to thrive, Growth delay |
Kidneys and urinary system | 1 | Reduced kidney function (renal insufficiency) |
Ears | 1 | Hearing loss (hearing impairment) |
Digestive system | 1 | Feeding difficulties |
Bones and joints | 1 | Femoral hernia |
Tai YY (2024). [PMID: 39482011](https://pubmed.ncbi.nlm.nih.gov/39482011/). *Taiwan J Obstet Gynecol*. [Review / Meta-Analysis]
Silva-Carvalho AÉ (2024). [PMID: 38997742](https://pubmed.ncbi.nlm.nih.gov/38997742/). *Cancer Cell Int*. [Review / Meta-Analysis]
Ghaffari S (2024). [PMID: 38988845](https://pubmed.ncbi.nlm.nih.gov/38988845/). *Iran J Child Neurol*. [Case Report / Case Series]