Definition

Robertsonian Translocation

  • Definition: A Robertsonian translocation is an unusual type of chromosome rearrangement caused by two particular chromosomes joining together. In a Robertsonian translocation, two of the five acrocentric chromosomes have broken at the beginning of the short arm near the point where it meets the long arm. The long arms have then fused together. This chromosome then consists of two long arms but no short arms.
  • Acrocentric chromosomes: Each chromosome has a short arm and a long arm. Five of the 23 chromosomes have a very small short arm that contains no unique genes; these are chromosome 13, 14, 15, 21 and 22. Technically, they are called acrocentric chromosomes.
  • Chromosome number: Robertsonian translocation carriers have 45 chromosomes. In this leaflet we also call the chromosome with the Robertsonian translocation a fused chromosome.
  • Morbidity: Out of every 1,000 newborn babies, one has a Robertsonian translocation. It accounts for about 2% ~ 3% of infertility.

Different embryo types of Robertsonian Translocation Carrier

 

  • Entirely normal embryos: A normal pregnancy and baby. The baby does not inherit the fusion chromosome and has a normal make-up of 46 separate chromosomes.
  • Robertsonian Translocation Carrier: A normal pregnancy and baby but the baby is a carrier. As carriers are healthy and have a normal lifespan, many never discover about their unusual chromosome rearrangement. In fact, the translocation can be passed down in families for many generations without anyone discovering. 
  • Unbalanced embryos: An unbalanced Robertsonian translocation may come to light after a baby is born with a chromosome disorder, such as Translocation Down’s syndrome, or lead to pregnancy loss, either as a miscarriage-often before the pregnancy is recognised - or much more rarely as stillbirth. 

The probability to have a non-Robertsonian translocation embryo

Based on our theoretical calculation, the probability that we can have an entirely normal embryo (46XN) is >60% if a couple has >five embryos.

  • ≥1 Unbalanced embryos=1-(2/6)Number of embryo
  • ≥1 Balanced embryos (Robertsonian Translocation Carrier or Entirely normal embryo) =1-(4/6) Number of embryo
  • ≥1 Entirely normal embryo=1-(5/6)Number of embryo

 

Principle

S-PGDTM for Robertsonian Translocation Carrier Testing

Jabrehoo exclusively provides you with the state-of-the-art NGS-based robertsonian translocation carrier testing solutions

  • SNP genotyping
  • Specific primer design
  • Mutual authentication of Chromosomes
  • NGS technology

 

Benefits

  • Globally First 
    An integrated solution to distinguish entirely normal embryos from those with robertsonian translocation.  
  • Precise
    Design high specificity primer, and choose the SNP loci to build haplotype. Then complete mutual authentication of Chromosomes. The accuracy is higher.
  • Routine
    It’s not to observe cells so that can reduce some unnecessary steps and suitable for different spouse.    
  • Fast
    High-throughput sequencing technologies, and have different sequencing tags, that can analyze a large number of samples at one time.

Simple Clinical Process

  

Target Patients

  • Robertsonian translocation carriers.

Benefits of S-PGDTM for Robertsonian Translocation Carrier Testing 

  • Alternative: After the development of S-PGDTM technology, clinicians will have an additional option to give to Robertsonian translocation carriers when they perform genetic counseling. That is patients can choose to have a baby who has 46 chromosomes.
  • Block the inheritance: The translocation can be passed down in families for many generations. This testing can be offered to ensure that implanted embryos are completely normal embryos.

CASE

Background
The father is a Robertsonian13;14 carrier whose Karyotype is 45, XY, der(13;14). The mother has two separate 13s and two separate 14s whose Karyotype is 46, XX.

We detected 8 embryos(Number respectively is: embryo 1, embryo 2, embryo 3, embryos 4, embryo 5, embryo 6, embryo7, embryo 8) , and the samples are whole genome amplification products from trophoblast cells of blastocyst stage. In addition, the DNA samples of peripheral blood cell came from parents.

Results

  • Embryo 1, Embryo 4, Embryo 5 are entirely normal embryos which carry the haplotype c of chromosome 13 and the haplotype d of chromosome 14.
  • Embryo 2, Embryo 6, Embryo 7, Embryo 8 are Robertsonian translocation carrier which  carry the haplotype C of chromosome 13 and the haplotype D of chromosome 14.
  • Embryo 3 is unbalanced embryos which is Trisomy 14.

What are the risks of having more than one affected pregnancy or child?

This depends chiefly on whether either parent is a Robertsonian translocation carrier. If neither parent is a carrier, it is extremely unlikely that another baby will be conceived with an unbalanced Robertsonian translocation. If the mother is a carrier and her translocation chromosome includes 21, there is an appreciable risk of having another affected pregnancy. For other carriers, the risk is low.

If one parent is a Robertsonian translocation carrier

Mother has 13;21, 14;21, 15;21 or 21;22 10-15% risk of a baby with translocation Down’s.
Mother has 13;14, 13;15, 13;21 or 13;22 1% chance of having a baby with trisomy 13.
Mother has 14;15, 14;22 or 15;22 Almost certainly no risk of having a baby with a trisomy, but possible risk of miscarriage or UPD.
Father with any Robertsonian combination Low risk, below 1%, of any child being affected.

How unusual is it to be a Robertsonian carrier?

Although one person in 1,000 is a Robertsonian carrier, some combinations of the five acrocentric chromosomes are much more common than others.

Robertsonian translocation Approximately how common are carriers?
13;14 1 : 1 ,300
14;21 1 : 12,500
14;15 1 : 20,000
13;13, 13;15, 13;22, 14;22 1 : 50,000
13;21, 15;22 1 : 100,000
15;21, 21;21, 21;22 1 : 200,000