Discordant phenotypes in monozygotic twins with 16p11.2 microdeletions including the SH2B1 gene

Molecular cytogenetic characterization of 16p11.2 microdeletions with diverse prenatal phenotypes: Four cases report and literature review

OBJECTIVE

Chromosome 16p11.2 deletions have been recognized as a genetic disorder with well-described postnatal phenotypes. However, the prenatal manifestations are atypical for lacking of enough evidence.

CASE REPORT

Four pregnant women underwent amniocentesis for cytogenetic analysis and chromosomal microarray analysis (CMA) because of various indications for prenatal diagnosis: prenatal ultrasound abnormalities (cases 1, 2 and 4) and the childbearing history of cerebral palsy child (case 3). No overlapping phenotypes were observed in cases 1, 2 and 4, which might indicate phenotypic diversities in prenatal phenotypes for 16p11.2 microdeletion. All four fetuses showed normal karyotypic results while CMA identified 0.303-0.916 Mb microdeletions of 16p11.2, encompassing BP2-BP3 and BP4-BP5 regions separately. According to the parental CMA verification, case 1 carried a maternal inherited duplication in the region of Xp22.33 and a de novo deletion in the region of Xp21.1. All parents opted for the termination of pregnancies based upon genetic counselling.

CONCLUSION

Our findings enriched the intrauterine phenotypic features of 16p11.2 microdeletions, which would be beneficial for genetic counselling in clinic. In addition, preimplantation genetic testing was recognized as a first-tier approach for such carriers if they intended to conceive again.

Microduplication of 16p11.2 locus potentiates hypertrophic obesity in association with imbalanced triglyceride metabolism in white adipose tissue

Scope

Copy number variation (CNV) of 16p11.2 is a common genetic factor contributing to the etiology of abnormal weight status, while the underlying mechanism is not fully elucidated yet.

Methods and Results

The 16p11.2 CNV mouse model with microduplication of the 7Slx1b‐Sept1 region (dp/+) is evaluated under normal chow conditions. Compared to the wild type littermates (WT), the dp/+ mice exhibit obvious obese phenotype characterized by significant increase in body mass index, fat pad mass, and fat ratio, with visceral‐dominant fat deposits at 12‐week age. White adipose tissue (WAT), liver tissue, and plasma are sampled to assess the comorbid metabolic syndrome. In dp/+ mice, histopathologic analyses reveal hypertrophic adipocytes and hepatic steatosis; serological examinations show hyperlipemia and hyperinsulinemia. Further, by comparing lipidomic and transcriptomic profiling of epididymal WAT between dp/+ and WT mice, the study finds the triglyceride (TG) accumulation in dp/+ mice in association with the dysfunction of lipid droplets. Validation of TG‐metabolism‐associated genes in WAT and in primary cultured adipocytes show enhanced TG synthesis and declined TG hydrolysis in the dp/+ model.

Conclusion

This study elucidates that the imbalanced TG synthesis/hydrolysis in adipocytic lipid droplets may contribute to the hypertrophic obesity and metabolic disorders in mice with 16p11.2 microduplication.

Overlap phenotypes of the left ventricular noncompaction and hypertrophic cardiomyopathy with complex arrhythmias and heart failure induced by the novel truncated DSC2 mutation

Background

The left ventricular noncompaction cardiomyopathy (LVNC) is a rare subtype of cardiomyopathy associated with a high risk of heart failure (HF), thromboembolism, arrhythmia, and sudden cardiac death.

Methods

The proband with overlap phenotypes of LVNC and hypertrophic cardiomyopathy (HCM) complicates atrial fibrillation (AF), ventricular tachycardia (VT), and HF due to the diffuse myocardial lesion, which were diagnosed by electrocardiogram, echocardiogram and cardiac magnetic resonance imaging. Peripheral blood was collected from the proband and his relatives. DNA was extracted from the peripheral blood of proband for high-throughput target capture sequencing. The Sanger sequence verified the variants. The protein was extracted from the skin of the proband and healthy volunteer. The expression difference of desmocollin2 was detected by Western blot.

Results

The novel heterozygous truncated mutation (p.K47Rfs*2) of the DSC2 gene encoding an important component of desmosomes was detected by targeted capture sequencing. The western blots showed that the expressing level of functional desmocollin2 protein (~ 94kd) was lower in the proband than that in the healthy volunteer, indicating that DSC2 p.K47Rfs*2 obviously reduced the functional desmocollin2 protein expression in the proband.

Conclusion

The heterozygous DSC2 p.K47Rfs*2 remarkably and abnormally reduced the functional desmocollin2 expression, which may potentially induce the overlap phenotypes of LVNC and HCM, complicating AF, VT, and HF.

Clinical and molecular characterization of craniofrontonasal syndrome: new symptoms and novel pathogenic variants in the EFNB1 gene

Background

Craniofrontonasal syndrome (CFNS) is a rare X-linked disorder that results from pathogenic variants in the EFNB1 gene. The syndrome paradoxically presents with greater severity of the symptoms in heterozygous females than hemizygous males.

