A Fetus with Maternal Uniparental Disomy on Chromosome 20: Case Report with Genetic Analysis and Prenatal Diagnosis.

BACKGROUND: A fetus with increased copy number of chromosome 20 was identified by NIPT. Here we utilize several genetic tests and analyses to illuminate the etiology of such aneuploidy. METHODS: Amniotic fluid cells were extracted from pregnant woman and sent for karyotype and chromosomal microarray analysis (CMA). Trio pedigree analysis was conducted with Chromosome Analysis Suite and uniparental disomy (UPD)-tool software. RESULTS: CMA identified consistent results, which were 2 regions of homozygosity: arr[GRCh37]20p12.2q11.1 (11265096_26266313)hmz and arr[GRCh37]20q11.21q13.2(29510306_54430467)hmz. The trio pedigree analysis discovered that the fetal chromosome 20 was the entire maternal UPD mosaic with isodisomy and heterodisomy. CONCLUSIONS: When a large segment of chromosome is homozygous, appropriate genetic tests are required to find the potential mechanisms for UPD formation.

Evaluating the relationship between Clinical G6PD enzyme activity and gene variants.

Glucose-6-phosphate dehydrogenase (G6PD) is a the first and rate-limiting enzyme that plays a critical role in G6PD deficiency, the most common enzyme disorder worldwide, is related to intravascular hemolysis. To determine the clinical enzyme activity level in different G6PD variants, we evaluated 15 variant from 424 clinical blood samples by using multicolor melting curve analysis and DNA sequencing. The results showed that the enzyme activities of the hemizygous deficient were 1.5-2.4 U/gHb, which was significantly lower than those of the heterozygous (P < 0.001) and the compound heterozygous variants (P < 0.05). Since the hemizygous of c.1024C > T (Chinese-5) mutation affects the kinetic parameters of G6PD and increase utilization of analogues, its enzyme activity is more than those of other mutations that mutated in the ß+α region of G6PD. The heterozygous enzyme levels ranged from 6.5-20.1 U/gHb; and there was no significant difference among different heterozygous variants (P > 0.05). The enzyme activity levels of the compound heterozygous mutation were mainly in the range of 1.7-3.8 U/gHb, which was much lower than that of the heterozygous mutation (P < 0.001). In summary, our findings revealed that the enzyme activity of G6PD in blood have a significant relationship with genotype of G6PD.

Evaluation of the Diagnostic Accuracy of the CareStart™ Glucose-6-Phosphate Dehydrogenase Deficiency Rapid Diagnostic Test among Chinese Newborns.

Previous studies have shown that the CareStart™ G6PD Deficiency rapid diagnostic test has high diagnostic accuracy on G6PD deficiency in Africa and Thailand, but not in China. As there are regional differences of G6PD genotype distribution, we are attending to verify the effectiveness of the kit in Chinese population. The study cohort included 247 newborns admitted to our hospital for jaundice. The quantitative detection of G6PD enzyme activity and G6PD gene mutations analysis was used to classify the status of G6PD deficiency. The performance of CareStart™ assays was verified by calculating the sensitivity, specificity and area under the receiver operating characteristic curve (AUC) based on the corrected G6PD deficiency status. In male newborns, the sensitivity of the CareStart™ assay was 98.9%, the specificity was 94.2% and the AUC was 0.97. In female newborns, the sensitivity was 58.5% when the cutoff value of residual enzyme activity was 100%; however, the sensitivity was 100% when the cutoff value was 60%. Therefore, the CareStart™ test can effectively screen G6PD deficiency in male newborns and female infants with less than 60% residual enzyme activity, female infants with residual enzyme activities of 60-100% are more likely to be missed diagnosed among Chinese newborns.

Rare double heterozygosity for poly A(A〉 G) and CD17(A〉 T) of beta thalassemia intermedia in a Chinese family.

