Prenatal UPD testing survey in Robertsonian translocations

Risk estimation of uniparental disomy of chromosome 14 or 15 in a fetus with a parent carrying a non-homologous Robertsonian translocation. Should we still perform prenatal diagnosis?

OBJECTIVE

Uniparental disomy (UPD) testing is currently recommended during pregnancy in fetuses carrying a balanced Robertsonian translocation (ROB) involving chromosome 14 or 15, both chromosomes containing imprinted genes. The overall risk that such a fetus presents a UPD has been previously estimated to be around ~0.6-0.8%. However, because UPD are rare events and this estimate has been calculated from a number of studies of limited size, we have reevaluated the risk of UPD in fetuses for whom one of the parents was known to carry a nonhomologous ROB (NHROB).

METHOD

We focused our multicentric study on NHROB involving chromosome 14 and/or 15. A total of 1747 UPD testing were performed in fetuses during pregnancy for the presence of UPD(14) and/or UPD(15).

RESULT

All fetuses were negative except one with a UPD(14) associated with a maternally inherited rob(13;14).

CONCLUSION

Considering these data, the risk of UPD following prenatal diagnosis of an inherited ROB involving chromosome 14 and/or 15 could be estimated to be around 0.06%, far less than the previous estimation. Importantly, the risk of miscarriage following an invasive prenatal sampling is higher than the risk of UPD. Therefore, we do not recommend prenatal testing for UPD for these pregnancies and parents should be reassured.

Complete hydatidiform mole and a coexistent fetus following ovulation induction in a patient with Sheehan's syndrome: a first case report and review of literature

Pregnancy in Sheehan's syndrome (SS) is extremely rare. We present the first reported case of twin pregnancy with complete hydatiform mole (CHM) and a coexistent fetus (CHCF) in a patient with SS. A 29-year-old Chinese patient with SS became pregnant following one cycle of ovulation induction with human menopausal gonadotropin after secondary infertility. A normal live fetus and a low echogenic mass suspected hydatidiform mole (HM) were detected by ultrasound examinations at gestational week 8. The couple highly desired to continue the pregnancy because it is very hard to get pregnant for the patients with SS. However, the pregnancy was terminated for the size of the HM component increased rapidly at gestational week 15. Histological examinations confirmed CHCF. Genetic studies showed that the CHM genome was derived from paternal diploidy, and the normal fetus was from biparental genomes. Furthermore, a literature review on these topics is included. This case highlighted that even in a patient with SS, twin pregnancy with CHCF can still occur after ovulation induction.

Unbalanced and balanced acrocentric rearrangements involving chromosomes other than chromosome 21 at amniocentesis

OBJECTIVE

To investigate unbalanced and balanced acrocentric rearrangements involving chromosomes other than chromosome 21 at amniocentesis.

MATERIALS AND METHODS

From January 1987 to September 2009, 31,194 amniocenteses were performed at Mackay Memorial Hospital, Taipei, Taiwan. Two cases with unbalanced acrocentric rearrangements involving chromosomes other than chromosome 21 from two families, and 24 cases with balanced acrocentric rearrangements involving chromosomes other than chromosome 21 from 21 families were diagnosed and investigated.

RESULTS

We detected i(13q13q), +13 (one case), rob(13q14q), +13 (one case), rob(13q14q) (16 cases), rob(14q15q) (five cases), rob(13q15q) (one case), rob(15q22q) (one case), and mosaic rob(14q22q) (one case). Of the 25 cases that underwent parental cytogenetic investigation, six arose de novo and 19 were inherited (10 maternal and nine paternal). The 16 families with an inherited Robertsonian translocation included rob(13q14q) (11 families), rob(14q15q) (four families), and rob(15q22q) (one family). Of these 16 families, only two had known parental carrier status prior to the first amniocentesis, while the other 14 were aware of a parental carrier status only after prenatal diagnosis of a fetus with a heterologous Robertsonian translocation. The 18 fetuses with balanced heterologous Robertsonian translocations inherited them from six maternal carriers of rob(13q14q), four paternal carriers of rob(13q14q), four paternal carriers of rob(14q15q), and one maternal carrier of rob(15q22q). Neither UPD14 nor UPD15 was detected in any of the 16 cases tested for UPD.

CONCLUSION

Concerning acrocentric rearrangements involving chromosomes other than chromosome 21, we found a frequency of 0.0064% for unbalanced rearrangements and 0.0769% for balanced rearrangements at amniocentesis in this study. rob(13q14q) was the most common and rob(14q15q) the second most common rearrangement. Of the families with an inherited translocation, 87.5% were aware of parental carrier status only after prenatal diagnosis of a fetus with a translocation by amniocentesis.

