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FB2026_01
,
released March 12, 2026
This report describes microcephaly 17, primary, autosomal recessive (MCPH17), which is a subtype of primary microcephaly. The human gene implicated in this disease is citron rho-interacting serine/threonine kinase (CIT) which plays an important role in the regulation of cytokinesis and the development of the central nervous system. There is a single orthologous gene in Drosophila, Dmel\sti, for which classical loss-of-function alleles, RNAi-targeting constructs and alleles caused by insertional mutagenesis have been generated.
The human CIT gene has not been introduced into flies.
Animals that are homozygous for loss-of-function alleles of Dmel\sti typically die in the larval or early pupal stage. Assessed in third instar larvae, the brains of homozygous animals have high proportions of polyploid cells. It has been shown that Dmel\sti is also involved in repair of DNA double-strand breaks; this role in maintenance of genome integrity appears to be independent of its function in cytokinesis completion. Multiple physical and genetic interactions have been described for Dmel\sti; see below and in the sti gene report.
[updated Feb. 2020 by FlyBase; FBrf0222196]
Primary microcephaly (MCPH) refers to the clinical finding of a head circumference less than 3 standard deviations below the age- and sex-related mean, present at birth. Primary microcephaly is a static developmental anomaly, distinguished from secondary microcephaly, which refers to a progressive neurodegenerative condition. Microcephaly is a disorder of fetal brain growth; individuals with microcephaly have small brains and almost always have mental retardation; additional clinical features may include short stature or mild seizures (review by Woods et al., 2005; pubmed:15806441). [from MIM:251200; 2016.06.16]
[MICROCEPHALY 17, PRIMARY, AUTOSOMAL RECESSIVE; MCPH17](https://omim.org/entry/617090)
[CITRON RHO-INTERACTING SERINE/THREONINE KINASE; CIT](https://omim.org/entry/605629)
Autosomal recessive primary microcephaly-17 (MCPH17) is a severe neurologic disorder characterized by very small head circumference that is apparent at birth and worsens over time (up to -12 SD). Affected individuals have delayed psychomotor development, intellectual disability, spasticity, axial hypotonia, and dysmorphic features. Brain imaging shows a simplified gyral pattern; more severe cases have lissencephaly with hypoplasia of the brainstem and cerebellum (summary by Harding et al., 2016; pubmed:27453579). [from MIM:617090; 2020.02.18]
Autosomal recessive primary microcephaly-17 (MCPH17) is caused by homozygous or compound heterozygous mutation in the CIT gene. [from MIM:617090; 2020.02.18]
Together with the kinesin KIF14, the CIT protein localizes to the central spindle and midbody, and functions to promote efficient cytokinesis. The CIT protein is involved in central nervous system development. [Gene Cards, CIT; 2020.02.18]
One to one: 1 human to 1 Drosophila.
Moderate- to high-scoring ortholog of human CIT (1 Drosophia to 1 human). Dmel\sti shares 27% identity and 46% similarity with the human gene.