External quality assessment of rapid prenatal detection of numerical chromosomal aberrations using molecular genetic techniques: 3 years experience

Desirable quality-control materials for the establishment of qualified external quality assessment on prenatal diagnosis of chromosomal aneuploidies

OBJECTIVE

To prepare desirable quality-control materials for the establishement of qualified external quality assessment on fluorescence in situ hybridization (FISH)-detected prenatal diagnosis of chromosomal aneuploidies.

METHODS

Four types of amniotic fluid cell suspensions (13-trisomy, 18-trisomy, 21-trisomy and 47,XXY) were mixed together by ratio to produce mosaicism with the percentages of each aneuploidy as 10%, 20%, 30% and 40%, respectively. After being stored in liquid nitrogen of -196 °C for six months, randomly selected samples were incubated in 37 °C water, followed by cultivation, hypo-osmosis and fixation. Finally, FISH detetion was applied on them before and after external laboratory mailing, in step with detection on conventional case samples.

RESULTS

Before mailing, the positive rates of each aneuploidy described above were 12.8%, 23.6%, 33.8%, 44.0%, while 12.6%, 23.8%, 34.0%, 43.5% after mailing. t-test, criteria for stability assessment of quality-control materials in CANS-GL03:2006, showed no significant effect of external mailing on mosaicism since corresponding t values are lower than threshold with significance level α as 0.05 and degree of freedom as 10.

CONCLUSION

As FISH detection showed, the mosaic cell strains prepared in current study exhibited excellent stabilities after cryopreservation in -196 °C, subculture, hypo-osmosis, fixation and external laboratory mailing, demonstrating them as reliable and promising quality-control materials for the establishment of a qualified external quality assessment on prenatal diagnosis of chromosomal aneuploidies.

An external quality assessment scheme for prenatal detection of rare chromosomal abnormalities

OBJECTIVE

To improve the accuracy of prenatal cytogenetic diagnosis by establishing an external quality assessment (EQA) scheme for rare, or subtle, structural chromosomal abnormalities.

METHOD

Typical metaphase images of rare chromosomal abnormalities along with an anonymized clinical history were sent to 35 prenatal diagnosis laboratories. The laboratories were required to provide independent reports using current nomenclature. Evaluation of reports was based on established criteria for quality assessment of karyotype analysis.

RESULTS

Totally 6 kinds of typical rare chromosomal abnormalities were collected. 35 laboratories were enrolled with a response rate of 94.29%. The overall analytical accuracy is 82.20%. This is comparable with our former EQA scheme using established lymphocyte cell lines with rare abnormal chromosome karyotypes (χ²=0.065, P=0.799).

CONCLUSION

Introduction of efficient EQA for prenatal genetic diagnosis is currently imperative, due to the limited performances of karyotype analysis of rare chromosomal abnormalities. Metaphase images could be used as a simple and effective material for EQA and to improve the quality of prenatal genetic diagnosis.

Detection of α-globin gene deletions using denaturing high-performance liquid chromatography and multiplex ligation-dependent probe amplification

BACKGROUND

Multiplex ligation-dependent probe amplification (MLPA) has been used to detect deletions and mutations of the α-globin gene for diagnosis of α-thalassemia. MLPA reaction products are usually separated and analyzed by high-voltage capillary gel electrophoresis (CGE). The goal of this study was to find and use a cost-effective method to separate and analyze MLPA products.

METHODS

Blood samples were collected from China. DNA was extracted and amplified by PCR using fluorescently labeled primers. In this study, denaturing high-performance liquid chromatography (DHPLC) was used to separate and analyze the reaction products. And the optimal separation conditions were determined using nondenaturing columntemperature.

RESULTS

The DHPLC conditions were optimized and have been applied to separate MLPA products and 27 of the MLPA products from 50 to 320 bp were well separated. DHPLC was able to separate up to 37 reaction products that differed by 4-12 base pairs and detected target gene deletions by differences in peak size. Compared with CGE, both the specificity and sensitivity of DHPLC for the 107 DNA samples were 100%.

CONCLUSIONS

DHPLC could be used to test routinely for α-globin gene mutations and deletions. Combined with MLPA, DHPLC is a low-cost, simple to use, accurate technique with practical value.