The Constitutional Balanced Translocation t(11;22)(q23;q11.2)-An Indian Account GC01-GC04
Dr. Vivi M Srivastava,
Professor and Head, Christian Medical College, Ida Scudder Road, Vellore-632004, Tamil Nadu, India.
Introduction: The balanced translocation t(11;22) is one of the most common constitutional genetic abnormality detected in humans. Carriers of the t(11;22) are usually phenotypically normal and their carrier status is ascertained only if they present with reproductive losses, infertility or a child with an abnormal phenotype. The t(11;22) translocations are a cumulative effect of recombination errors occurring during meiosis. Children with Emanuel syndrome show a gain of additional genetic material in the form of der(22) chromosome on conventional karyotype inherited either from the carrier parents or de novo in origin. Children with der(22) chromosome presented with microcephaly, hypotonia, preauricular sinus and developmental delay.
Aim: To study the mode of inheritance and outcome of the balanced translocation t(11;22) in the families.
Materials and Methods: A total of 16 individuals from six unrelated families underwent cytogenetic analysis at the Christian Medical College, Vellore, Tamilnadu, India, and their karyotype showed the balanced t(11;22)(q23;q11.2) or a der(22)t(11;22)(q23;q11.2) inherited from a t(11;22) carrier parent. Also, karyogram of the spouses of the carrier individuals were also studied. Conventional cytogenetic analysis of phytohaemagglutinin-stimulated peripheral blood cultures was performed. Fluorescence In Situ Hybridization (FISH) was performed to confirm the der(22) t(11;22)(q23;q11.2).
Results: Seven individuals from six unrelated families showed the balanced t(11;22). These included six adults and one child (five females and two males). All six adult carriers were phenotypicaly normal. In three adults, the translocation was ascertained because their children had abnormal phenotypes. The remaining three adults were from families being investigated for recurrent pregnancy losses. One of these subsequently underwent amniocentesis which showed a translocation morphologically identical to that in the father. All the three carrier parents had children with abnormal phenotypes. And their karyogram showed 47 chromosomes due to gain of a supernumerary chromosome+der(22)t(11;22)(q23;q11.2) of maternal origin, while the fourth child presented with a t(11;22) identical to that of her carrier father, but was lost to follow-up.
Conclusion: It is important to be aware of this balanced translocation and its varied outcomes, so that members of the family can be studied. This would help to determine the mode of inheritance and to predict the likelihood of other carriers in the family having children with chromosomal imbalance.