Interstitial deletion 1q42 in a patient with agenesis of corpus callosum: Phenotype-genotype comparison to the 1q41q42 microdeletion suggests a contiguous 1q4 syndrome

Case Report: Identification of a de novo Microdeletion 1q44 in a Patient With Seizures and Developmental Delay

Objective: 1q44 microdeletion syndrome is difficult to diagnose due to the wide phenotypic spectrum and strong genetic heterogeneity. We explore the correlation between the chromosome microdeletions and phenotype in a child with 1q44 microdeletion syndrome, we collected the clinical features of the patient and combined them with adjacent copy number variation (CNV) regions previously reported.

Methods: We collected the full medical history of the patient and summarized her clinical symptoms. Whole-exome sequencing (WES) and CapCNV analysis were performed with DNA extracted from both the patient's and her parents' peripheral blood samples. Fluorescent quantitative PCR (q-PCR) was performed for the use of verification to the CNV regions.

Results: A 28.7 KB microdeletion was detected in the 1q44 region by whole-exome sequencing and low-depth whole-genome sequencing. The deleted region included the genes COX20 and HNRNPU. As verification, karyotype analysis showed no abnormality, and the results of qPCR were consistent with that of whole-exome sequencing and CapCNV analysis.

Conclusion: The patient was diagnosed with 1q44 microdeletion syndrome with clinical and genetic analysis. Analyzing both whole-exome sequencing and CapCNV analysis can not only improve the diagnostic rate of clinically suspected syndromes that present with intellectual disability (ID) and multiple malformations but also support further study of the correlation between CNVs and clinical phenotypes. This study lays the foundation for the further study of the pathogenesis of complex diseases.

1q42.12q42.2 Deletion in a Child with Midline Defects and Hypoplasia of the Corpus Callosum

Chromosome 1q42.12q42.2 deletions are documented as "disease causing" and show overlapping phenotypes depending on the genes involved in the deletion. In this report, we detected a 5.8-Mb deletion encompassing the chromosome 1q42.12q42.2 region in a 4-year-old boy with hypoplastic corpus callosum, epilepsy, developmental delay, microcephaly, cataract, cleft palate, and skeletal changes. The deletion was de novo. Genotype-phenotype correlations suggest that the major features of 1q42.12q42.2 microdeletion were attributed to the genes with a high probability of loss-of-function intolerance score in this deletion, namely LBR, ENAH, ACBD3, LIN9, ITPKB, CDC42BPA, ARF1, TAF5L, GALNT2, SPRTN, and EGLN1 along with GNPAT.

Phenotypic features of 1q41q42 microdeletion including WDR26 and FBXO28 are clinically recognizable: The first case from Japan

1q41q42 microdeletion syndrome has been established in 2007. Since then, more than 17 patients have been reported so far. The reported deletions showed random breakpoints and deletion regions are aligned as roof tiles. Patients with 1q41q42 microdeletion syndrome show intellectual disability, seizures, and distinctive features. Many genotype-phenotype correlation studies have been performed and some genes included in this region have been suggested as potential candidate genes. Recently, de novo variants in WDR26 and FBXO28 were identified in patients who showed consistent phenotypes with 1q41q42 microdeletion syndrome. Thus, both genes are now considered as the genes possibly responsible for 1q41q42 microdeletion syndrome. Here, the first case of a Japanese patient with a de novo 1q41q42 microdeletion is reported. Owing to the distinctive features, this syndrome would be clinically recognizable.

