Mosaic variegated aneuploidy syndrome 2 (MVA2) is an uncommon autosomal recessive genetic condition caused by mutations in the CEP57 gene. It is characterized by intrauterine growth restriction, severe short stature, facial dysmorphism, and skeletal abnormalities. Most affected individuals also show congenital cardiac defects and delayed development. To date, only 16 patients have been reported. We report a 6-year-old girl of consanguineous Moroccan parents, presenting with severe short stature, clinodactyly, and dysmorphic facial features including prominent forehead, triangular face, micro-retrognathia, and low set ears. Neurodevelopment was initially normal, but mild intellectual disability was then noted. Genetic testing including karyotype, array-CGH, and Silver-Russell syndrome were normal. Finally, whole exome sequencing revealed a homozygous c.834_844dupCAATGTTCAGC variant in CEP57, classified as likely pathogenic. Familial segregation confirmed heterozygosity in both parents and siblings. This report describes a novel homozygous variant of CEP57, expanding the clinical and genetic spectrum of MVA2 syndrome. Although, karyotype should be firstly requested if MVA is suspected, whole exome sequencing is crucial. Growth hormone therapy shows limited response in this syndrome, and the association with cancer predisposition should be further studied.

To explore the genetic etiology of two fetuses with Mosaic variegated aneuploidy syndrome (MVA) in a pedigree. A 30-year-old pregnant woman, who presented at the Center for Medical Genetics and Prenatal Diagnosis of Shandong Maternal and Child Health Care Hospital on November 16, 2023, was enrolled. Clinical data of the pedigree were collected, and peripheral blood samples from the parents and amniotic fluid samples from the two fetuses were obtained for genomic DNA extraction. Whole exome sequencing (WES) was performed on both fetuses, followed by Sanger sequencing for familial validation and pathogenicity analysis of candidate variants. Chromosomal karyotyping of the parents was conducted to quantify the proportion of premature chromatid separation (PCS). This study was approved by the Medical Ethics Committee of Shandong Maternal and Child Health Care Hospital (Ethics No. 2024-034). Both fetuses exhibited structural brain anomalies and developmental delays during the second trimester. Amniocyte karyotyping revealed low-level mosaic aneuploidy involving multiple chromosomes, while chromosomal microarray analysis (CMA) showed no abnormalities. Pregnancy termination was performed for fetus 1. WES identified compound heterozygous variants in BUB1B, i.e., c.2363_2364del (p.S788Cfs*29) and ss804270619: G>A, in both fetuses. Sanger sequencing confirmed paternal inheritance of c.2363_2364del and maternal inheritance of ss804270619:G>A. According to the American College of Medical Genetics and Genomics (ACMG) and Clinical Genome Resource (ClinGen) Standards and Guidelines for the Interpretation of Sequence Variants, the c.2363_2364del variant was classified as likely pathogenic (PVS1 + PM2_Supporting). Parental karyotyping demonstrated PCS traits, with a higher proportion of abnormal metaphases in the father. The compound heterozygous variants c.2363_2364del (p.S788Cfs*29) and ss804270619: G>A in BUB1B may constitute the genetic etiology of the two MVA fetuses in this pedigree.

Congenital heart defects are structural anomalies present at birth that can affect the function of the heart. Aneuploidy is a significant risk factor for congenital heart defects. Mosaic variegated aneuploidy syndrome, caused by mutations in Bub1b (encoding BubR1, a mitotic checkpoint protein), leads to congenital heart defects such as septal defects. However, the molecular rationale for how Bub1b mutations promote congenital heart defects associated with mosaic variegated aneuploidy syndrome remains unresolved. To study morphological, structural, and cellular consequences of BubR1 deletion in the heart, we crossed mice carrying conditional alleles of Bub1b with Nkx2.5-cre mice. Single-cell RNA sequencing was carried out to determine differentially expressed genes and biological processes in various cell types present in the developing heart. Trajectory analysis was carried out to determine the differentiation trajectory of BubR1 knockout embryonic hearts. Finally, CellChat analysis provided details on the major signaling interactions that were either absent or hyperactive in the BubR1 knockout heart. Here, we show that cardiac-specific BubR1 deletion causes embryonic lethality due to developmental stalling after cardiac looping with defects in cardiac maturation including chamber wall thickness, septation, and trabeculation. Single-cell transcriptomic profiling further revealed that the differentiation trajectory of cardiomyocytes is severely impacted with suppression of critical cardiogenesis genes. Hyperactivation of Wnt signaling in BubR1 knockout hearts indicated a disturbed homeostasis in cellular pathways essential for proper tissue morphogenesis of the heart. Taken together, these findings reveal that BubR1 is a crucial regulator of cardiac development in vivo, which ensures the proper timing of heart morphogenesis.

Mosaic variegated aneuploidy (MVA) is an autosomal recessive disorder characterized by mosaic aneuploidies, predominantly trisomies, involving multiple different chromosomes and tissues. The proportion of aneuploid cells varies, and most patients present with intrauterine growth delay, microcephaly, and a broad spectrum of congenital abnormalities. We report a patient with a distinctive type of MVA discovered in bone marrow (BM) when she was 3-month-old due to neutropenia and hypocellular bone marrow. She was followed up for more than 20 years, and different trisomic cells were repeatedly discovered in different tissues, whereas her clinical picture has never been severe. The main sign remained intermittent neutropenia, not cyclic and often not too severe, occasionally with anemia and thrombocytopenia. Retromicrognathia was the only dysmorphic sign. Unlike other patients with MVA, the trisomies in all tissues involved almost invariably chromosomes 18 and 19. Therefore, the peculiarities of our patient were the clinical and the atypical cytogenetic pictures. Nevertheless, we looked for mutations in the seven causative genes of the known types of MVA, but the results were negative. Then, we analyzed the entire exome to find out other possible causing mutations, but also this attempt failed to discover a possible cause of this distinctive form of MVA.

Mosaic variegated aneuploidy (MVA) is a rare condition in which abnormal chromosome counts (that is, aneuploidies), affecting different chromosomes in each cell (making it variegated) are found only in a certain number of cells (making it mosaic). MVA is characterized by various developmental defects and, despite its rarity, presents a unique clinical scenario to understand the consequences of chromosomal instability and copy number variation in humans. Research from patients with MVA, genetically engineered mouse models and functional cellular studies have found the genetic causes to be mutations in components of the spindle-assembly checkpoint as well as in related proteins involved in centrosome dynamics during mitosis. MVA is accompanied by tumour susceptibility (depending on the genetic basis) as well as cellular and systemic stress, including chronic immune response and the associated clinical implications.