A persistent variant telomere sequence in a human pedigree.

The telomere sequence, TTAGGG, is conserved across all vertebrates and plays an essential role in suppressing the DNA damage response by binding a set of proteins termed shelterin. Changes in the telomere sequence impair shelterin binding, initiate a DNA damage response, and are toxic to cells. Here we identify a family with a variant in the telomere template sequence of telomerase, the enzyme responsible for telomere elongation, that led to a non-canonical telomere sequence. The variant is inherited across at least one generation and one family member reports no significant medical concerns despite ~9% of their telomeres converting to the novel sequence. The variant template disrupts telomerase repeat addition processivity and decreased the binding of the telomere-binding protein POT1. Despite these disruptions, the sequence is readily incorporated into cellular chromosomes. Incorporation of a variant sequence prevents POT1-mediated inhibition of telomerase suggesting that incorporation of a variant sequence may influence telomere addition. These findings demonstrate that telomeres can tolerate substantial degeneracy while remaining functional and provide insights as to how incorporation of a non-canonical telomere sequence might alter telomere length dynamics.

A novel IKZF1 variant in a family with autosomal dominant CVID: A case for expanding exon coverage in inborn errors of immunity.

Common variable immune deficiency (CVID) is a heterogenous group of disorders characterized by varying degrees of hypogammaglobulinemia, recurrent infections, and autoimmunity. Currently, pathogenic variants are identified in approximately 20-30% of CVID cases. Here we report a 3-generation family with autosomal dominant Common Variable Immunodeficiency (CVID) diagnosed in 9 affected individuals. Although primary immune deficiency panels and exome sequencing were non-diagnostic, whole genome sequencing revealed a novel, pathogenic c.499C > T: p.His167Tyr variant in IKZF1, a critical regulator of B cell development. Functional testing done through pericentromeric heterochromatin localization and light shift chemiluminescent electrophoretic mobility shift assay confirmed the variant's deleterious effect via a haploinsufficiency mechanism. Our findings expand the spectrum of known IKZF1 mutations and contribute to a more comprehensive understanding of CVID's genetic heterogeneity. Furthermore, this case underscores the importance of considering whole genome sequencing for comprehensive genetic diagnosis when concern for a monogenic inborn errors of immunity is high.

IKAROS-how many feathers have you lost: mild and severe phenotypes in IKZF1 deficiency.

Heterozygous germline variants in human IKZF1 encoding for IKAROS define an inborn error of immunity with immunodeficiency, immune dysregulation and risk of malignancy with a broad phenotypic spectrum. Growing evidence of underlying pathophysiological genotype-phenotype correlations helps to improve our understanding of IKAROS-associated diseases. We describe 6 patients from 4 kindreds with two novel IKZF1 variants leading to haploinsufficiency from 3 centers in Germany. We also provide an overview of first symptoms to a final diagnosis including data from the literature.

Disease-associated AIOLOS variants lead to immune deficiency/dysregulation by haploinsufficiency and redefine AIOLOS functional domains.

AIOLOS, also known as IKZF3, is a transcription factor that is highly expressed in the lymphoid lineage and is critical for lymphocyte differentiation and development. Here, we report on 9 individuals from 3 unrelated families carrying AIOLOS variants Q402* or E82K, which led to AIOLOS haploinsufficiency through different mechanisms of action. Nonsense mutant Q402* displayed abnormal DNA binding, pericentromeric targeting, posttranscriptional modification, and transcriptome regulation. Structurally, the mutant lacked the AIOLOS zinc finger (ZF) 5-6 dimerization domain, but was still able to homodimerize with WT AIOLOS and negatively regulate DNA binding through ZF1, a previously unrecognized function for this domain. Missense mutant E82K showed overall normal AIOLOS functions; however, by affecting a redefined AIOLOS protein stability domain, it also led to haploinsufficiency. Patients with AIOLOS haploinsufficiency showed hypogammaglobulinemia, recurrent infections, autoimmunity, and allergy, but with incomplete clinical penetrance. Altogether, these data redefine the AIOLOS structure-function relationship and expand the spectrum of AIOLOS-associated diseases.

TPP1 promoter mutations cooperate with TERT promoter mutations to lengthen telomeres in melanoma.

Overcoming replicative senescence is an essential step during oncogenesis, and the reactivation of TERT through promoter mutations is a common mechanism. TERT promoter mutations are acquired in about 75% of melanomas but are not sufficient to maintain telomeres, suggesting that additional mutations are required. We identified a cluster of variants in the promoter of ACD encoding the shelterin component TPP1. ACD promoter variants are present in about 5% of cutaneous melanoma and co-occur with TERT promoter mutations. The two most common somatic variants create or modify binding sites for E-twenty-six (ETS) transcription factors, similar to mutations in the TERT promoter. The variants increase the expression of TPP1 and function together with TERT to synergistically lengthen telomeres. Our findings suggest that TPP1 promoter variants collaborate with TERT activation to enhance telomere maintenance and immortalization in melanoma.