Risk estimates for balanced reciprocal translocation carriers--prenatal diagnosis experience

Clinical outcomes for couples containing a reciprocal chromosome translocation carrier without preimplantation genetic diagnosis

OBJECTIVE

To evaluate the pregnancy outcomes of couples containing a carrier of a reciprocal chromosome translocation (RCT) after assisted reproductive technology without preimplantation genetic diagnosis.

METHODS

A retrospective study was performed using data for couples with an RCT carrier and control couples with a normal karyotype (1:4 ratio) who underwent assisted reproductive technology cycles at a Chinese fertility center in 2010-2011. The embryos were fertilized via in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Only the first pick-up cycles were used for analysis. Clinical variables were compared.

RESULTS

Compared with the control group (n=164), the RCT group (n=41) had a marginally lower clinical pregnancy rate (46.3% [19/41] vs 54.3% [89/164]), implantation rate (21.7% [23/106] vs 26.9% [118/438]), multiple-gestation pregnancy rate (21.1% [4/19] vs 32.6% [29/89]), and delivery rate (36.6% [15/41] vs 47.6% [78/164]), whereas the spontaneous abortion rate was slightly higher (21.1% [4/19] vs 12.4% [11/89]). However, none of these differences were significant.

CONCLUSION

The clinical outcomes for RCT carriers were acceptable after IVF/ICSI without performing preimplantation genetic diagnosis, indicating that this approach might comprise a feasible alternative fertility treatment for RCT carriers.

Reproductive outcome after chromosome analysis in couples with two or more miscarriages: index [corrected]-control study

OBJECTIVE

To compare reproductive outcomes in couples carrying a structural chromosome abnormality and non-carrier couples referred for chromosome analysis after two or more miscarriages.

DESIGN

Index [corrected]-control study.

SETTING

Six centres for clinical genetics in the Netherlands.

PARTICIPANTS

278 carrier couples and 427 non-carrier couples referred for chromosome analysis between 1992 and 2000 after two or more miscarriages before 20 weeks of gestation. Couples were followed up for at least 24 months after chromosome analysis.

MAIN OUTCOME MEASURES

The birth of at least one healthy child, at least one more miscarriage, and viable offspring with unbalanced chromosomal abnormalities after parental chromosome analysis.

RESULTS

Mean follow-up after chromosome analysis was 5.8 years. 120 of 247 (49%) carrier couples had one or more miscarriage after chromosome analysis compared with 122 of 409 (30%) non-carrier couples (difference 19%, 95% confidence interval 11% to 26%; P < 0.01). The percentage of couples with at least one healthy child was not significantly different in carrier couples (83%) and non-carrier couples (84%) (difference -1%, - 7% to 5%). Among 550 pregnancies in carrier couples, two viable unbalanced chromosome abnormalities were detected at prenatal diagnosis (0.4%) and the fetuses aborted and two children with an unbalanced karyotype were born (0.4%).

CONCLUSIONS

Couples whose carrier status was ascertained after two or more miscarriages have a low risk of viable offspring with unbalanced chromosomal abnormalities. Their chances of having a healthy child are as high as non-carrier couples, despite a higher risk of miscarriage.

Risk evaluation of carriers with chromosome reciprocal translocation t(7;13)(q34;q13) and concomitant meiotic segregation analyzed by FISH on ejaculated spermatozoa

We performed the segregation analysis of a relatively large pedigree of t(7;13)(q34;q13) carriers together with the sperm karyotype analysis of the one carrier using a tri-color fluorescence in situ hybridization (FISH) method. The risk assessments for unfavorable pregnancy outcomes in a series of 36 pregnancies in eight reciprocal chromosome translocation (RCT) couples of carriers were estimated directly from a pedigree after ascertainment correction. The individual probability rate for unbalanced child was predicted according to Stengel-Rutkowski and co-workers. The unbalanced karyotypes in the form of monosomy 7q34-->qter and trisomy 13q13-->qter were detected among stillborn/early death newborns with holoprosencephaly (HPE), cyclopia and other malformations. Based on clinical description of unkaryotyped stillbirth progeny, it can be assumed that the phenotype distinctions were connected with the unbalanced karyotype from 2:2 segregation (monosomy 7q with trisomy 13q) and 3:1 segregation as interchange trisomy 13 (Patau syndrome). Probability rates for miscarriages, stillbirth/early death were 12.9 +/- 6% (4/31) and 29 +/- 8.2% (9/31), respectively. The results of the meiotic segregation pattern indicated the rate of unbalanced spermatozoa for about 60%, with the unusual high rate (29.4%) of 3:1 segregant (i.e., 13.4% of the tertiary segregation and 16% of the interchange segregation). Adjacent-1 segregation followed with 23.5% and adjacent-2 followed with 7.2% of analyzed spermatozoa. The high rate of unbalanced gametes in comparison to the number of stillborn/early death and miscarriages detected in pedigree suggests a strong selection against unbalanced chromosomal constitutions during fetal development. It corresponds to a very small probability rate (about 0.3%) of viable unbalanced progeny from 3:1 meiotic segregation predicted for maternal carriers. This knowledge can be used in genetic counseling of families with similar RCT ascertained in a different way.

