[Analysis and clinical application of preimplantation genetic testing for monogenic disorders in a case with Spinal muscular atrophy "2+0" genotype].

OBJECTIVE: To explore the clinical application of preimplantation genetic testing for monogenic disorders (PGT-M) in an unique case with Spinal muscular atrophy (SMA) type 2+0. METHODS: A special SMA family presented at the Third Affiliated Hospital of Guangzhou Medical University on October 19, 2020 was selected as the study subject. Multiple ligation-dependent probe amplification (MLPA) and molecular tagging linkage analysis were carried out to identify the SMN1 genotype of the couple and their fetus. Subsequently, next-generation sequencing (NGS), molecular tagging linkage analysis, and chromosomal microarray analysis were employed to determine the haplotypes and validate the result of PGT-M on the 11 embryos derived for the couple. RESULTS: The female partner was identified as a carrier of the rare SMN1[2+0] variant, and prenatal diagnosis confirmed the fetus to be affected by SMA. Ultimately, PGT-M has successfully selected four embryos free from the pathogenic SMN1 variants and X chromosome deletion. CONCLUSION: PGT-M can effectively prevent the transmission of rare genetic variants such as the SMA 2+0 subtype in the families. Above finding has provided guidance for genetic counseling and family planning for the couple.

Molecular Epidemiology and Hematologic Characterization of Thalassemia in Guangdong Province, Southern China.

Introduction: About 2% of the population in the world are carriers of the thalassemia gene. Thalassemia is highly prevalent in Southern China, and traditional clinical testing methods would cause missed diagnosis of partial static thalassemia. Here, we reviewed and summarized a set of simple and clinically feasible thalassemia detection protocols adopted by the Prenatal Diagnosis and Reproductive Center of our hospital. Methods: From January 1, 2015, to December 31, 2020, 31 512 peripheral blood samples and 3828 prenatal samples were collected in our study. All the peripheral blood samples were performed through thalassemia screening by routine blood tests and hemoglobin electrophoresis and gene detection. The prenatal diagnosis would be implemented for the fetus if the parents were carriers of the same type of thalassemia. Results: A total of 6137 (19.48%) cases were diagnosed as thalassemia, in which 4749 (15.07%) were α-thalassemia, 1196 (3.80%) were ß-thalassemia and 192 (0.61%) were co-inheritance of α- and ß-thalassemia. For prenatal samples, 3160 (82.55%) cases were diagnosed as thalassemia, in which 2021 (52.80%) were α-thalassemia, 997 (26.05%) were ß-thalassemia and 142 (3.71%) were co-inheritance of α- and ß-thalassemia. In addition, we also found five novel mutations, including NC_000016.9:g.223681-227492del3812; HBA1: c.301-31_301-24delCTCGGCCCinsG; HBA2: c.95+7C>T for α-thalassemia and HBB: c.263_276delCACTGAGTGAGCTG; HBB: c.315+143G>A for ß-thalassemia. Conclusion: The present study updates the epidemiological characteristics and mutation spectrum of thalassemia in Southern China and demonstrated five novel mutations. Our research provides a reference for clinical diagnosis and treatment, prenatal diagnosis, or reproductive genetic counseling for patients with thalassemia in Guangdong.

Application of Restriction Site-Associated DNA Sequencing (RAD-Seq) for Copy Number Variation and Triploidy Detection in Human.

At present, low-pass whole-genome sequencing (WGS) is frequently used in clinical research and in the screening of copy number variations (CNVs). However, there are still some challenges in the detection of triploids. Restriction site-associated DNA sequencing (RAD-Seq) technology is a reduced-representation genome sequencing technology developed based on next-generation sequencing. Here, we verified whether RAD-Seq could be employed to detect CNVs and triploids. In this study, genomic DNA of 11 samples was extracted employing a routine method and used to build libraries. Five cell lines of known karyotypes and 6 triploid abortion tissue samples were included for RAD-Seq testing. The triploid samples were confirmed by STR analysis and also tested by low-pass WGS. The accuracy and efficiency of detecting CNVs and triploids by RAD-Seq were then assessed, compared with low-pass WGS. In our results, RAD-Seq detected 11 out of 11 (100%) chromosomal abnormalities, including 4 deletions and 1 aneuploidy in the purchased cell lines and all triploid samples. By contrast, these triploids were missed by low-pass WGS. Furthermore, RAD-Seq showed a higher resolution and more accurate allele frequency in the detection of triploids than low-pass WGS. Our study shows that, compared with low-pass WGS, RAD-Seq has relatively higher accuracy in CNV detection at a similar cost and is capable of identifying triploids. Therefore, the application of this technique in medical genetics has a significant potential value.

