Mutations in KIF14, Encoding Kinesin-Like Protein KIF14, Cause Primary and Syndromic Microcephaly

Primary microcephaly (small head) is a neurodevelopmental disorder characterized by a reduction in the size of the cerebral cortex accompanied with mild to moderate intellectual disability. This condition is observed either as an isolated form referred to as autosomal recessive primary microcephaly (MCPH) or in combination with additional features like growth retardation, renal and cranio-facial abnormalities or others subsumed under syndromic microcephaly. Both MCPH and syndromic microcephaly are heterogeneous disorders caused by mutations of many different genes. The majority of these genes encode proteins implicated in cell division and many of them have been localized at the centrosome.

We studied an MCPH family from Pakistan with three affected individuals and identified a homozygous nonsense mutation in KIF14 (NM_014875.2;c.263T>A;p.L88*) as the likely cause by combining the data of homozygosity mapping and whole-exome sequencing. Further, in a German patient presenting with a severe form of primary microcephaly, we identified compound heterozygous missense mutations in KIF14 (NM_014875.2;c.2545C>G;p.His849Asp and c.3662G>T;p.Gly1221Val). This patient showed a markedly simplified gyral pattern, cerebellar hypoplasia and renal anomalies. Interestingly, the nonsense mutation of the Pakistani family also impaired splicing as it induced skipping of 372bp of exon 2. Aberrant splicing was also detected as a consequence of mutation c.3662G>T in the German patient, resulting in the skipping of the entire exon 24 and thus presumably results in the production of an abnormal protein with a deletion of 76 amino acids (p.Gly1221_Lys1296delinsVal). Similarly, in the Pakistani patients, truncated kinesin-like protein KIF14 is likely to be produced along with some amount of mutant protein lacking 124 amino acids (p.Gly58_Leu181del). This hypothesis was corroborated by immunoblotting of fibroblasts which showed reduced amounts of KIF14 as compared with wild-type cells. Intriguingly, virtually no KIF14 was detected on immunoblots of the German patient’s fibroblasts, documenting a severe impact of both missense mutations on KIF14 expression. Quantification of the amounts of mutant KIF14 transcripts in comparison to wild type also supported this data.

Human kinesin-like protein KIF14, a microtubule motor protein is located at the mitotic spindle (metaphase), spindle midzone (anaphase), and midbody (cytokinesis). It plays diverse roles in efficient cytokinesis, chromosome congression and alignment. We investigated the localization and cellular abnormalities in patient-derived fibroblasts. As expected, immunoreactivity of KIF14 was not seen at the midbody of all patient cells. Interestingly, CRIK (Citron Rho-interacting kinase), which is recruited by KIF14 at the midbody for efficient cytokinesis, was also not detected in the patient cells. No abnormalities of the spindle microtubules and centrosomes were observed. However, significant amounts of micronuclei, misshapen nuclei, apoptotic cells and binucleated cells produced as a consequence of a failure in cytokinesis followed by apoptosis were recorded.

This is the first time that KIF14 mutations have been found in viable individuals. Based on our data, we propose that differences in the amount of residual kinesin-like protein KIF14 correlate with the severity of the phenotype since a moderately reduced level, as observed in the Pakistani patients, resulted in brain-related phenotypes only (MCPH) while the severe reduction seen in the German patient goes along with impaired renal functions in addition to the disturbed brain development.