WDR26 Haploinsufficiency Causes a Recognizable Syndrome of Intellectual Disability, Seizures, Abnormal Gait, and Distinctive Facial Features

We report 15 individuals with de novo pathogenic variants in WDR26. Eleven of the individuals carry loss-of-function mutations, and four harbor missense substitutions. These 15 individuals comprise ten females and five males, and all have intellectual disability with delayed speech, a history of febrile and/or non-febrile seizures, and a wide-based, spastic, and/or stiff-legged gait. These subjects share a set of common facial features that include a prominent maxilla and upper lip that readily reveal the upper gingiva, widely spaced teeth, and a broad nasal tip. Together, these features comprise a recognizable facial phenotype. We compared these features with those of chromosome 1q41q42 microdeletion syndrome, which typically contains WDR26, and noted that clinical features are consistent between the two subsets, suggesting that haploinsufficiency of WDR26 contributes to the pathology of 1q41q42 microdeletion syndrome. Consistent with this, WDR26 loss-of-function single-nucleotide mutations identified in these subjects lead to nonsense-mediated decay with subsequent reduction of RNA expression and protein levels. We derived a structural model of WDR26 and note that missense variants identified in these individuals localize to highly conserved residues of this WD-40-repeat-containing protein. Given that WDR26 mutations have been identified in ∼1 in 2,000 of subjects in our clinical cohorts and that WDR26 might be poorly annotated in exome variant-interpretation pipelines, we would anticipate that this disorder could be more common than currently appreciated.

Identification of a de novo microdeletion 1q44 in a patient with hypogenesis of the corpus callosum, seizures and microcephaly - A case report

Microdeletion 1q44 on the long arm of chromosome 1 leads to a phenotype that includes microcephaly, seizure, agenesis or hypogenesis of the corpus callosum, polydactyly, congenital heart defects and severe developmental delay along with characteristic facial dysmorphic signs. Until today, the distinct genetic causes for the different symptoms remain unclear. We here report a 1.2Mb de novo microdeletion 1q44 identified by performing a SNP array analysis. The female patient presented with microcephaly, seizure, hypogenesis of corpus callosum, postaxial hexadactyly, an atrial septal defect, a ventricular septal defect, hypertelorism, a long and smooth philtrum, thin vermilion borders, and micrognathia, all common features of microdeletion 1q44. An additionally performed chromosome analysis excluded any chromosomal rearrangements. The deleted region included the genes ZBTB18 as well as HNRNPU amongst others. Both are possibly candidate genes for the dysgenesis of the corpus callosum. AKT3, another candidate gene, was not affected by the deletion in this patient. Thus, the genetic findings in this case report spotlight ZBTB18 and HNRNPU in the genesis of the typical microdeletion 1q44 symptoms, especially concerning the dysgenesis of the corpus callosum, and therefore could help to unveil more of the genetic background of this syndrome.

Psychomotor retardation with a 1q42.11-q42.12 deletion

A 1q42 deletion is a rare structure variation that commonly harbours various deletion breakpoints along with diversified phenotypes. In our study, we found a de novo 1q42 deletion in a boy who did not have a cleft palate or a congenital diaphragmatic hernia but presented with psychomotor retardation. A 1.9 Mb deletion located within 1q42.11-q42.12 was validated at the molecular cytogenetic level. This is the first report of a 1q42.11-q42.12 deletion in a patient with onlypsychomotor retardation. The precise break points could facilitate the discovery of potential causative genes, such as LBR, EPHX1, etc. The correlation between the psychomotor retardation and the underlying genetic factors could not only shed light on the diagnosis of psychomotor retardation at the genetic level but also provide potential therapeutic targets.

ASPP2 deficiency causes features of 1q41q42 microdeletion syndrome

Chromosomal abnormalities are implicated in a substantial number of human developmental syndromes, but for many such disorders little is known about the causative genes. The recently described 1q41q42 microdeletion syndrome is characterized by characteristic dysmorphic features, intellectual disability and brain morphological abnormalities, but the precise genetic basis for these abnormalities remains unknown. Here, our detailed analysis of the genetic abnormalities of 1q41q42 microdeletion cases identified TP53BP2, which encodes apoptosis-stimulating protein of p53 2 (ASPP2), as a candidate gene for brain abnormalities. Consistent with this, Trp53bp2-deficient mice show dilation of lateral ventricles resembling the phenotype of 1q41q42 microdeletion patients. Trp53bp2 deficiency causes 100% neonatal lethality in the C57BL/6 background associated with a high incidence of neural tube defects and a range of developmental abnormalities such as congenital heart defects, coloboma, microphthalmia, urogenital and craniofacial abnormalities. Interestingly, abnormalities show a high degree of overlap with 1q41q42 microdeletion-associated abnormalities. These findings identify TP53BP2 as a strong candidate causative gene for central nervous system (CNS) defects in 1q41q42 microdeletion syndrome, and open new avenues for investigation of the mechanisms underlying CNS abnormalities.

