45,X/47,XXX Mosaicism and Short Stature

Systematic analysis of the causes of NIPS sex chromosome aneuploidy false-positive results

OBJECTIVE

To investigate the underlying causes of false positives in NIPT of fetal sex chromosomal aneuploidies using fetal cell-free DNA from maternal plasma.

METHODS

In the present study, we focus on a cohort of 23,984 pregnancy cases with NIPT. Karyotyping and FISH analysis were employed to verify the NIPT detected false-positive results of fetal sex chromosomal aneuploidies, and a comparative CNV sequencing on positive and negative NIPT cases was uniquely performed to elucidate the underlying causes.

RESULTS

A total of 166 cases (0.69%) were identified as fetal sex chromosomal abnormalities, while 84 cases were found to be false-positive results possibly associated with maternal X chromosomal aneuploidies (n = 8), maternal X chromosomal structural abnormalities (n = 1), maternal CNVs (n = 4) as well as known placental mosaicism (n = 1). Furthermore, our study showed that the maternal chromosome CNV between 1-1.6 Mb was associated with false-positive NIPT results in sex chromosomal abnormalities.

CONCLUSION

Our research demonstrated the spectrum of factors causing false positives in NIPT of fetal sex chromosomal abnormalities based on a large cohort. The effective maternal CNV size cut-off identified in our study could integrate into bioinformatics algorithms for reducing the false-positive rate, however, further investigation is necessary to confirm this.

Ovarian reserve evaluation in a woman with 45,X/47,XXX mosaicism: A case report and a review of literature

Background

Turner syndrome (TS) is a common chromosomal disorder affecting approximately 1:2,500 live female births. Mosaic 47,XXX karyotype is found in 3%–4% of TS patients. TS phenotype in rare 45,X/47,XXX mosaicism patients is milder than in classic TS, however their ovarian function, especially in the mature age, has not been described in detail.

Methods

A case report and literature review.

Results

A 30‐year‐old woman with menstrual irregularity and primary infertility presented with short stature and multiple nevi on the face without other common TS clinical features. She had spontaneous puberty and menarche but diminished ovarian reserve at the age of 30. Fluorescence in situ hybridization (FISH) indicated 45,X/47,XXX mosaicism, which was once misdiagnosed as 45,X monosomy. Literature review revealed the prevalence of short stature in only 64.3% of 45,X/47,XXX mosaicism cases, that is, much less frequently than in pure 45,X monosomy. The risk of premature ovarian insufficiency in 45,X/47,XXX mosaicism patients is higher, and ovarian failure is usually observed at around 30 years of age.

Conclusion

FISH should be recommended to evaluate low proportion mosaicism in similar cases. Due to the risk of ovarian failure, fertility preservation for patients with 45,X/47,XXX mosaicism at a younger age must be considered.

An Optimized Method for Accurate Fetal Sex Prediction and Sex Chromosome Aneuploidy Detection in Non-Invasive Prenatal Testing

Massively parallel sequencing (MPS) combined with bioinformatic analysis has been widely applied to detect fetal chromosomal aneuploidies such as trisomy 21, 18, 13 and sex chromosome aneuploidies (SCAs) by sequencing cell-free fetal DNA (cffDNA) from maternal plasma, so-called non-invasive prenatal testing (NIPT). However, many technical challenges, such as dependency on correct fetal sex prediction, large variations of chromosome Y measurement and high sensitivity to random reads mapping, may result in higher false negative rate (FNR) and false positive rate (FPR) in fetal sex prediction as well as in SCAs detection. Here, we developed an optimized method to improve the accuracy of the current method by filtering out randomly mapped reads in six specific regions of the Y chromosome. The method reduces the FNR and FPR of fetal sex prediction from nearly 1% to 0.01% and 0.06%, respectively and works robustly under conditions of low fetal DNA concentration (1%) in testing and simulation of 92 samples. The optimized method was further confirmed by large scale testing (1590 samples), suggesting that it is reliable and robust enough for clinical testing.