Christianson syndrome explained

Christianson syndrome
Causes:	Mutation in SLC9A6 gene

Christianson syndrome is an X linked syndrome associated with intellectual disability, microcephaly, seizures, ataxia and absent speech.

Presentation

Onset of symptoms is normally within the first year of life with truncal ataxia and seizures. The head is small (microcephaly). Common facial abnormalities include:

Long narrow face
Prominent nose
Prominent jaw
Open mouth

Other common features include:

Uncontrolled drooling
Abnormal eye movements

The associated intellectual disability is usually in the profound range.

Those affected often have a happy demeanor with frequent smiling and spontaneous laughter.

Genetics

This condition is caused by mutations in the SLC9A6 gene. This gene is located on the long arm of the X chromosome (Xq26.3). The gene encodes a sodium/hydrogen exchanger located in the endosomes. Mutations in this gene cause a decrease in the pH (overacidification) of the endosomes.^[1] ^[2]

How this causes the clinical features is not known presently. The inheritance of this condition is X-linked dominant.

Diagnosis

The diagnosis may be suspected on clinical grounds. It is made by sequencing the SLC9A6 gene.

Differential diagnosis

Management

There is presently no curative treatment. Management is supportive.

Epidemiology

The prevalence is not known but this is considered to be a rare disease.

History

This condition was first described in 1999.^[3] The causative mutation was discovered in 2008.^[4]

Notes and References

Pescosolido . Matthew F. . Ouyang . Qing . Liu . Judy S. . Morrow . Eric M. . 2021-11-03 . Loss of Christianson Syndrome Na+/H+ Exchanger 6 (NHE6) Causes Abnormal Endosome Maturation and Trafficking Underlying Lysosome Dysfunction in Neurons . The Journal of Neuroscience . 41 . 44 . 9235–9256 . 10.1523/JNEUROSCI.1244-20.2021 . 1529-2401 . 8570832 . 34526390.
Ouyang . Qing . Lizarraga . Sofia B. . Schmidt . Michael . Yang . Unikora . Gong . Jingyi . Ellisor . Debra . Kauer . Julie A. . Morrow . Eric M. . 2013-10-02 . Christianson syndrome protein NHE6 modulates TrkB endosomal signaling required for neuronal circuit development . Neuron . 80 . 1 . 97–112 . 10.1016/j.neuron.2013.07.043 . 1097-4199 . 3830955 . 24035762.
Christianson AL, Stevenson RE, van der Meyden CH, Pelser J, Theron FW, van Rensburg PL, Chandler M, Schwartz CE (1999) X linked severe mental retardation, craniofacial dysmorphology, epilepsy, ophthalmoplegia, and cerebellar atrophy in a large South African kindred is localised to Xq24-q27. J Med Genet 36:759–766
Gilfillan GD, Selmer KK, Roxrud I, Smith R, Kyllerman M, Eiklid K, Kroken M, Mattingsdal M, Egeland T, Stenmark H, Sjøholm H, Server A, Samuelsson L, Christianson A, Tarpey P, Whibley A, Stratton MR, Futreal PA, Teague J, Edkins S, Gecz J, Turner G, Raymond FL, Schwartz C, Stevenson RE, Undlien DE, Strømme P (2008) SLC9A6 mutations cause X-linked mental retardation, microcephaly, epilepsy, and ataxia, a phenotype mimicking Angelman syndrome. Am J Hum Genet 82:1003–10