A 11.7-Mb Paracentric Inversion in Chromosome 1q Detected in Prenatal Diagnosis Associated with Familial Intellectual Disability

Most apparent balanced chromosomal inversions are usually clinically asymptomatic; however, infertility, miscarriages, and mental retardation have been reported in inversion carriers. We present a small family with a paracentric inversion 1q42.13q43 detected in routine prenatal diagnosis. Molecular cytogenetic methods defined the size of the inversion as 11.7 Mb and excluded other unbalanced chromosomal alterations in the patients. Our findings suggest that intellectual disability is caused by dysfunction, disruption, or position effects of genes located at or near the breakpoints involved in this inversion.

The mammalian molybdenum enzymes of mARC

The "mitochondrial amidoxime reducing component" (mARC) is the most recently discovered molybdenum-containing enzyme in mammals. All mammalian genomes studied to date contain two mARC genes: MARC1 and MARC2. The proteins encoded by these genes are mARC-1 and mARC-2 and represent the simplest form of eukaryotic molybdenum enzymes, only binding the molybdenum cofactor. In the presence of NADH, mARC proteins exert N-reductive activity together with the two electron transport proteins cytochrome b5 type B and NADH cytochrome b5 reductase. This enzyme system is capable of reducing a great variety of N-hydroxylated substrates. It plays a decisive role in the activation of prodrugs containing an amidoxime structure, and in detoxification pathways, e.g., of N-hydroxylated purine and pyrimidine bases. It belongs to a group of drug metabolism enzymes, in particular as a counterpart of P450 formed N-oxygenated metabolites. Its physiological relevance, on the other hand, is largely unknown. The aim of this article is to summarize our current knowledge of these proteins with a special focus on the mammalian enzymes and their N-reductive activity.

New microdeletion and microduplication syndromes: A comprehensive review

Several new microdeletion and microduplication syndromes are emerging as disorders that have been proven to cause multisystem pathologies frequently associated with intellectual disability (ID), multiple congenital anomalies (MCA), autistic spectrum disorders (ASD) and other phenotypic findings. In this paper, we review the "new" and emergent microdeletion and microduplication syndromes that have been described and recognized in recent years with the aim of summarizing their main characteristics and chromosomal regions involved. We decided to group them by genomic region and within these groupings have classified them into those that include ID, MCA, ASD or other findings. This review does not intend to be exhaustive but is rather a quick guide to help pediatricians, clinical geneticists, cytogeneticists and/or molecular geneticists.

Clinical, genetic and imaging findings identify new causes for corpus callosum development syndromes

The corpus callosum is the largest fibre tract in the brain, connecting the two cerebral hemispheres, and thereby facilitating the integration of motor and sensory information from the two sides of the body as well as influencing higher cognition associated with executive function, social interaction and language. Agenesis of the corpus callosum is a common brain malformation that can occur either in isolation or in association with congenital syndromes. Understanding the causes of this condition will help improve our knowledge of the critical brain developmental mechanisms required for wiring the brain and provide potential avenues for therapies for callosal agenesis or related neurodevelopmental disorders. Improved genetic studies combined with mouse models and neuroimaging have rapidly expanded the diverse collection of copy number variations and single gene mutations associated with callosal agenesis. At the same time, advances in our understanding of the developmental mechanisms involved in corpus callosum formation have provided insights into the possible causes of these disorders. This review provides the first comprehensive classification of the clinical and genetic features of syndromes associated with callosal agenesis, and provides a genetic and developmental framework for the interpretation of future research that will guide the next advances in the field.

