The impact of 22q11.2 copy-number variants on human traits in the general population.

While extensively studied in clinical cohorts, the phenotypic consequences of 22q11.2 copy-number variants (CNVs) in the general population remain understudied. To address this gap, we performed a phenome-wide association scan in 405,324 unrelated UK Biobank (UKBB) participants by using CNV calls from genotyping array. We mapped 236 Human Phenotype Ontology terms linked to any of the 90 genes encompassed by the region to 170 UKBB traits and assessed the association between these traits and the copy-number state of 504 genotyping array probes in the region. We found significant associations for eight continuous and nine binary traits associated under different models (duplication-only, deletion-only, U-shape, and mirror models). The causal effect of the expression level of 22q11.2 genes on associated traits was assessed through transcriptome-wide Mendelian randomization (TWMR), revealing that increased expression of ARVCF increased BMI. Similarly, increased DGCR6 expression causally reduced mean platelet volume, in line with the corresponding CNV effect. Furthermore, cross-trait multivariable Mendelian randomization (MVMR) suggested a predominant role of genuine (horizontal) pleiotropy in the CNV region. Our findings show that within the general population, 22q11.2 CNVs are associated with traits previously linked to genes in the region, and duplications and deletions act upon traits in different fashions. We also showed that gain or loss of distinct segments within 22q11.2 may impact a trait under different association models. Our results have provided new insights to help further the understanding of the complex 22q11.2 region.

Single cell multi-omic analysis identifies a Tbx1-dependent multilineage primed population in murine cardiopharyngeal mesoderm.

The poles of the heart and branchiomeric muscles of the face and neck are formed from the cardiopharyngeal mesoderm within the pharyngeal apparatus. They are disrupted in patients with 22q11.2 deletion syndrome, due to haploinsufficiency of TBX1, encoding a T-box transcription factor. Here, using single cell RNA-sequencing, we now identify a multilineage primed population within the cardiopharyngeal mesoderm, marked by Tbx1, which has bipotent properties to form cardiac and branchiomeric muscle cells. The multilineage primed cells are localized within the nascent mesoderm of the caudal lateral pharyngeal apparatus and provide a continuous source of cardiopharyngeal mesoderm progenitors. Tbx1 regulates the maturation of multilineage primed progenitor cells to cardiopharyngeal mesoderm derivatives while restricting ectopic non-mesodermal gene expression. We further show that TBX1 confers this balance of gene expression by direct and indirect regulation of enriched genes in multilineage primed progenitors and downstream pathways, partly through altering chromatin accessibility, the perturbation of which can lead to congenital defects in individuals with 22q11.2 deletion syndrome.

Lymphoproliferative disorder with polyautoimmunity and hypogammaglobulinemia: An unusual presentation of 22q11.2 deletion syndrome.

22q11.2 deletion syndrome (22q11.2DS) has a heterogeneous presentation that includes multiple congenital anomalies and immunodeficiency, one of the most striking features. Usually, it is characterized by T cell lymphopenia, B cell dysfunction and autoimmunity. Here, we describe an unusual case of 22q11.2DS in a patient with lymphoproliferative disorder, polyautoimmunity and hypogammaglobulinemia.

Wolf-Hirschhorn Syndrome with Epibulbar Dermoid: An Unusual Association in a Patient with 4p Deletion and Functional Xp Disomy.

Wolf-Hirschhorn syndrome (WHS) is a contiguous gene and multiple malformation syndrome that results from a deletion in the 4p16.3 region. We describe here a 6-month-old girl that presented with WHS features but also displayed unusual findings, such as epibulbar dermoid in the left eye, ear tags, and left microtia. Although on G-banding her karyotype appeared to be normal, chromosomal microarray analysis revealed an ∼13-Mb 4p16.3p15.33 deletion and an ∼9-Mb Xp22.33p22.31 duplication, resulting from a balanced maternal t(X;4)(p22.31;p15.33) translocation. The patient presented with functional Xp disomy due to an unbalanced X-autosome translocation, a rare cytogenetic finding in females with unbalanced rearrangements. Sequencing of both chromosome breakpoints detected no gene disruption. To the best of our knowledge, this is the first patient described in the literature with WHS and epibulbar dermoid, a typical characteristic of the oculoauriculovertebral spectrum (OAVS). Our data suggest that possible candidate genes for OAVS may have been deleted along with the WHS critical region.

Atypical 581-kb 22q11.21 Deletion in a Patient with Oculo-Auriculo-Vertebral Spectrum Phenotype.

The oculo-auriculo-vertebral spectrum (OAVS) is defined as a group of malformations involving the ears, mouth, mandible, eyes, and cervical spine. Establishing an accurate clinical diagnosis of OAVS is a challenge for clinical geneticists, not only because these patients display heterogeneous phenotypes, but also because its etiology encompasses environmental factors, unknown genetic factors and different chromosome aberrations. To date, several chromosomal abnormalities have been associated with the syndrome, most frequently involving chromosome 22. In the literature, six 22q11.2 microdeletions have been described within the same region, suggesting possible OAVS candidate genes in this segment. Here, we report on a patient with an ∼581-kb 22q11.21 deletion, detected by genomic array and MLPA. This is the 7th case described with OAVS and 22q deletion, suggesting that the 22q11.2 region may be related to the regulation of body symmetry and facial development.