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Human growth has an estimated heritability of about 80%-90%. Nevertheless, the underlying cause of shortness of stature remains unknown in the majority of individuals. Genome-wide association studies (GWAS) showed that both common single nucleotide polymorphisms and copy number variants (CNVs) contribute to height variation under a polygenic model, although explaining only a small fraction of overall genetic variability in the general population. Under the hypothesis that severe forms of growth retardation might also be caused by major gene effects, we searched for rare CNVs in 200 families, 92 sporadic and 108 familial, with idiopathic short stature compared to 820 control individuals. Although similar in number, patients had overall significantly larger CNVs \((p-value <1 x 10^{-7})\). In a gene-based analysis of all non-polymorphic CNVs >50 kb for gene function, tissue expression, and murine knock-out phenotypes, we identified 10 duplications and 10 deletions ranging in size from 109 kb to 14 Mb, of which 7 were de novo (p < 0.03) and 13 inherited from the likewise affected parent but absent in controls. Patients with these likely disease causing 20 CNVs were smaller than the remaining group (p < 0.01). Eleven (55%) of these CNVs either overlapped with known microaberration syndromes associated with short stature or contained GWAS loci for height. Haploinsufficiency (HI) score and further expression profiling suggested dosage sensitivity of major growth-related genes at these loci. Overall 10% of patients carried a disease-causing CNV indicating that, like in neurodevelopmental disorders, rare CNVs are a frequent cause of severe growth retardation.
Fanconi anemia (FA) is a rare bone marrow failure and cancer predisposition syndrome resulting from pathogenic mutations in genes encoding proteins participating in the repair of DNA interstrand crosslinks (ICLs). Mutations in 17 genes (FANCA-FANCS) have been identified in FA patients, defining 17 complementation groups. Here, we describe an individual presenting with typical FA features who is deficient for the ubiquitin-conjugating enzyme (E2), UBE2T. UBE2T is known to interact with FANCL, the E3 ubiquitin-ligase component of the multiprotein FA core complex, and is necessary for the monoubiquitination of FANCD2 and FANCI. Proband fibroblasts do not display FANCD2 and FANCI monoubiquitination, do not form FANCD2 foci following treatment with mitomycin C, and are hypersensitive to crosslinking agents. These cellular defects are complemented by expression of wild-type UBE2T, demonstrating that deficiency of the protein UBE2T can lead to Fanconi anemia. UBE2T gene gains an alias of FANCT.
Arrhythmogenic cardiomyopathy (ACM) is characterized by fibro-fatty replacement of the myocardium, heart failure and life-threatening ventricular arrhythmias. Causal mutations were identified in genes encoding for proteins of the desmosomes, predominantly plakophilin-2 (PKP2) and desmoglein-2 (DSG2). We generated gene-edited knock-out iPSC lines for PKP2 (JMUi001-A-2) and DSG2 (JMUi001-A-3) using the CRISPR/Cas9 system in a healthy control iPSC background (JMUi001A). Stem cell-like morphology, robust expression of pluripotency markers, embryoid body formation and normal karyotypes confirmed the generation of high quality iPSCs to provide a novel isogenic human in vitro model system mimicking ACM when differentiated into cardiomyocytes.
Background: Genes that, when mutated, cause Fanconi anemia or greatly increase breast cancer risk encode for proteins that converge on a homology-directed DNA damage repair process. Mutations in the SLX4 gene, which encodes for a scaffold protein involved in the repair of interstrand cross-links, have recently been identified in unclassified Fanconi anemia patients. A mutation analysis of SLX4 in German or Byelorussian familial cases of breast cancer without detected mutations in BRCA1 or BRCA2 has been completed, with globally negative results.
Methods: The genomic region of SLX4, comprising all exons and exon-intron boundaries, was sequenced in 94 Spanish familial breast cancer cases that match a criterion indicating the potential presence of a highly-penetrant germline mutation, following exclusion of BRCA1 or BRCA2 mutations.
Results: This mutational analysis revealed extensive genetic variation of SLX4, with 21 novel single nucleotide variants; however, none could be linked to a clear alteration of the protein function. Nonetheless, genotyping 10 variants (nine novel, all missense amino acid changes) in a set of controls (138 women and 146 men) did not detect seven of them. Conclusions: Overall, while the results of this study do not identify clearly pathogenic mutations of SLX4 contributing to breast cancer risk, further genetic analysis, combined with functional assays of the identified rare variants, may be warranted to conclusively assess the potential link with the disease.