Generation of induced pluripotent stem cell line GZHMCi006-A from amniotic fluid-derived cells with deletion 14q syndrome.

The deletions of the long arm of chromosome 14 involving the 14q24-q32 region have been identified as deletion 14q (del 14q) syndrome, but were rarely reported. The patients with del 14q syndrome are observed a peculiar facial appearance and neurological defects, but the molecular mechanisms were not clear. Here we generated a human iPSC line from the patient's amniotic fluid cells with 24 Mb deletion in 14q24.3q32.31 which will serve as useful tools for studying the mechanism of del 14q syndrome and the genes involved, which will provide useful basic theory of prenatal diagnosis.

Noninvasive prenatal testing for ß-thalassemia by targeted nanopore sequencing combined with relative haplotype dosage (RHDO): a feasibility study.

Noninvasive prenatal testing (NIPT) for single gene disorders remains challenging. One approach that allows for accurate detection of the slight increase of the maternally inherited allele is the relative haplotype dosage (RHDO) analysis, which requires the construction of parental haplotypes. Recently, the nanopore sequencing technologies have become available and may be an ideal tool for direct construction of haplotypes. Here, we explored the feasibility of combining nanopore sequencing with the RHDO analysis in NIPT of ß-thalassemia. Thirteen families at risk for ß-thalassemia were recruited. Targeted region of parental genomic DNA was amplified by long-range PCR of 10 kb and 20 kb amplicons. Parental haplotypes were constructed using nanopore sequencing and next generation sequencing data. Fetal inheritance of parental haplotypes was classified by the RHDO analysis using data from maternal plasma DNA sequencing. Haplotype phasing was achieved in 12 families using data from 10 kb library. While data from the 20 kb library gave a better performance that haplotype phasing was achieved in all 13 families. Fetal status was correctly classified in 12 out of 13 families. Thus, targeted nanopore sequencing combined with the RHDO analysis is feasible to NIPT for ß-thalassemia.

[Clinical value of MLPA in the prenatal gene diagnosis of Duchenne muscular dystrophy].

OBJECTIVE: To investigate the clinical value of multiplex ligation-dependent probe amplification (MLPA) in the prenatal gene diagnosis of high risk pregnant women from Duchenne muscular dystrophy (DMD) families. METHODS: The 155 high risk pregnant women from DMD families were recruited from 2005 to 2012 in 4 hospitals in Guangzhou, such as Southern Hospital of Southern Medical University and the Third Affiliated Hospital of Guangzhou Medical University. Among all the samples, 7 were chorionic villus samples taken from early-stage pregnancy and 148 were amniotic fluid samples from mid-stage pregnancy. After the maternal contamination was eliminated, the fetal DMD gene screening was carried out by using MLPA. The mutation rates in DMD exons were calculated in all the 155 families. RESULTS: (1) Among the 155 fetuses of the DMD high risk pregnant women, there were 72 male fetuses and 83 female fetuses. In the male fetuses, there were 27 sufferers (38%). In the female fetuses, there were 28 carriers (34%). And there were 100 normal fetuses. (2) Among the 27 DMD sufferers, 22 cases were DMD exon homozygous deletions (14.2%, 22/155) and 5 cases were DMD exon duplications (3.2%, 5/155). Among the 28 carriers, 25 cases were gene heterozygous deletions (16.1%, 25/155) and 3 cases were gene heterozygous duplications (1.9%, 3/155). In the 155 families, the DMD mutations mainly occurred in exons 45-52, and the exon 49 had the highest mutation rates of 22 times. (3) Among the 7 cases of prenatal gene diagnosis using chorionic villus samples, 2 fetuses had the identical DMD genotypes with their mothers and probands. One was a DMD sufferer and the other was a carrier. Termination or continuation of pregnancy was suggested based on the genotype of the fetus. CONCLUSIONS: MLPA provides an accurate method in the prenatal diagnosis of DMD. It could be used to distinguish DMD gene homozygous deletions from heterozygous deletions and duplications. Therefore, it is valuable for DMD prenatal diagnosis in high-risk women. Chorionic villus sampling can be applied to the early prenatal diagnosis for DMD disease.