Inheritance of a Chromosome 3 and 21 Translocation in the Fetuses, With One Also Having Trisomy 21, in Three Pregnancies in One Family

Abstract

The majority of chromosome rearrangements are balanced reciprocal and Robertsonian translocations. It is now known that such abnormalities cause no phenotypic effect on the carrier but lead to increased risk of producing unbalanced gametes. Here, we report the inheritance of a translocation between chromosomes 3 and 21 in a family with one of two fetuses with Down Syndrome carrying the same translocation and the other also carrying the same translocation without the additional chromosome 21. Chromosomal analysis from fetal amniotic fluid and peripheral blood lymphocytes from the family were performed at the Çukurova University Hospital at Adana, Turkey. We assessed a family in which the translocation between chromosomes 3 and 21 segregates: one of the three progenies carried the 47,XX,+21,t(3;21)(q21;q22) karyotype and presented with Down Syndrome; another of the three progenies carried the 46,XX,t(3;21) (q21;q22) karyotype and the third had the 46,XY karyotype. Their mother is phenotypically normal. Apparently this rearrangement occurred due to an unbalanced chromosome segregation of the mother [t(3;21)(q21;q22)mat]. This family will enable us to explain the behavior of segregation patterns and the mechanism for each type of translocation from carrier to carrier and their effects on reproduction and numerical aberrations. These findings can be used in clinical genetics and may be used as an effective tool for reproductive guidance and genetic counseling.

Antenatal Detection of Trisomy 21 from Mosaic Translocation in Uncultured Amniocytes by Interphasic FISH

“…Concerning translocation 21q, in most cases, children do not exhibit any morphological anomalies [1]. However, there is a risk of 5% to 10% of having an abnormal phenotype as it is the case in the present observation.…”

“…In this case, the risk of having repetitive spontaneous miscarriages or children with Down syndrome is 100% [15,16]. In the event of parental mosaicism, the risk of recidivism is greater than in a normal population [1]. This explains why a karyotype of parents, followed by a genetic counselling had been proposed.…”

“…Translocation may be de novo with a recurrence of 1%, or inherited from one of the parents and therefore not in relation with advanced maternal age (both parents are often the youngest) [3]. In an inherited form, recurrence (relatively high) is 20% if it is the mother who is involved and 10% if it is the father who is carrier of the anomaly [1]. In addition, chromosomal rearrangement especially balanced and Robertsonian translocations whose give higher risk of aneuploidy, are the most common anomalies found in couple having repetitive spontaneous abortions [1,12].…”

“…In an inherited form, recurrence (relatively high) is 20% if it is the mother who is involved and 10% if it is the father who is carrier of the anomaly [1]. In addition, chromosomal rearrangement especially balanced and Robertsonian translocations whose give higher risk of aneuploidy, are the most common anomalies found in couple having repetitive spontaneous abortions [1,12].…”

“…The trisomy 21 or Down syndrome is the most common chromosomal disorder with the incidence estimated between 1/700 to 1/1000 live births, with a high risk in strong correlation with advanced maternal age [1,2]. The frequency is constant, regardless of the ethnic groups and the socio-economic conditions.…”