Novel homozygousALX4mutation causing frontonasal dysplasia-2 in a patient with meningoencephalocele

A rare homozygous ALX4 mutation in a Bangladeshi girl with frontonasal dysplasia type-2 (FND2)

Background

Frontonasal dysplasia type-2(FND2), a rare phenotypically variable and heterogeneous developmental anomaly resulting from mutation of the ALX4 gene, is primarily characterized by malformation of the skull and facial skeleton. This study was designed to showcase a clinical, imaging, and genetic analysis of FND2 in a consanguineous family of Bangladeshi origin.

Methodology

Clinical imaging and whole genome sequencing of mother, father and patient was done by using Nextera DNA flex library preparation kit (Illumina, USA) using Novaseq 6000 next generation sequencer to find out ALX4 mutation which causes FND2 in patient.

Result

We report the clinical as well as molecular findings in an 8-year-old girl with FND2. The child presented with various characteristic features of skull and facial anomalies associated with FND 2 along with numerous other features many of which have not been described in previous literature. The parents also showed some key clinical, radiological, and genetic features of FND 2. The whole genome sequencing (WGS) revealed homozygosity for a 793C-T transition in the ALX4 gene, which resulted in premature termination at codon 265 (p.Arg265Ter). Both of her parents were heterozygous carriers of ALX4 mutation.

Conclusions

This is the first report that associates clinical, imaging, and genomics analyses in a Bangladeshi patient for better understanding the disease FND2. These results will facilitate diagnosis and genetic counseling of the future FND2 patients.

Identification of a novel homozygous ALX4 mutation in two unrelated patients with frontonasal dysplasia type-2

We report two unrelated boys with frontonasal dysplasias type-2 (FND-2) who shared an identical novel homozygous ALX4 mutation c.291delG (p.Q98Sfs*83). Both patients presented with a large skull defect but one had bilateral parietal meningocele-like cysts that lie along with the bony defect and increased in size with age. Scalp alopecia, hypertelorism, and clefted alae nasi were also detected in both of them. Furthermore, impalpable gonads were noted, being unilateral in one and bilateral in the other. Neuroimaging showed small dysplastic occipital lobes with dysgyria and midline subarachnoid cyst. Additional dysplastic corpus callosum and small cerebellar vermis were observed in one patient. Parietal foramina were noted in the parents of one patient. Our findings highlight the dosage effect of ALX4 and underscore the challenges of prenatal genetic counseling. Further, the indirect role of ALX4 in the development of the occipital lobe and posterior fossa is discussed.