Severe hypospadias associated with Robertsonian translocation

In this study, we report a 3-year-old boy with severe scrotal hypospadias with Robertsonian translocation [45,XY,t(13q;14q)]. The patient was born at term with a low birth weight and hypospadias. There was no endocrinological abnormality. His father also has a balanced 13-14 Robertsonian translocation. Two-stage hypospadias repair was carried out. The presence of this chromosomal anomaly and hypospadias are unique to our patient, compared to others with the 45,XY,t(13q;14q) translocation. Although no such association has been reported so far, we thought that severe hypospadias in this case might be associated with this translocation.

Genetic counseling in carriers of reciprocal chromosomal translocations involving long arm of chromosome 16

Families with balanced chromosomal changes ascertained by unbalanced progeny, miscarriages, or by chance are interested in their probability for unbalanced offspring and other unfavorable pregnancy outcomes. This is usually done based on the original data published by Stengel-Rutkowski et al. several decades ago. That data set has never been updated. It is particularly true for the subgroup with low number of observations, to which belong reciprocal chromosomal translocations (RCTs) with breakpoint in an interstitial segment of 16q. The 11 pedigrees from original data together with the new 18 pedigrees of RCT carriers at risk of single-segment imbalance detected among 100 pedigrees of RCT carriers with breakpoint position at 16q were used for re-evaluation of the probability estimation for unbalanced offspring at birth and at second trimester of prenatal diagnosis, published in 1988. The new probability rate for unbalanced offspring after 2 : 2 disjunction and adjacent-1 segregation for the total group of pedigrees was 4 +/- 3.9% (1/25). In addition, the probability estimate for unbalanced fetuses at second trimester of prenatal diagnosis was calculated as 2/11, i.e. 18.2 +/- 11.6%. The probability rates for miscarriages and stillbirths/early deaths were about 16 +/- 7.3% (4/25) and <2% (0/25), respectively. Considering different segment lengths of 16q, higher probability rate (0/8, i.e. <6.1%) for maternal RCT carriers at risk of distal 16q segment imbalance (shorter segment) was obtained in comparison with the rate (0/10, i.e. <4.8%) for RCT at risk of proximal segment imbalance (longer segment). It supports findings obtained from the original data for RCT with other chromosomes, where the probability for unbalanced offspring generally increased with decreasing length of the segments involved in RCT. Our results were applied for five new families with RCT involving 16q, namely three at risk of single-segment imbalance [t(8;16)(q24.3;q22)GTG, ish(wcp8+,wcp16+;wcp8-,wcp16+), t(11;16)(q25;q22)GTG, and t(11;16)(q25;q13)GTG] and two with RCT at risk of double-segment imbalance [t(16;19)(q13;q13.3)GTG, isht(16;19)(q13;q13.3) (D16Z3+,16QTEL013-D19S238E+,TEL19pR-; D16Z3-, D19S238E-,TEL19pR+), and t(16;20)(q11.1;q12)GTG, m ish,t(16;20)(wcp16+,wcp20+;wcp16+,wcp20+)]. They have been presented in details to illustrate how the available empiric data could be used in practice for genetic counseling.

