Biallelic splicing variants in the nucleolar 60S assembly factor RBM28 cause the ribosomopathy ANE syndrome

Alopecia, neurologic defects, and endocrinopathy (ANE) syndrome is a rare ribosomopathy known to be caused by a p.(Leu351Pro) variant in the essential, conserved, nucleolar large ribosomal subunit (60S) assembly factor RBM28. We report the second family of ANE syndrome to date and a female pediatric ANE syndrome patient. The patient presented with alopecia, craniofacial malformations, hypoplastic pituitary, and hair and skin abnormalities. Unlike the previously reported patients with the p.(Leu351Pro) RBM28 variant, this ANE syndrome patient possesses biallelic precursor messenger RNA (pre-mRNA) splicing variants at the 5 ' splice sites of exon 5 (AE5) and exon 8 (AE8) of RBM28 (NM_018077.2:c.[541+1_541+2delinsA]; [946G > T]). In silico analyses and minigene splicing experiments in cells indicate that each splice variant specifically causes skipping of its respective mutant exon. Because the AE5 variant results in an in-frame 31 amino acid deletion (p.(Asp150_Lys180del)) in RBM28 while the AE8 variant leads to a premature stop codon in exon 9, we predicted that the AE5 variant would produce partially functional RBM28 but the AE8 variant would not produce functional protein. Using a yeast model, we demonstrate that the AE5 variant does indeed lead to reduced overall growth and large subunit ribosomal RNA (rRNA) production and pre-rRNA processing. In contrast, the AE8 variant is comparably null, implying that the partially functional AE5 RBM28 protein enables survival but precludes correct development. This discovery further defines the underlying molecular pathology of ANE syndrome to include genetic variants that cause aberrant splicing in RBM28 pre-mRNA and highlights the centrality of nucleolar processes in human genetic disease.

Automated summary

Alopecia, neurologic defects, and endocrinopathy (ANE) syndrome is a rare ribosomopathy caused by a variant in the RBM28 gene. A new case of ANE syndrome was reported, with the patient exhibiting alopecia, craniofacial malformations, hypoplastic pituitary, and hair and skin abnormalities. This patient had biallelic splicing variants in RBM28, resulting in skipping of mutant exons and potentially impacting protein function.