Risk estimates for uniparental disomy following prenatal detection of a nonhomologous Robertsonian translocation

Carriers of nonhomologous Robertsonian translocations (ROB) are at risk for having offspring with uniparental disomy (UPD). Although risk estimates have been calculated in several independent studies, the estimates have not been optimal because most studies are not of sufficient size and UPD events are rare. However, these collective data have provided the opportunity to derive an overall risk estimate for UPD in the fetus after the prenatal identification of a ROB.

Prenatal search for UPD 14 and UPD 15 in 83 cases of familial and de novo heterologous Robertsonian translocations

OBJECTIVES

The presence in the conceptus of a Robertsonian translocation predisposes to UPD formation, mainly by post-zygotic events of chromosome abnormality rescue. This is due to the increased risk of generating aneuploid zygotes because the rearranged chromosome and the respective homologues are prone to non-disjunction errors. Given this, carriers and karyotypically normal individuals conceived from a parent with a Robertsonian translocation are at risk for UPD. Abnormal phenotypes due to an imprinting effect have been found to be associated with UPD 14 and 15. The aim of the study was to refine, at the time of prenatal diagnosis, the risk for UPD 14 and 15 in a population with Robertsonian translocations involving these chromosomes.

METHODS

Sixty-five cases of familial and de novo heterologous Robertsonian translocations involving chromosomes 14 and 15 and 18 fetuses with a normal karyotype, but conceived by a Robertsonian translocation carrier were prenatally studied to investigate the presence of UPD for chromosomes 14 and 15.

RESULTS

Of the 65 Robertsonian translocation carriers, one fetus with a de novo der(14;21) showed maternal UPD 14. None of the 18 fetuses with a normal karyotype had UPD.

CONCLUSION

Our data, combined with other previous prenatal investigations provide a general risk estimate for UPD 14 and 15 of 0.6%. Nevertheless, combining our data and those previously reported, all three fetuses with UPD had a de novo Robertsonian translocation, thus suggesting a risk of UPD formation of about 3% for this specific group of translocation carriers.

Uniparental disomy and Robertsonian translocations: risk estimation and prenatal testing

BACKGROUND

Uniparental disomy (UPD) is defined by the inheritance of both homologous chromosomes from only one parent, resulting in an imbalance of the expression of imprinted genes. With the recent identification of several diseases associated with UPD, the diagnostic significance of this molecular finding is a focus of interest. Acrocentric chromosomes involved in Robertsonian translocations (RTs) are particularly prone to being affected by mis-segregation events, possibly resulting in UPD. While UPDs of chromosomes 13, 21, and 22 have no clinical consequences, and therefore have no diagnostic impact despite of homozygosity of recessive alleles, prenatal testing for UPDs 14 or 15 is becoming increasingly asked for.

METHODS

Thirty-one fetuses with nonhomologous balanced RTs involving chromosome 14 were tested for UPD14 by microsatellite typing.

RESULTS

No cases of maternal UPD14 were detected among the 31 fetuses analyzed.

CONCLUSIONS

Based on our own data from molecular testing in 31 prenatal RT cases and findings in the published literature, we delineated a risk of 0.3% for a UPD with clinical consequences for prenatally detected carriers of a nonhomologous RT. Prenatal UPD testing is not associated with any additional risk to the pregnancy once invasive prenatal testing has been carried out. However, the possibly conflicting consequences in the case of a prenatal UPD identification should be discussed in advance. Furthermore, risk figures in specific clinical cohorts, such as couples prior to intracytoplasmic sperm injection, as well as questions of prenatal diagnostic management, will be discussed.

Uniparental disomy in fetuses diagnosed with balanced Robertsonian translocations: risk estimate

Forty-two fetuses with non-homologous Robertsonian translocations were analyzed for uniparental disomy (UPD). One fetus with a de novo translocation t(13q;14q) had maternal isodisomy of chromosome 14. In a summary of the published data (including the present study), 315 cases were analyzed for UPD after prenatal diagnosis of balanced Robertsonian translocations, of these two fetuses had UPD, giving a risk estimate of 0.65% (CI 0.2-2.3). This risk justifies the recommendation of UPD analysis in fetuses diagnosed prenatally with Robertsonian translocations, with the emphasis on the chromosomes known to contain imprinted genes, such as 14 and 15. We also discuss the possibility of UPD in offspring of Robertsonian translocation carriers with normal karyotype. Based on the risk for UPD in fetuses with Robertsonian translocation we suggest to test these fetuses for UPD and to do so on amniocytes rather than chorionic villi when the risk for unbalanced karyotype is approximately 1%, comparable to the risk for UPD.