Investigation of the most common clinical and imaging findings and the role of tubulin genes in the etiology of malformations of cortical development

Background and aim: The number of reports on the role of tubulin gene mutations (TUBA1A, TUBB2B, and TUBB3) in etiology of malformations of cortical development has peaked in recent years. We aimed to determine tubulin gene defects on a patient population with simple and complex malformations of cortical development, and investigate the relationship between tubulin gene mutations and disease phenotype. Materials and methods: We evaluated 47 patients with simple or complex malformations of cortical development, as determined by radiological examination, for demographic features, clinical findings and mutations on TUBA1A, TUBB2B, and TUBB3 genes. Results: According to the magnetic resonance imaging findings, 19 patients (40.5%) had simple malformations of cortical development and 28 (59.5%) patients had complex malformations of cortical development. Focal cortical dysplasia was the most common simple malformation, lissencephaly was the most common coexisting cortical malformation, and corpus callosum anomalies were the most common coexisting extracortical neurodevelopmental abnormalities. None of the patients had genetic alterations on TUBA1A, TUBB2B, and TUBB3 genes causing protein dysfunction. On the other hand, the frequencies of some polymorphisms were higher when compared to the literature. Conclusion: It is crucial to identify the etiology in patients with malformations of cortical development in order to provide appropriate genetic counseling and prenatal diagnosis. We consider that multicenter studies with higher patient numbers and also including other malformations of cortical development-related genes are required to determine underlying etiological factors of malformations of cortical development patients.

Phenotypic spectrum of CHARGE syndrome based on clinical characteristics

Background/aim: CHARGE syndrome is a rare autosomal dominant disease with multiple congenital anomalies and cognitive impairment, which is caused by mutations in the CHD7 gene. This study aimed to disclose the mild end of the phenotypic spectrum of CHARGE syndrome, which has a highly variable expressivity. Materials and methods: Twenty-one patients who had at least one of the major symptoms of CHARGE syndrome (coloboma, choanal atresia, characteristic ear anomalies, semicircular canal hypoplasia, and cranial nerve anomalies) were included in the study. All patients were tested for karyotype analysis and CHD7 gene mutation/deletion. Results: In the study population, 6 different mutations were detected in 5 patients, and 2 different polymorphisms were detected in the CHD7 gene in 3 patients. MLPA analysis of all coding exons of the CHD7 gene revealed no pathogenic deletion/duplication. Conclusion: CHARGE syndrome should be considered as a differential diagnosis to detect the mild end of the spectrum, even if the patient does not fit the criteria.

Identification of a novel frameshift heterozygous deletion in exon 8 of the PAX6 gene in a pedigree with aniridia.

Aniridia is a congenital, panocular abnormality which is characterized by partial or complete absence of iris and various degrees of iris hypoplasia. Mutations in the PAX6 gene are found in ~90% of cases with aniridia. The human PAX6 gene is located at chromosome 11p13 and encodes a transcriptional regulator that has crucial roles in the development of the eyes, central nervous system and pancreatic islets. The present study performed a clinical and genomic analysis of two families containing multiple cases of aniridia. All exons of the PAX6 gene of the probands were sequenced using the Sanger sequencing technique. A heterozygous non­stop mutation in exon 14 was identified in the first family, which has been previously reported for a different ophthalmological pathology. This mutation causes on­going translation of the mRNA into the 3'­untranslated region. In the second family, a novel frameshift heterozygous deletion in exon 8 was identified.