Beta thalassemia is a hereditary disorder resulted from mutations in the ß globin gene leading to alpha/beta imbalance, ineffective erythropoiesis, and chronic anemia. Three types have been defined, based on the degree of reduced beta-globin chain synthesis and clinical phenotype: major, intermedia and minor (heterozygote carrier state). Beta thalassemia intermedia is characterized by heterogeneity for the wide clinical spectrum of various genotypes and a wide range of presentations. The genotypes of beta thalassemia intermedia are much complicated referring to ß+/ß+,ß+/ß0, Hb E/ß0, ß0/ß0 compounding alpha thalassemia and so on. In this present case, we reported a rare beta thalassemia intermedia genotype of double heterozygosity for poly A (A〉 G) and CD17(A〉 T) indicated of ß+/ß0 in a Chinese family.

[Genetic analysis of a fetus with partial 18p tetraploidy syndrome].

OBJECTIVE: To analyze a fetus with abnormal cardiac ultrasound by using various techniques and explore its genotype-phenotype correlation. METHODS: Lymphocytes derived from umbilical cord blood sample were subjected to G-banding analysis. Short tandem repeats quantitative fluorescence PCR (STR-QF-PCR) was used for analysis of fetal DNA as an auxiliary test. Low-coverage whole genome sequencing (WGS) was used to detect chromosomal deletion/duplication which exceeded 100 kb in size. RESULTS: The karyotype of the fetus was 47,XN,+mar. As detected by STR-QF-PCR, the copy number of GATA178F11 locus on chromosome 18 was 4, and the duplicated fragment was derived from the mother. WGS suggested that the fetus to be 46,XN,dup(18p11.21p11.32).seq [GRCh37/hg19](10 001-15 378 887)× 4, with the duplicated fragment spanning approximately 15.38 Mb. CONCLUSION: The cardiac malformation of the fetus may be attributed to the partial duplication of chromosome 18p. Combined cytogenetic and molecular methods can facilitate prenatal detection of genetic abnormalities.

Rapid detection of G6PD mutations by multicolor melting curve analysis.

The MeltPro G6PD assay is the first commercial genetic test for glucose-6-phosphate dehydrogenase (G6PD) deficiency. This multicolor melting curve analysis-based real-time PCR assay is designed to genotype 16 G6PD mutations prevalent in the Chinese population. We comprehensively evaluated both the analytical and clinical performances of this assay. All 16 mutations were accurately genotyped, and the standard deviation of the measured Tm was <0.3°C. The limit of detection was 1.0ng/µL human genomic DNA. The assay could be run on four mainstream models of real-time PCR machines. The shortest running time (150min) was obtained with LightCycler 480 II. A clinical study using 763 samples collected from three hospitals indicated that, of 433 samples with reduced G6PD activity, the MeltPro assay identified 423 samples as mutant, yielding a clinical sensitivity of 97.7% (423/433). Of the 117 male samples with normal G6PD activity, the MeltPro assay confirmed that 116 samples were wild type, yielding a clinical specificity of 99.1% (116/117). Moreover, the MeltPro assay demonstrated 100% concordance with DNA sequencing for all targeted mutations. We concluded that the MeltPro G6PD assay is useful as a diagnostic or screening tool for G6PD deficiency in clinical settings.

DNA hypermethylation and X chromosome inactivation are major determinants of phenotypic variation in women heterozygous for G6PD mutations.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked incompletely dominant enzyme deficiency that results from G6PD gene mutations. Women heterozygous for G6PD mutations exhibit variation in the loss of enzyme activity but the cause of this phenotypic variation is unclear. We determined DNA methylation and X-inactivation patterns in 71 G6PD-deficient female heterozygotes and 68 G6PD non-deficient controls with the same missense mutations (G6PD Canton c.1376G>T or Kaiping c.1388G>A) to correlate determinants with variable phenotypes. Specific CpG methylations within the G6PD promoter were significantly higher in G6PD-deficient heterozygotes than in controls. Preferential X-inactivation of the G6PD wild-type allele was determined in heterozygotes. The incidence of preferential X-inactivation was 86.2% in the deficient heterozygote group and 31.7% in the non-deficient heterozygote group. A significant negative correlation was observed between X-inactivation ratios of the wild-type allele and G6PD/6-phosphogluconate dehydrogenase (6PGD) ratios in heterozygous G6PD Canton (r=-0.657, p<0.001) or Kaiping (r=-0.668, p<0.001). Multivariate logistic regression indicated that heterozygotes with hypermethylation of specific CpG sites in the G6PD promoter and preferential X-inactivation of the wild-type allele were at risk of enzyme deficiency.

