Motahari et al. Journal of Neurodevelopmental Disorders (2019) 11:7 https://doi.org/10.1186/s11689-019-9267-z REVIEW Open Access In the line-up: deleted genes associated with DiGeorge/22q11.2 deletion syndrome: are they all suspects? Zahra Motahari, Sally Ann Moody, Thomas Michael Maynard and Anthony-Samuel LaMantia* Abstract Background: 22q11.2 deletion syndrome (22q11DS), a copy number variation(CNV)disorder,occursinapproximately 1:4000 live births due to a heterozygous microdeletion at position 11.2 (proximal) on the q arm of human chromosome 22 (hChr22) (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011). This disorder was known as DiGeorge syndrome, Velo-cardio-facial syndrome (VCFS) or conotruncal anomaly face syndrome (CTAF) based upon diagnostic cardiovascular, pharyngeal, and craniofacial anomalies (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011; Burn et al., J Med Genet 30:822-4, 1993) before this phenotypic spectrum was associated with 22q11.2 CNVs. Subsequently, 22q11.2 deletion emerged as a major genomic lesion associated with vulnerability for several clinically defined behavioral deficits common to a number of neurodevelopmental disorders (Fernandez et al., Principles of Developmental Genetics, 2015; Robin and Shprintzen, J Pediatr 147:90-6, 2005; Schneider et al., Am J Psychiatry 171:627-39, 2014). Results: The mechanistic relationships between heterozygously deleted 22q11.2 genes and 22q11DS phenotypes are still unknown. We assembled a comprehensive “line-up” of the 36 protein coding loci in the 1.5 Mb minimal critical deleted region on hChr22q11.2, plus 20 protein coding loci in the distal 1.5 Mb that defines the 3 Mb typical 22q11DS deletion. We categorized candidates based upon apparent primary cell biological functions. We analyzed 41 of these genes that encode known proteins to determine whether haploinsufficiency of any single 22q11.2 gene—a one gene to one phenotype correspondence due to heterozygous deletion restricted to that locus—versus complex multigenic interactions can account for single or multiple 22q11DS phenotypes. Conclusions: Our 22q11.2 functional genomic assessment does not support current theories of single gene haploinsufficiency for one or all 22q11DS phenotypes. Shared molecular functions, convergence on fundamental cell biological processes, and related consequences of individual 22q11.2 genes point to a matrix of multigenic interactions due to diminished 22q11.2 gene dosage. These interactions target fundamental cellular mechanisms essential for development, maturation, or homeostasis at subsets of 22q11DS phenotypic sites. Keywords: 22q11DS, Neural development, Cognition, Cardiovascular, Craniofacial, Copy number variants, Polygenic Background define the region (Fig. 1a) [6].TheseLCRs,duetosubstan- The frequency of 22q11.2 deletion—the chromosomal/copy tial sequence similarity, facilitate non-allelic homologous number variant (CNV) that results in most cases of meiotic recombination, or “deletion by crossing over of DiGeorge/22q11DS [1, 2]—reflects the unusual genomic repetitive DNA” [7], resulting in unbalanced translocation, architecture of human chromosome 22 (hChr22), position deletions, or duplication [8]. More than 85% of recombi- q11.2. At least four repetitive DNA “cassettes” known as nation occurs between LCR A and LCR D resulting in a low copy-number repeats (LCRs): LCR A, B, C, and D; 3Mb“typical” deletion. The smaller 1.5 Mb “minimal critical” deletion, occurs between LCR A and LCR B in * Correspondence: [email protected] ∼ 10% of affected individuals [6, 8]. Deleted individuals The Institute for Neuroscience, and Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health have complex and variable phenotypes including de- Sciences, Washington DC 20037, USA velopmental delay, congenital heart defects, craniofacial © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Motahari et al. Journal of Neurodevelopmental Disorders (2019) 11:7 Page 2 of 28 Fig. 1 Genes deleted in 22q11DS. a Schematic of the 22q11.2 region. Low copy repeats (LCRs) are shown as gray boxes: LCR A-D (not to scale). b Protein-coding genes (n = 56) are color-coded based on primary, putative, or family member functions as eleven groups. c mRNA (Prodh, Zdhhc8, Sept5, Gnb1l, Ranbp1, Dgcr8, Arvcf, Dgcr2,andTrmt2a) or protein (Ufd1l, Hira, Comt) expression of selected genes at mouse embryonic stageE10.5[58, 73, 169]. d Expression localization of Cdc45, Ranbp1,andSept5 in the entire cortical