Congenital microcephaly, juvenile retinal dystrophy and normal mentation in a mildly dysmorphic child

Mutations in TUBGCP4 alter microtubule organization via the γ-tubulin ring complex in autosomal-recessive microcephaly with chorioretinopathy

We have identified TUBGCP4 variants in individuals with autosomal-recessive microcephaly and chorioretinopathy. Whole-exome sequencing performed on one family with two affected siblings and independently on another family with one affected child revealed compound-heterozygous mutations in TUBGCP4. Subsequent Sanger sequencing was performed on a panel of individuals from 12 French families affected by microcephaly and ophthalmic manifestations, and one other individual was identified with compound-heterozygous mutations in TUBGCP4. One synonymous variant was common to all three families and was shown to induce exon skipping; the other mutations were frameshift mutations and a deletion. TUBGCP4 encodes γ-tubulin complex protein 4, a component belonging to the γ-tubulin ring complex (γ-TuRC) and known to regulate the nucleation and organization of microtubules. Functional analysis of individual fibroblasts disclosed reduced levels of the γ-TuRC, altered nucleation and organization of microtubules, abnormal nuclear shape, and aneuploidy. Moreover, zebrafish treated with morpholinos against tubgcp4 were found to have reduced head volume and eye developmental anomalies with chorioretinal dysplasia. In summary, the identification of TUBGCP4 mutations in individuals with microcephaly and a spectrum of anomalies in eye development, particularly photoreceptor anomalies, provides evidence of an important role for the γ-TuRC in brain and eye development.

CDK19 is disrupted in a female patient with bilateral congenital retinal folds, microcephaly and mild mental retardation

Microcephaly, mental retardation and congenital retinal folds along with other systemic features have previously been reported as a separate clinical entity. The sporadic nature of the syndrome and lack of clear inheritance patterns pointed to a genetic heterogeneity. Here, we report a genetic analysis of a female patient with microcephaly, congenital bilateral falciform retinal folds, nystagmus, and mental retardation. Karyotyping revealed a de novo pericentric inversion in chromosome 6 with breakpoints in 6p12.1 and 6q21. Fluorescence in situ hybridization analysis narrowed down the region around the breakpoints, and the breakpoint at 6q21 was found to disrupt the CDK19 gene. CDK19 was found to be expressed in a diverse range of tissues including fetal eye and fetal brain. Quantitative PCR of the CDK19 transcript from Epstein–Barr virus-transformed lymphoblastoid cell lines of the patient revealed ~50% reduction in the transcript (p = 0.02), suggesting haploinsufficiency of the gene. cdk8, the closest orthologue of human CDK19 in Drosophila has been shown to play a major role in eye development. Conditional knock-down of Drosophila cdk8 in multiple dendrite (md) neurons resulted in 35% reduced dendritic branching and altered morphology of the dendritic arbour, which appeared to be due in part to a loss of small higher order branches. In addition, Cdk8 mutant md neurons showed diminished dendritic fields revealing an important role of the CDK19 orthologue in the developing nervous system of Drosophila. This is the first time the CDK19 gene, a component of the mediator co-activator complex, has been linked to a human disease.

Lissencephaly and mild cerebellar vermis hypoplasia in a case of microcephaly and chorioretinal dysplasia

PURPOSE

Microcephaly and chorioretinal dysplasia is a very rare syndrome, characterized by microcephaly, chorioretinal dysplasia, mental retardation, and is phenotypically classified according to the presence of lymphedema. Among previously described patients, there has been no association with brain anomaly other than simple microcephaly, except for one case that presented with micro-lissencephaly, who had lymphedema.

METHODS

Herein, we describe a case of microcephaly and chorioretinal dysplasia without lymphedema who was shown to have lissencephaly and cerebellar vermis hypoplasia. His head circumference at birth was 28 cm (below -3SD) and both fundi showed pigmentary retinopathy with multiple punched-out lesions and retinal vascular attenuation.

RESULTS

Magnetic resonance imaging of the brain showed lissencephaly accompanied by inferior cerebellar vermis hypoplasia.

CONCLUSIONS

These results show that microcephaly and chorioretinal dysplasia can be accompanied by lissencephaly, thus brain imaging should be considered in evaluating these patients.