[Identification of a novel frameshift mutation of human androgen receptor gene in a patient featuring complete androgen insensitivity syndrome].

OBJECTIVE: To identify potential mutation of human androgen receptor (AR) gene in a patient with complete androgen insensitivity syndrome (CAIS). METHODS: DNA sequences of 8 exons and exon/intron boundaries of the AR gene were amplified with PCR and directly sequenced. RESULTS: DNA sequencing has revealed a frameshift mutation due to deletion of nucleotide C at position 3507 in exon 6, which gave rise to a stop codon resulting premature termination for translation. CONCLUSION: A novel frameshift mutation in exon 6 of AR gene probably underlies the disease in our patient.

[Large-scale population-based genetic screening and prenatal diagnosis for thalassemias in Zhuhai City of Guangdong Province].

OBJECTIVE: To report the results of preventive control program of severe thalassemias in Zhuhai City of Guangdong Province from 1998 to 2010. METHODS: As the guide centre of marriage and childbearing and the greatest maternity hospital in Zhuhai City of Guangdong Province, Zhuhai Municipal Maternity and Child Healthcare Hospital constructed the genetic screening network for thalassemias testing and referred for follow-up and for genetic counseling. The couples for premarital medical examination or regular healthcare examination in pregnancy were enrolled to this preventive control program. A conventional strategy of screening for heterozygote was used to identify the α- and ß-thalassemia traits in women and their spouses according to the standard procedures of hematological phenotype analysis which was recommended by Thalassemia International Federation (TIF). Then those suspected couples at risk were diagnosed for α- and ß-thalassemia by PCR-based DNA assays. The couples at risk for severe thalassemias were counseled and offered prenatal diagnosis and termination of pregnancy in case of an affected fetus in the rights of consent and of option voluntarily. RESULTS: From January 1998 to December 2010, 85 522 brides and grooms-to-be for premarital screening and 41 503 pregnant women in addition to 14 141 partners for prenatal screening were recorded, the covering rates of premarital screening and prenatal screening in the city were 92.698% (from 1998 to 2003) and 27.667% (from 2004 to 2010), respectively. Totally 10 726 cases were found to be the carriers of thalassemias, with 7393 for α-thalassemia (5.237%, 7 393/141 166) and 3333 for ß-thalassemia (2.361%, 3 333/141 166). A total of 257 couples at-risk for severe thalassemias were detected including 190 for α-thalassemia and 67 for ß-thalassemia. Among them, 251 (97.7%, 251/257) couples were performed prenatal diagnosis. During the preventive control program, a total of 72 fetuses with severe thalassemias including hemoglobin H disease were voluntarily terminated. In Zhuhai City, the average annual birth rate of fetuses with severe thalassemia was declined by 32.9% (49/149). CONCLUSIONS: This study has reduced effectively birth rate of perinatal infants with severe thalassemias in Zhuhai City by genetic screening and prenatal diagnosis of thalassemia in the large population of 13 years. Our summary comes out of technical proposals for prenatal screening and diagnosis, which could be take example by preventative control of thalassemia in other regions of China where are prevalent.

Rapid, accurate detection of TMPRSS6 gene causative mutations with a high-resolution melting assay.

Mutations of the TMPRSS6 gene are considered the major genetic factors for iron-refractory iron deficiency anemia (IRIDA). Artificial clone libraries containing 17 known mutations of the TMPRSS6 gene were used to develop a high-resolution melting (HRM) assay for the detection of 17 TMPRSS6 gene mutations. The melting temperatures and melting curves were able to distinguish the different genotypes of the 17 TMPRSS6 gene mutations. We used replicate experiments to evaluate the reproducibility of the assay, and the coefficients of variation were in the range 0.0091% to 0.0873%. A total of 145 Chinese patients with IDA were screened with this assay and no TMPRSS6 gene causative mutation was found in any patient. The HRM assay was proved to be rapid, accurate and cost-effective method to identify the TMPRSS6 gene mutations and can be used in the clinical diagnosis of IRIDA.

