Wednesday, July 17, 2013

Genetic Counseling Update

We met with a genetic counselor from NYU as scheduled on Thursday of last week.  She began the session by explaining that 1 out of 500 people in the general population have a balanced translocation, which predisposes them to conceptions with too much or too little information (i.e., an unbalanced translocation).  She then went on to state that although we were referred for genetic counseling due to the labs resulting from our miscarriage, she suspects it is highly unlikely that either my husband or I possess a translocation.  But, the genetic testing would definitively answer that question for us, and since more information is better than less, this is the reason my OB referred us for counseling even though this was "only" {I use that word begrudgingly here} our first loss.  I guess in many cases, due to either lack of insurance or lack of testable tissue samples, conclusive results are not often available for "first time" miscarriages.  I guess this means we should consider ourselves lucky that we have the opportunity to get more information about what caused our first loss?  I certainly don't feel that way.  I wish we we weren't in this position at all.  But I digress...

She sympathetically and astutely admitted that knowing the reason for the miscarriage or being tested ourselves wouldn't lessen the pain or sadness of our loss, and when she was done summarizing why we were sitting before her and how she could try to help us get information, she asked if we had any questions.  Of course the only question I could muster at that point was "May I have a tissue" since I was already crying, 5 minutes into the appointment.

Our counselor then summarized the lab report for us and explained that 20 cells were tested from our fetal tissue sample.

In 13 of the cells, there was a structural abnormality found known as a balanced Robertsonian Translocation of chromosomes 14 & 15.  A "translocation" is a form of structural abnormality where a portion of one chromosome is transferred to another chromosome.  There are two main types of translocations -- in a "Robertsonian" translocation, an entire chromosome has attached to another at the centromere.  Because this translocation was "balanced", all of the genetic information was present, but rearranged.

Here is a good description if, like us, you're new to this topic {I've indicated with bold font the parts relevant to our fetal tissue results}:
Structural chromosomal anomalies consist of a defect in the structure of 1 or more chromosomes. Translocation is a type of structural abnormality in which parts of chromosomes end up in the wrong location.  Translocations may be reciprocal or Robertsonian. In a reciprocal translocation, pieces from 2 nonhomologous chromosomes have switched places with each other; in a Robertsonian translocation, 2 acrocentric chromosomes -- that is, chromosomes with essentially a single long arm rather than the more normally encountered long and short arms -- are fused together. The acrocentric chromosomes are 13, 14, 24, 15, 21, and 22. In a balanced structural chromosomal anomaly the amount of chromosomal material present is normal, but the configuration is abnormal. An individual carrying a balanced rearrangement would usually not have any phenotypic effect, except for the possibility of impaired fertility and reproduction. Structural chromosomal abnormalities occur in about 1 of 500 persons. These structural defects may be passed from parent to child; therefore, when a structural anomaly (balanced or unbalanced) is found in a fetus or in an individual, karyotype analysis of parents and possibly other relatives is indicated.
This explains why we were referred for karyotyping.  But, we did manage to have the wherewithal to ask the counselor whether Robertsonian translocations could be sporadic mutations (i.e., not inherited) and indeed they can be.  So, we're hoping that's what happened here and that we will not experience this abnormality in future pregnancies.  However, since all the proper genetic material is present in a balanced translocation, it would not cause a miscarriage.


In 7 of the cells, there was a numerical chromosomal abnormality found known as a "trisomy", which is the presence of extra chromosomes resulting from segregation errors during cell division.  In other words, there are three copies of a particular chromosome instead of the normal two.  In our case, our fetus had "Trisomy 14".  This is known as an "unbalanced" chromosomal arrangement because there is either too much or too little information present.  As with most trisomies and all unbalanced arrangements, this abnormality is not compatible with life.  Here is an example of what a trisomy looks like:
The slightly reassuring news here is that numerical abnormalities are sporadic (i.e., not inherited), and they do not usually recur in subsequent pregnancies.  According to one source, "In the case of a numerical chromosomal anomaly in a fetus, parental chromosomes are usually normal, so karyotype analysis of the parents is not indicated. The recurrence risk for a chromosomal anomaly following the diagnosis of trisomy in a pregnancy is thought to be about 1%."  I hope this statistic holds true and we are not unlucky enough to experience this abnormality again in a future pregnancy.


After meeting with the counselor, we each had one vile of blood drawn and are now anxiously awaiting the results of the karyotyping, which should take approximately 2-4 weeks.

Please keep your fingers crossed for us...

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