OBJECTIVE: To investigate the results of preimplantation genetic testing for monogenic diseases (PGT-M) in a Chinese pedigree affected with Primary carnitine deficiency (PCD). METHODS: A pedigree affected with PCD who visited Hainan Women and Children's Medical Center in April 2023 due to "SLC22A5 gene mutation found in offspring genetic testing and preparing for a second child" was selected as the study subject. Pathogenicity of the proband's variant sites was determined by referring to the Standards and Guidelines for the Interpretation of Sequence Variants established by the American College of Medical Genetics and Genomics (ACMG). Sanger sequencing was used to verify the variant sites of SLC22A5 gene in the proband and her parents, and the single nucleotide polymorphism (SNP) haplotype of the family was constructed by SNP microarray (SNP array) method to determine the carrier status of pathogenic genes. After fertilization via assisted reproductive technology, whole genome amplification (WGA) was performed on the biopsied trophoblastic cells. Sanger sequencing, next-generation sequencing (NGS), and SNP array techniques were then used to detect the variants in the SLC22A5 gene and chromosome copy number variation (CNV) in the embryos. Embryos without the variants were selected for transferring. After the successful pregnancy of the proband's mother, amniocentesis was not performed for prenatal diagnosis due to repeated vaginal bleeding. After delivery, neonatal peripheral blood sample was collected to verify the results of PGT-M, and follow-up was conducted. This study was reviewed and approved by the Medical Ethics Committee of Hainan Women and Children's Medical Center (Ethics No. HNWCMC-2022-178). RESULTS: In this study, the c.338G>A and c.760C>T variants in SLC22A5 gene were evaluated as pathogenic variants. Sanger sequencing results of this family showed that the c.338G>A and c.760C>T variants of the proband were inherited from his father and mother, respectively. Haplotypes of c.338G>A and c.760C>T variants of SLC22A5 gene were successfully constructed. PGT-M results showed that 2 of the 8 blastulas biopsied failed WGA, and the CNV detection results of the remaining 6 blastocysts were all euploid: 2 had no mutations in the SLC22A5 gene, 3 were single heterozygous carriers of paternal or maternal origin, and 1 was compound heterozygous carriers of paternal and maternal origin. Combined with the embryo morphology score, an intrauterine singleton pregnancy was achieved after the successful transfer of an optimal embryo with no CNV abnormalities and no paternal or maternal SLC22A5 gene mutations, resulting in the birth of a healthy female baby at 38⁺³ weeks of gestation. The results of peripheral blood chromosomal karyotyping analysis, CNV detection and SLC22A5 gene c.338G>A and c.760C>T site variant detection of the infant were consistent with those of PGT-M, and no abnormality was found. CONCLUSION PGT-M had helped the couple carrying SLC22A5 gene variant to have a healthy offspring and effectively blocked the transmission of PCD in this family.
Adult ; Female ; Humans ; Male ; Pregnancy ; Cardiomyopathies ; China ; East Asian People/genetics* ; Genetic Testing/methods* ; High-Throughput Nucleotide Sequencing ; Hyperammonemia/genetics* ; Mutation ; Pedigree ; Polymorphism, Single Nucleotide ; Preimplantation Diagnosis/methods* ; Solute Carrier Family 22 Member 5/genetics* ; Carnitine/deficiency* ; Muscular Diseases

Abstract: Objective　To evaluate the free thalassaemia screening programme for preconception and pregnancy in Hainan Province, and to provide a theoretical basis for optimizing the screening process for thalassaemia. Methods From November 2020 to July 2021, a survey was conducted on 10 396 adults with Hainan household registration who participated in the Epidemiological Survey of Thalassemia in Hainan Residents in 19 cities and counties of Hainan Province. All of them underwent routine blood tests, haemoglobin electrophoresis tests and genetic tests for thalassaemia. The optimal diagnostic cut-off values for mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), and haemoglobin adult type 2 (HbA2) were determined using screening test indexes such as receiver operating characteristic curve and sensitivity. The diagnostic effectiveness of different primary screening programs for thalassemia gene carriers was evaluated. Results Using the existing MCV single-indicator thalassemia primary screening protocol in Hainan Province, where individuals with MCV<82 fL undergo thalassemia gene testing, resulted in a high missed diagnosis rate (34.06%) and low sensitivity (65.94%). The optimal cut-off values for MCV screening for alpha-and beta-thalassaemia were 84.45 fL and 79.05 fL, respectively; the optimal cut-off values for MCH screening for alpha-and beta-thalassaemia were 27.95 pg and 25.15 pg, respectively. The optimal cut-off value for HbA2 screening for alpha-thalassaemia was less than 2.55% and greater than 3.35% for beta-thalassaemia. The "combined HbA2 or MCH or MCV screening protocol" with the cut-off values recommended in this study had a better performance in primary screening for thalassemia, with the highest sensitivity (92.96%) and negative predictive value (92.67%) and the lowest underdiagnosis rate (7.04%), statistically significant differences compared with the existing protocol (P<0.05). Conclusions The current process of screening for thalassemia in Hainan Province may lead to missed diagnoses. The combined use of MCV, MCH and HbA2 for thalassemia screening, adopting locally suitable cutoff values for primary screening indicators, can improve the incidence of missed reporting of thalassemia and enhance diagnostic effectiveness.