Molecular diagnosis of tuberous sclerosis complex in fetuses and infants: an institutional case series.

OBJECTIVE: We describe the clinical and genetic characteristics of fetuses and infants diagnosed with tuberous sclerosis complex (TSC) in our centre, prenatally or neonatally, for a better understanding of the benefits of early screening. METHODS: In this retrospective study, we analysed the data on one fetus and nine infants with a definitive TSC diagnosis by genetic criteria (five patients carrying TSC1 variants and 5 patients carrying TSC2 variants). We explored the differences between phenotypes of patients carrying TSC1 and TSC2 pathogenic variants. RESULTS: The most common initial presenting features of TSC were cardiac rhabdomyomas (CRs) that were observed in nine out of ten patients. The most common postnatal features, besides CR, were presented with subependymal nodules-in five patients, and hypomelanotic macules-in four patients. In total, 10 variants causing TSC were detected in this study, including 5 novel variants. We demonstrated that patients with TSC2 variants had earlier onset and more severe clinical manifestations compared with patients carrying TSC1 variants. CONCLUSION: Early diagnosis of TSC improves genetic counselling and perinatal management.

Two Novel Mutations Associated With Ataxia-Telangiectasia Identified Using an Ion AmpliSeq Inherited Disease Panel.

Ataxia-telangiectasia (A-T), or Louis-Bar syndrome, is a rare neurodegenerative disorder associated with immunodeficiency. For families with at least one affected child, timely A-T genotyping during any subsequent pregnancy allows the parents to make an informed decision about whether to continue to term when the fetus is affected. Mutations in the ATM gene, which is 150 kb long, give rise to A-T; more than 600 pathogenic variants in ATM have been characterized since 1990 and new mutations continue to be discovered annually. Therefore, limiting genetic screening to previously known SNPs by PCR or hybridization with microarrays may not identify the specific pathogenic genotype in ATM for a given A-T family. However, recent developments in next-generation sequencing technology offer prompt high-throughput full-length sequencing of genomic fragments of interest. This allows the identification of the whole spectrum of mutations in a gene, including any novel ones. We report two A-T families with affected children and current pregnancies. Both families are consanguineous and originate from Caucasian regions of Russia and Azerbaijan. Before our study, no ATM mutations had been identified in the older children of these families. We used ion semiconductor sequencing and an Ion AmpliSeq™ Inherited Disease Panel to perform complete ATM gene sequencing in a single member of each family. Then we compared the experimentally determined genotype with the affected/normal phenotype distribution in the whole family to provide unambiguous evidence of pathogenic mutations responsible for A-T. A single novel SNP was allocated to each family. In the first case, we found a mononucleotide deletion, and in the second, a mononucleotide insertion. Both mutations lead to truncation of the ATM protein product. Identification of the pathogenic mutation in each family was performed in a timely fashion, allowing the fetuses to be tested and diagnosed. The parents chose to continue with both pregnancies as both fetuses had a healthy genotype and thus were not at risk of A-T.

In silico size selection is effective in reducing false positive NIPS cases of monosomy X that are due to maternal mosaic monosomy X.

OBJECTIVES: The aim of this study was to establish maternal contribution to false positive noninvasive prenatal DNA screening (NIPS) results and develop the method to distinguish maternal and fetal origin of high-risk monosomy X NIPS calls including mosaic maternal cases. METHOD: A total of 906 women carrying singleton pregnancies have been recruited. Maternal plasma DNA semiconductor massive parallel sequencing was performed to detect common aneuploidies. For the case of high monosomy X risk call, analysis method to distinguish fetal and maternal monosomy X has been additionally applied. RESULTS: According to NIPS results, 18 patients had a high risk of fetal monosomy X. In 11 (61%) cases, fetal aneuploidy was confirmed by karyotyping. Other 7 cases were false positives. In 3 out of 7 cases, additional analysis based on in silico size selection was allowed to assume maternal monosomy X. In these cases, fluorescence in situ hybridization analysis confirmed mosaic monosomy X in maternal blood cells. CONCLUSION: The prevalence of mosaic monosomy X karyotype is 0.3% (3/906)-10 times higher than published before. Additional in silico size-selection and data analysis increases PPV for monosomy X from 61% to 73% for studied population.