Heart Defects Present in Kleefstra Syndrome (9q34 deletion)

9q34 deletion syndrome, also known as Kleefstra syndrome, is a rare genetic disorder. Terminal deletions of chromosome 9q34 have been associated with childhood hypotonia, a distinctive facial appearance and developmental disability. The facial features typically described include arched eyebrows, small head circumference, midface hypoplasia, prominent jaw and a pouting lower lip. Individuals with this disease may often have speech impediments, such as speech delays. Other characteristics of this disease include: epilepsy, congenital and urogenetic defects, microcephaly, corpulence, and psychiatric disorders.

From analysis of chromosomal breakpoints, as well as gene sequencing in suggestive cases, Kleefstra and colleagues identified EHMT1 as the causative gene. This gene is responsible for producing the protein Histone methyltransferase which functions to alter histones. Ultimately, histone methyltransferases are important in deactivating certain genes, needed for proper growth and development. Moreover, a frameshift, missense, or nonsense error in the coding sequence of EHMT1 can result in this condition in an individual.

Kleefstra syndrome is a new condition that has only been known about for a few years and there have been fewer than 200 cases, reported. Due to the lack of cases worldwide, however, the history behind the origination is unclear. Despite the associated effects of Kleefstra, there is insubstantial information regarding to the lethality of Kleefstra’s. Most the of the documented cases are de novo with the exception of one case due to hereditary factors; however, some cases may be a result of chromosomal translocations.

Signs and symptoms:

Heart Defects
Characteristics of Autism
Genital defects (in males)
Childhood hypotonia
Respiratory infections
Motor Delay
Renal defects
Behavioural Symptoms
Biting, and/or hitting
Disliking routine changes


Tests are either conducted at birth, or later in early childhood via: fluorescence in situ hybridization (FISH), multiplex ligation-dependent probe amplification (MLPA), array comparative genomic hybridization (aCGH), and EHMT1 sequencing.


Unfortunately, there are currently no existing treatments for Kleefstra syndrome.


Kleefstra syndrome affects males and females equally and approximately, 75% of all documented cases are caused by Eu-HMTase1 disruptions while only 25% are caused by 9q34.3 deletions. Additionally, Kleefstra syndrome can also be caused by deletions of the 9q34.3 gene. There are no statistics on the affect the disease has on life expectancy due to the lack of information available.

Source: Wikipedia

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