hemisphere of E14.5 embryos (left) and in a higher magnification (right) [60]. Expression pattern of Zdhhc8 is shown in the adult cerebellum (left) and the cortex (right) [310]. Immunolocalization of Ufd1l and Comt proteins in the hippocampus (left) and cerebellum (right) of the adult mouse brain are shown [58]. VZ ventricular zone, IZ intermediate zone, CP cortical plate, gc granular cell layer, P purkinje cell layer, ml molecular layer, Cb cerebellum, Ctx cortex. Hip hippocampus, Calb calbindin. Scale bars: Cdc45, Ranbp1, Sept5 =250μm, insets = 6.6x, Zdhhc8 =50μm(left)and100μm (right). Ufd/Comt: hippocampus (upper left) = 250 μm, insets (lower left) = 10x, cerebellum (right) = 25 μm anomalies such as cleft palate and retrognathia, muscu- 22q11.2 deletion syndrome (22q11DS) is associated loskeletal anomalies, eye anomalies, hearing loss, absent with behavioral and psychiatric complications such as or small thymus and parathyroid glands, hypocalcemia, schizophrenia (SCZ) autistic spectrum disorders (ASD), compromised immune system, feeding difficulties, and attention deficit hyperactivity disorder (ADHD), anxiety seizures. In addition to these physical manifestations, disorder, as well as intellectual and learning disabilities Motahari et al. Journal of Neurodevelopmental Disorders (2019) 11:7 Page 3 of 28 [3–5]. Clearly, the range of genomic lesions, numbers supports polygenic inheritance of broader, clinically defined of genes, and spectrum of phenotypes that define behavioral disorders. In ASD, aside from 22q11.2, five 22q11 CNV disorders defies straightforward expla- additional CNV loci: 1q21.1, 3q29, 7q11.23, 16p11.2, nations of genotype to phenotype correlations. The and 15q11.2–13, as well as multiple de novo gene va- essential question remains: how CNVs of one, many, or riants have been identified as risk factors [21]. Similarly, all 22q11.2 genes disrupts developmental and homeo- SCZ is associated with multiple, rare loss and gain of static mechanisms and complicates the lives of children function mutations in genes that encode calcium chan- and adults with 22q11DS. nels, postsynaptic cytoskeleton-associated scaffold pro- Individuals with the AtoBdeletion (we use this no- teins, and cell adhesion/signaling molecules [22, 23]. menclature to identify heterozygous elimination of Whole exome sequence analyses in individuals with 22q11.2 genes between LCRs A and B) have the full non-syndromic congenital heart defects also fail to sup- spectrum of phenotypes seen also with the typical Ato port robust individual gene/phenotype correlations D deletion (i.e., elimination of genes between LCRs A [24]. It is thus unlikely that developmental phenotypes and D), suggesting that key 22q11DS phenotypes are in individuals with 22q11.2 CNVs—including com- largely due to diminished AtoBgene dosage [9–11]. monly diagnosed behavioral deficits associated with Microcephaly and ocular anomalies occur in about 50% neurodevelopmental disorders—arise from the con- of individuals with AtoBor AtoDdeletions compared sequences of altered dosage of one single gene within the to 7% in BtoDor CtoDdeleted individuals, and AtoDregion. Indeed, single gene explanation for indi- cardiovascular defects also appear to be > 3 times more vidual phenotypes or complete phenotypic spectra are frequent in AtoBor AtoDdeletions [12]. Neverthe- unlikely for most CNV syndromes, including fairly less, deletions in distal regions, BtoDor CtoD, have common deletions and duplications at 7q11.23 (Williams been associated with cardiac developmental anomalies Syndrome), 15q11.2 (Prader-Willi Angelman Syndrome), similar to those associated with AtoBor AtoDdele- 16p11.2 (Autism Susceptibility), and even whole or partial tions, albeit with lower frequency [13]. Furthermore, the chromosomal anomalies like trisomy 21 (Down syn- presence and severity of phenotypes among individuals drome). Thus, a reassessment of the known protein carrying the AtoBdeletion [14] varies significantly, coding genes at 22q11.2 between LCRs A and D, and their even in siblings who inherit the same deletion from a causal relationship to 22q11DS, based upon a thorough 22q11.2-deleted parent [15]. In the context of these review of molecular and cellular mechanisms through complex associations between penetrance and severity, it which each gene influences development or ongoing is unlikely that haploinsufficiency of TBX1 (a 22q11.2 A physiological function, is necessary, timely, and may have to B gene