A melting curve analysis--based PCR assay for one-step genotyping of ß-thalassemia mutations a multicenter validation.

The increasing number of disease-causing mutations demands a simple, direct, and cost-effective diagnostic genotyping technique capable of detecting multiple mutations. This study validated the efficacy of a novel melting curve analysis-based genotyping assay (MeltPro HBB assay) for 24 ß-thalassemia mutations in the Chinese population. The diagnostic potential of this assay was evaluated in 1022 pretyped genomic DNA samples, including 909 clinical cases of ß-thalassemia minor or major, using a double-blind analysis in a multicenter validation study. Reproducibility of the assay was 100%, and the limit of detection was 10 pg per reaction. All 24 ß-thalassemia mutations were accurately genotyped, and ß-thalassemia genotypes were correctly determined in all 1022 samples, yielding overall sensitivity and specificity of 100%. The concordance rate was 99.4% between this assay and the reference method. It was concluded that the MeltPro HBB assay is useful for reliable genotyping of multiple ß-thalassemia mutations in clinical settings and may have potential as a versatile method for rapid genotyping of known mutations because of its high throughput, accuracy, ease of use, and low cost.

[A community-based genetic screening of large-scale population and prenatal diagnosis for alpha and beta thalassemia in Zhuhai city of Guangdong province].

OBJECTIVE: To describe a community-based model for prevention and control of severe alpha and beta thalassemias in Zhuhai city of Guangdong province. METHODS: Couples for premarital medical examination or regular healthcare examination in pregnancy were enrolled in this prospective screening program, which was supported by the two-level network composed of 6 local hospitals for testing thalassemias and follow-up for genetic counseling. A conventional heterozygote screening strategy was used to determine alpha and beta thalassemia traits in women and their partners according to the standard procedures of hematological phenotype analysis. Then confirmative diagnosis of alpha and beta thalassemia was performed on those couples suspected at-risk for severe thalassemia by using the PCR-based molecular diagnostic assays. The couples at-risk for severe thalassemia were counseled and offered prenatal diagnosis and termination of pregnancy in case of an affected fetus. RESULTS: During the period between January 1998 and December 2005, the screened records included 85522 young females and their partners for premarital screening and 10439 pregnant women for prenatal screening, with 71.38% coverage of total population recorded in this city for premarital screening. Six thousands five hundreds and sixty-three individuals in total were found to be the carriers of thalassemias, with 4312 for alpha thalassemia (4.5%) and 2251 for beta thalassemia (2.3%), respectively. One hundred and forty-eight couples were diagnosed to be at-risk for thalassemias, including 103 for alpha thalassemia and 45 for beta thalassemia, respectively. Successful prenatal diagnosis was made for 142 (98 for alpha thalassemia and 44 for beta thalassemia) out of 148 (95.9%) pregnancies at-risk for severe thalassemias. Twenty-three cases of hydrops fetalis, 4 of Hb H diseases and 14 of beta thalassemia were identified. All 41 pregnancies with affected fetuses were voluntarily terminated. Thus, this has led to a marked decrease of severe thalassemia syndrome since the program started. CONCLUSION: We presented the first community-based prospective screening program in China for control of alpha and beta thalassemia in Zhuhai city with a population of 1.29 million through premarital or prenatal screening. This model could be used for control of thalassemias and other hemoglobinopathies in other regions of China and also in other developing countries.

[Rapid differential diagnosis of thalassemia trait and iron-deficiency anemia with stepwise regression analysis].

OBJECTIVE: To establish a method for rapid differential diagnosis of thalassemia trait (TT) and iron-deficiency anemia (IDA) using stepwise regression analysis. METHODS: Stepwise regression equation was established for differential diagnosis of TT and IDA according to the red cell index, and the accuracy of the differential diagnosis was evaluated using blind analysis. RESULTS: The accuracy of this equation for differential diagnosis of TT and IDA was 86.82%. The sensitivity, specificity and Youden's index in prediction of TT and IDA were 94.29%, 79.66%, 73.9 and 76.92%, 90.52%, and 67.4%, respectively. CONCLUSION: The stepwise regression equation using the red cell index is concise, rapid, and sensitive in differential diagnosis of TT and IDA, and can be well applicable in clinical practice.

