De novo mutations in FBRSL1 cause a novel recognizable malformation and intellectual disability syndrome.

We report truncating de novo variants in specific exons of FBRSL1 in three unrelated children with an overlapping syndromic phenotype with respiratory insufficiency, postnatal growth restriction, microcephaly, global developmental delay and other malformations. The function of FBRSL1 is largely unknown. Interestingly, mutations in the FBRSL1 paralogue AUTS2 lead to an intellectual disability syndrome (AUTS2 syndrome). We determined human FBRSL1 transcripts and describe protein-coding forms by Western blot analysis as well as the cellular localization by immunocytochemistry stainings. All detected mutations affect the two short N-terminal isoforms, which show a ubiquitous expression in fetal tissues. Next, we performed a Fbrsl1 knockdown in Xenopus laevis embryos to explore the role of Fbrsl1 during development and detected craniofacial abnormalities and a disturbance in neurite outgrowth. The aberrant phenotype in Xenopus laevis embryos could be rescued with a human N-terminal isoform, while the long isoform and the N-terminal isoform containing the mutation p.Gln163* isolated from a patient could not rescue the craniofacial defects caused by Fbrsl1 depletion. Based on these data, we propose that the disruption of the validated N-terminal isoforms of FBRSL1 at critical timepoints during embryogenesis leads to a hitherto undescribed complex neurodevelopmental syndrome.

CANPMR syndrome and chromosome 1p32-p31 deletion syndrome coexist in two related individuals affected by simultaneous haplo-insufficiency of CAMTA1 and NIFA genes.

BACKGROUND: Non-progressive cerebellar ataxia with mental retardation (CANPMR, OMIM 614756) and chromosome 1p32-p31 deletion syndrome (OMIM 613735) are two very rare inherited disorders, which are caused by mono-allelic deficiency (haplo-insufficiency) of calmodulin-binding transcription activator 1 (CAMTA1) and, respectively, nuclear factor 1 A (NFIA) genes. The yet reported patients affected by mono-allelic CAMTA1 dysfunction presented with neonatal hypotonia, delayed and ataxic gait, cerebellar atrophy, psychological delay and speech impairment, while individuals carrying a disrupted NFIA allele suffered from agenesis/hypoplasia of the corpus callosum, ventriculomegaly, developmental delay and urinary tract abnormalities. Both disorders were not seen in one patient together before. RESULTS: In this study two related individuals affected by a complex clinical syndrome, characterized by cognitive, neurological and nephrological features were studied for the underlying genetic disorder(s) by molecular cytogenetics. The two individuals present dysmorphic facies, macrocephaly, generalized ataxia, mild tremor, strabismus, mild mental retardation and kidney hypoplasia. Moreover, neuro-radiological studies showed hypoplasia of corpus callosum. Genetic investigations revealed a paracentric inversion in the short arm of one chromosome 1 with breakpoints within CAMTA1 and NFIA coding sequences. CONCLUSIONS: To the best of our knowledge, this is the first report of two patients harboring the simultaneous mono-allelic disruptions and consequent haplo-insufficiencies of two genes due to an inversion event. Disruption of CAMTA1 and NFIA genes led to neuro-psychological and nephrological dysfunctions, which comprised clinical features of CANPMR syndrome as well as chromosome 1p32-p31 deletion syndrome.