DISC1 genetics, biology and psychiatric illness

Psychiatric disorders are highly heritable, and in many individuals likely arise from the combined effects of genes and the environment. A substantial body of evidence points towards DISC1 being one of the genes that influence risk of schizophrenia, bipolar disorder and depression, and functional studies of DISC1 consequently have the potential to reveal much about the pathways that lead to major mental illness. Here, we review the evidence that DISC1 influences disease risk through effects upon multiple critical pathways in the developing and adult brain.

Clinical impact of copy number variation analysis using high-resolution microarray technologies: advantages, limitations and concerns

Copy number variation (CNV) analysis has had a major impact on the field of medical genetics, providing a mechanism to identify disease-causing genomic alterations in an unprecedented number of diseases and phenotypes. CNV analysis is now routinely used in the clinical diagnostic laboratory, and has led to a significant increase in the detection of chromosomal abnormalities. These findings are used for prenatal decision making, clinical management and genetic counseling. Although a powerful tool to identify genomic alterations, CNV analysis may also result in the detection of genomic alterations that have unknown clinical significance or reveal unintended information. This highlights the importance of informed consent and genetic counseling for clinical CNV analysis. This review examines the advantages and limitations of CNV discovery in the clinical diagnostic laboratory, as well as the impact on the clinician and family.

High resolution array in the clinical approach to chromosomal phenotypes

Array genomic hybridization (AGH) has recently been implemented as a diagnostic tool for the detection of submicroscopic copy number variants (CNVs) in patients with developmental disorders. However, there is no consensus regarding the choice of the platform, the minimal resolution needed and systematic interpretation of CNVs. We report our experience in the clinical diagnostic use of high resolution AGH up to 100 kb on 131 patients with chromosomal phenotypes but previously normal karyotype. We evaluated the usefulness in our clinics and laboratories by the detection rate of causal CNVs and CNVs of unknown clinical significance and to what extent their interpretation would challenge the systematic use of high-resolution arrays in clinical application. Prioritizing phenotype-genotype correlation in our interpretation strategy to criteria previously described, we identified 33 (25.2%) potentially pathogenic aberrations. 16 aberrations were confirmed pathogenic (16.4% syndromic, 8.5% non-syndromic patients); 9 were new and individual aberrations, 3 of them were pathogenic although inherited and one is as small as approx 200 kb. 13 of 16 further CNVs of unknown significance were classified likely benign, for 3 the significance remained unclear. High resolution array allows the detection of up to 12.2% of pathogenic aberrations in a diagnostic clinical setting. Although the majority of aberrations are larger, the detection of small causal aberrations may be relevant for family counseling. The number of remaining unclear CNVs is limited. Careful phenotype-genotype correlations of the individual CNVs and clinical features are challenging but remain a hallmark for CNV interpretation.

A neonate with the Pelger-Huët anomaly, cleft lip and palate, and agenesis of the corpus callosum, with a chromosomal microdeletion involving 1q41 to 1q42.12

We observed a neonate with cleft lip and palate, 13 sets of ribs, agenesis of the corpus callosum, slightly small penis, hypoglycemia, and what initially appeared to be a marked leukocyte 'left shift' on complete blood count, but which was actually a Pelger-Huët anomaly. A chromosomal microdeletion was identified at1q41-42.12.

A 54 Mb 11qter duplication and 0.9 Mb 1q44 deletion in a child with laryngomalacia and agenesis of corpus callosum

BACKGROUND

Partial Trisomy 11q syndrome (or Duplication 11q) has defined clinical features and is documented as a rare syndrome by National Organization of Rare Disorders (NORD). Deletion 1q44 (or Monosomy 1q44) is a well-defined syndrome, but there is controversy about the genes lying in 1q44 region, responsible for agenesis of the corpus callosum. We report a female child with the rare Partial Trisomy 11q syndrome and Deletion 1q44 syndrome. The genomic imbalance in the proband was used for molecular characterization of the critical genes in 1q44 region for agenesis of corpus callosum. Some genes in 11q14q25 may be responsible for laryngomalacia.