Development and evaluation of a reverse dot blot assay for the simultaneous detection of six common Chinese G6PD mutations and one polymorphism.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common inherited disorder worldwide including southern China. We developed and validated a reverse dot blot (RDB) assay for the rapid and simultaneous genotyping of six mutations (c.95A>G, c.871G>A, c.1004C>T, c.1024C>T, c.1376G>T and c.1388G>A), that were common mutations in the Chinese G6PD deficiency population, and one polymorphism (c.1311C>T). Reliable genotyping of wild-type and mutant genomic DNA samples was achieved by means of a test strip onto which allele-specific oligonucleotide probe lines are fixed in parallel. This method involves a multiplex PCR amplification of three fragments in the G6PD target sequence and a manual hybridization/detection protocol. The entire procedure starting from blood sampling to the identification of mutations requires less than 6 h. The diagnostic reliability of this reverse dot blot assay was evaluated on 207 pre-typed samples by using direct DNA sequence analysis in a blind study. The reverse dot blot typing was in complete concordance with the reference method. The reverse dot blot assay was proved to be a simple, rapid, highly accurate, and cost-effective method to identify common G6PD mutations in Chinese population.

[Clinical phenotype genotype correlation in children with hemoglobin H disease in Zhuhai area of China].

OBJECTIVE: Alpha-thalassemia is one of the most common monogene disorders in the world. Most frequently, it is caused by deletions of alpha-globin gene (-alpha or --), and less commonly resulted from the non-deletional mutation (alpha(T)alpha). Hemoglobin H (HbH) disease is the most severe type among survivors of alpha-thalassemia. The clinical presentation of children with the disease was highly heterogeneous. The aim of this study was to investigate the effect of alpha-globin genotypes in the children with HbH disease on predicting the phenotypic severity and to define the factors involved in the disease progress. METHODS: Forty-three children with the disease in Zhuhai area of Guangdong, China were examined by using established techniques to detect genotypes of alpha-globin and to determine all hematological parameters. All detailed clinical data of the cases were recorded. Then clinical and hematological findings, and the correlation with genotypes were evaluated. RESULTS: Six alpha-thalassemia mutations were detected and interacted to produce 5 HbH disease genotypes. Of these genotypes, -alpha(3.7)/--(SEA)(60%), -alpha(4.2)/--(SEA) (19%) and alpha(CS)alpha/--(SEA) (12%) HbH diseases were prevalent in the area. Compared with -alpha(3.7)/--(SEA) HbH disease, significantly lower red blood cell (RBC) count, hemoglobin (Hb), mean corpuscular hemoglobin (MCHC) and HbA(2) (P < 0.05, 0.01, 0.01 and 0.01, respectively), and significantly higher mean corpuscular hemoglobin volume (MCV) and HbH levels (both P < 0.01), and more severe clinical phenotypes were found in the HbH disease with alpha(T)alpha/--(SEA) genotype. While the differences were much more significant when compared with -alpha(3.7)/--(SEA) then compared with -alpha(4.2)/--(SEA) not only in the hematological parameters, but also in the severity of clinical phenotypes. In addition, HbH levels showed anegatively correlation with the RBC count (r = -0.39, P < 0.01). CONCLUSION: The phenotypes of HbH disease may be mainly related to the underlying genotypes. The children with alpha(T)alpha/--(SEA) genotype presented with more severe hematological and clinical phenotypes followed by the -alpha(4.2)/--(SEA) and then -alpha(3.7)/--(SEA) genotypes. But phenotypic severity was not simply related to the degree of alpha-globin deficiency. HbH levels were found to exacerbate anemia. These data might provide comprehensive and very valuable and basic information for the management of HbH disease, genetic counseling and prenatal diagnosis.