Results

We have recruited and screened a female cohort affected with CFNS. Our primary finding was the description of monozygotic twins, i.e., patients 5 and 6, discordant for the CFNS phenotype. Intriguingly, patient 5 presented classical CFNS gestalt, whereas patient 6 manifested only very subtle craniofacial features, not resembling CFNS. Besides, we have expanded the mutational spectrum of the EFNB1 gene through reporting four novel pathogenic variants—p.(Trp12*), p.(Cys64Phe), p.(Tyr73Metfs*86), p.(Glu210*). All those alterations were found applying either targeted NGS of a custom gene panel or PCR followed by Sanger sequencing and evaluated using in silico predictors. Lastly, we have also expanded the CFNS phenotypic spectrum by describing in patient 3 several novel features of the syndrome, such as bifid hallux, bicornuate uterus, and abnormal right ovary segmented into six parts.

Conclusions

We have described the unreported so far differences of the clinical phenotype in the monozygotic twin patients 5 and 6 harboring an identical p.(Glu210*) variant located in the EFNB1 gene. With our finding, we have pointed to an unusual phenomenon of mildly affected females with CFNS, who may not manifest features suggestive of the syndrome. Consequently, this study may be valuable for geneticists consulting patients with craniofacial disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01914-1.

Clinical Utility and the Yield of Single Nucleotide Polymorphism Array in Prenatal Diagnosis of Fetal Central Nervous System Abnormalities

Applying single nucleotide polymorphism (SNP) array to identify the etiology of fetal central nervous system (CNS) abnormality, and exploring its association with chromosomal abnormalities, copy number variations, and obstetrical outcome. 535 fetuses with CNS abnormalities were analyzed using karyotype analysis and SNP array. Among the 535 fetuses with CNS abnormalities, chromosomal abnormalities were detected in 36 (6.7%) of the fetuses, which were consistent with karyotype analysis. Further, additional 41 fetuses with abnormal copy number variations (CNVs) were detected using SNP array (the detection rate of additional abnormal CNVs was 7.7%). The rate of chromosomal abnormalities, but not that of pathogenic CNVs in CNS abnormalities with other ultrasound abnormalities was significantly higher than that in isolated CNS abnormalities. The rates of chromosomal abnormalities and pathogenic CNVs in fetuses with spine malformation (50%), encephalocele (50%), subependymal cyst (20%), and microcephaly (16.7%) were higher than those with other isolated CNS abnormalities. The pregnancies for 36 cases with chromosomal abnormalities, 18 cases with pathogenic CNVs, and three cases with VUS CNVs were terminated. SNP array should be used in the prenatal diagnosis of fetuses with CNS abnormalities, which can enable better prenatal assessment and genetic counseling, and affect obstetrical outcomes.

Discordance of cardiovascular abnormalities in a monozygotic twin pair carrying a class II 1q21.1 microdeletion

OBJECTIVE

We present the prenatal diagnosis of a class II 1q21.1 microdeletion in monozygotic (MZ) twins with discordant phenotypes.

CASE REPORT

A monochorionic diamniotic twin pair presented with discordant ultrasound anomalies; twin A had cardiovascular abnormalities, while twin B did not. No specific complications were noted in the twins during pregnancy. A single nucleotide polymorphism array revealed an identical class II 1q21.1 microdeletion inherited from a phenotypically normal mother and identified the twins as MZ. The deleted region encompassed both the proximal 1q21.1 thrombocytopenia absent radius syndrome region and the distal 1q21.1 recurrent microdeletion region. No other rare copy number variants (CNVs) were identified, and concordance was observed in the CNVs between the twins.

CONCLUSION

Discordant cardiovascular abnormalities may occur in MZ twins carrying the same class II 1q21.1 microdeletion. Further studies involving discordant MZ twins are needed to determine the modifying factors of the phenotypic heterogeneity of the microdeletion.

Deletion at 12q12 increases the risk of developmental delay and intellectual disability

Single-nucleotide polymorphism (SNP) arrays have been widely used to identify novel genomic imbalances. Many of these genomic imbalances have been confirmed to interact with developmental delays, intellectual disabilities (IDs), and congenital defects. Here, we identify a Chinese girl with a 3.18-Mb deletion at 12q12 (human genome build 19: 43,418,911-46,601,627) who showed postnatal growth delay, low-set ears, small hands and feet, widely spaced nipples, and blue sclerae. Deletions at 12q12 are extremely rare chromosomal imbalances; only four cases involving a deletion of this type have previously been reported. In these five sporadic cases, all of the patients exhibited developmental issues accompanied by different degrees of ID. A review of DECIPHER patient data revealed an additional six cases involving genomic deletion at 12q12. Many of the patients in these cases exhibited developmental delay and ID. When these patients were included, 91% and 73% of individuals with a deletion in this chromosomal region presented with developmental retardation and ID, respectively. Database searches indicated that this copy number variant (CNV) has not been found in normal humans. Therefore, we suggest that a CNV in this region is a risk factor for developmental retardation and ID.