9q34

9q34 is a cytogenetic location on the long arm of chromosome 9, designated q34. It refers to a band region used in describing chromosomal abnormalities. Genes located in this region include ABL1 and EHMT1 among others.

The most prominent clinical relevance is the BCR-ABL1 fusion produced by the reciprocal translocation t(9;22)(q34;q11), classically associated with chronic myeloid leukemia and some acute lymphoblastic leukemias. The fusion encodes a constitutively active tyrosine kinase that drives leukemogenesis; targeted tyrosine kinase inhibitors such as imatinib, dasatinib, and nilotinib form standard therapy.

Genetic disorders involving 9q34 also include Kleefstra syndrome, caused by haploinsufficiency of the EHMT1 gene at 9q34.3, and 9q34 microdeletion syndromes that yield variable developmental delay, intellectual disability, dysmorphism, and other features. The precise phenotype depends on the size and gene content of the deletion.

In clinical practice, evaluation of 9q34 abnormalities is performed with karyotyping, fluorescence in situ hybridization (FISH), and array-based methods such as array CGH or SNP arrays, enabling detection of deletions, duplications, or translocations involving this region. Understanding alterations at 9q34 contributes to diagnosis, prognosis, and treatment planning in hematologic malignancies and developmental disorders.