RPL26 variants: a rare cause of Diamond-Blackfan Anemia Syndrome with multiple congenital anomalies at the forefront.

PURPOSE: Diamond-Blackfan Anemia Syndrome (DBS) is a rare congenital disorder originally characterized by bone marrow failure with or without various congenital anomalies. At least 24 genes are implicated, the vast majority encoding for ribosomal proteins. RPL26 (ribosomal protein L26) is an emerging candidate (DBA11, MIM#614900). We aim to further delineate this rare condition. METHODS: Patients carrying heterozygous RPL26 variants were recruited. In one of them, erythroid proliferation and differentiation from peripheral blood CD34+ cells were studied by flow cytometry, and RPL26 expression by qRT-PCR and immunoblotting. RESULTS: We report on eight affected patients from four families. Detailed phenotyping reveals that RPL26 is mainly associated with multiple congenital anomalies (particularly radial ray anomalies), albeit with variable expression. Mandibulofacial dysostosis and neural tube defects are potential features in DBA11, expanding the growing list of DBS abnormalities. In one individual, we showed that RPL26 haploinsufficiency was responsible for subclinical impairment in erythroid proliferation and enucleation. The absence of hematological involvement in four adults from this series contributes to the mounting evidence that bone marrow failure is not universally central to all DBS genes. CONCLUSION: We confirm RPL26 as a DBS gene and expand the phenotypic spectrum of the gene and the disease.

A typical variant in TCF4 exon 18 is not associated with Pitt-Hopkins syndrome but with a familial case of mild and nonspecific neurodevelopmental disorder.

TCF4 gene encodes a class I helix-loop-helix transcription factor critical for the developing brain. Common polymorphisms in TCF4 and disruptive variants in the proximal region of the gene have been linked to relatively mild neuropsychiatric or neurodevelopmental disorders. In contrast, variants impacting distal exons are associated with Pitt-Hopkins syndrome (PTHS), a severe autosomal dominant condition characterized by profound intellectual disability, developmental delay, limited or absent speech, distinctive facies, and disordered breathing. Although phenotypic variability has been observed in PTHS, intellectual impairment and significant speech and motor delays are invariably present. In contrast to the typical de novo variants causing TCF4-related disorder and PTHS, we report a familial form of TCF4-related disorder where the missense variant arose de novo in the father and was inherited by two of his children. Although this family's variant's position in exon 18 predicted a typical PTHS phenotype, none of the affected individuals met the clinical diagnostic criteria for PTHS suggested by Zollino et al. in the first international consensus statement (as in the study by Zollino et al. in 2019). Rather, the three affected family members exhibited remarkably variable and milder phenotypes than would have been predicted from the position of their TCF4 variant. Thus, the clinical spectrum of PTHS-associated TCF4 variants may be broader than previously reported.