Genetic counselling in carriers of reciprocal chromosomal translocations involving short arm of chromosome X

A central concept in genetic counselling is the estimation of the probability of occurrence of unbalanced progeny at birth and other unfavourable outcomes of pregnancy (miscarriages, stillbirths and early death). The estimation of the occurrence probability for individual carriers of four different X-autosome translocations with breakpoints at Xp, namely t(X;5)(p22.2;q32), t(X;6)(p11.2;q21), t(X;7)(p22.2;p11.1), and t(X;22)(p22.1;p11.1), is presented. The breakpoint positions of chromosomal translocations were interpreted using GTG, RBG and FISH-wcp. Most of these translocations were detected in women with normal phenotype, karyotyped because of repeated miscarriages and/or malformed progeny. A girl with very rare pure trisomy Xp22.1-->pter and a functional Xp disomy was ascertained in one family and her clinical picture has been described in details. It has been suggested that not fully skewed X chromosome inactivation of X-autosome translocation with breakpoint positions at Xp22 (critical segment) could influence the phenotype and risk value. Therefore, the X inactivation status was additionally evaluated by analysis of replication banding patterns using RBG technique after incorporation of BrdU. In two carriers of translocations: t(X;5)(p22.2;q32) and t(X;7)(p22.2;p11.1), late replication state of der(X) was observed in 5/100 and 10/180 analysed cells, respectively. In these both cases the breakpoint positions were clustered at the critical segment Xp22.2. In two other cases, one with the breakpoint position within [t(X;22)(p22.1;p11.1)] and one outside the critical region [t(X;6)(p11.2;q21)], fully skewed inactivation was seen. Therefore, we suggest that neither the distribution of the breakpoint positions nor fully skewed inactivation influenced the phenotype of observed t(X;A) carriers. The occurrence probabilities of the unbalanced progeny were calculated according to Stene and Stengel-Rutkowski along with application of updated available empirical data. In the studied group the values of occurrence probability for unbalanced offspring at birth ranged from 2.1% to 17%. Information on the magnitude of the individual figures may be important for women carrying a reciprocal X;A translocation when deciding upon further family planning.

Rapid prenatal diagnosis in translocation carriers by interphase FISH with chromosome-specific subtelomere probes

Interphase fluorescence in situ hybridization (FISH) analysis can provide rapid preliminary analysis of chromosome aneuploidy from direct amniocyte and chorionic villus sample (CVS) preparations. Typically, interphase FISH is used in screening for numerical abnormalities of chromosomes X, Y, 13, 18, and 21. More recently, FISH probe sets became available for the subtelomeric region of each chromosome, allowing screening for terminal chromosome rearrangements. The purpose of the current study was to evaluate the use of dual-color interphase FISH analysis with chromosome-specific subtelomere probes for rapid prenatal diagnosis in 14 pregnancies from 12 different translocation carriers. Interphase FISH analysis was performed on direct CVS or amniocyte preparations from 12 reciprocal translocation and two Robertsonian translocation pregnancies with the appropriate chromosome-specific subtelomere probes for each chromosome involved in the translocation. Analysis of the interphase FISH probe signals predicted balanced or normal segregants in each case, thus rapidly excluding a chromosomally unbalanced segregant. Subsequent metaphase analysis showed normal karyotypes in seven fetuses and balanced translocations in the remaining seven. This series illustrates the utility of interphase FISH analysis with chromosome-specific subtelomere probes for rapid prenatal diagnosis in cases of parental reciprocal translocations and Robertsonian translocations.

Prenatal diagnosis of chromosome disorders in Tunisian population

Cytogenetic prenatal diagnosis (PND) is under national health program in most developed countries, while it concerns a small part of population at risk in developing countries. Finance is common reason of absence of PND development, but socio-cultural believes play an important role in Arab Muslim countries. In this paper we report results of 3110 fetal karyotypes carried out in a Tunisian population, by cultured amniocytes analysis. It is the largest report in a Muslim Arab country in our Knowledge. Abnormal karyotypes rate was 4.18% classified in two groups: bad prognosis (3.05%) and good prognosis (1.13%). Common amniocentesis indication was maternal age. The highest predictive value was observed in balanced karyotype and fetal ultrasound findings indications. Maternal serum markers were not commonly used for trisomy 21 screening. Pregnancy termination that is permitted by legal and religious authorities was accepted by 94,74% parents. Information about PND outcomes was given by genetic counselling prior to fetal sampling, pregnancy interruption was discussed with parents at cytogenetic result announcement. The authors conclude that in order to prevent mental and physical handicap related to cytogenetic disorders we have to promote PND by education for population, genetic counselling and fetal ultrasound screening; all three methods available in Tunisia.