RESULTS

We report a female child with dysmorphic features, microcephaly, growth retardation, seizures, acyanotic heart disease, and hand and foot deformities. She had agenesis of corpus callosum, laryngomalacia, anterior ectopic anus, esophageal reflux and respiratory distress. Chromosome analysis revealed a derivative chromosome 1. Her karyotype was 46,XX,der(1)t(1;11)(q44;q14)pat. The mother had a normal karyotype and the karyotype of the father was 46,XY,t(1;11)(q44;q14). SNP array analysis showed that the proband had a 54 Mb duplication of 11q14q25 and a 0.9 Mb deletion of the submicroscopic subtelomeric 1q44 region. Fluorescence Insitu Hybridisation confirmed the duplication of 11qter and deletion of 1qter.

CONCLUSION

Laryngomalacia or obstruction of the upper airway is the outcome of increased dosage of some genes due to Partial Trisomy 11q Syndrome. In association with other phenotypic features, agenesis of corpus callosum appears to be a landmark phenotype for Deletion 1q44 syndrome, the critical genes lying proximal to SMYD3 in 1q44 region.

Genetic and functional analyses identify DISC1 as a novel callosal agenesis candidate gene

Agenesis of the corpus callosum (AgCC) is a congenital brain malformation that occurs in approximately 1:1,000-1:6,000 births. Several syndromes associated with AgCC have been traced to single gene mutations; however, the majority of AgCC causes remain unidentified. We investigated a mother and two children who all shared complete AgCC and a chromosomal deletion at 1q42. We fine mapped this deletion and show that it includes Disrupted-in-Schizophrenia 1 (DISC1), a gene implicated in schizophrenia and other psychiatric disorders. Furthermore, we report a de novo chromosomal deletion at 1q42.13 to q44, which includes DISC1, in another individual with AgCC. We resequenced DISC1 in a cohort of 144 well-characterized AgCC individuals and identified 20 sequence changes, of which 4 are rare potentially pathogenic variants. Two of these variants were undetected in 768 control chromosomes. One of these is a splice site mutation at the 5' boundary of exon 11 that dramatically reduces full-length mRNA expression of DISC1, but not of shorter forms. We investigated the developmental expression of mouse DISC1 and find that it is highly expressed in the embryonic corpus callosum at a critical time for callosal formation. Taken together our results suggest a significant role for DISC1 in corpus callosum development.

New cases and refinement of the critical region in the 1q41q42 microdeletion syndrome

Microdeletions of 1q41q42 have recently been classified as a syndrome. Features include significant developmental delay and characteristic dysmorphic features as well as cleft palate, clubfeet, seizures, and short stature in some individuals, with a clinical diagnosis of Fryns syndrome in two individuals with congenital diaphragmatic hernia at the severe end of the spectrum. The gene DISP1, which is involved in sonic hedgehog signaling, has been proposed as a candidate for the midline defects in this syndrome. We undertook a genotype-phenotype analysis of seven previously unreported individuals with deletions of 1q41q42 that range from 777 kb to 6.87 Mb. Three of the individuals in our cohort do not display the major features of the syndrome and have more proximal deletions that only overlap with the previously described 1q41q42 smallest region of overlap (SRO) at DISP1. One individual with several features of the syndrome has a more distal deletion that excludes DISP1. The three remaining individuals have larger deletions that include the entire SRO and demonstrate features of the microdeletion syndrome. Confounding genotype-phenotype correlations, one of the small deletions involving DISP1 was inherited from a phenotypically normal parent. DISP1 haploinsufficiency may not be solely responsible for the major features of 1q41q42 microdeletion syndrome, and other genes in the SRO likely play a role in the phenotype. Additionally, some features present in a minority of individuals, such as Pelger-Huët anomaly, may be attributed to deletions of genes outside of the SRO.