Why does a balanced translocation not cause health problems in the person who ca

[Anonymous]

Why does a balanced translocation not cause health problems in the person who carries it?

[Genetic Counselor]

The carrier remains healthy because every gene is still present and, in most cases, still capable of functioning normally the rearrangement changes the location of chromosomal segments, not their content. Since the cell’s total genetic instructions are complete, protein production and normal development proceed without disruption.

There are, however, specific extreme rare situations where a carrier can be clinically affected:

*Breakpoint disruption of a gene – if the point where the chromosome breaks happens to fall within an important gene rather than between genes, that gene can be disrupted and may not function correctly.
*Position effect – a gene may be moved to a new chromosomal neighbourhood where nearby regulatory elements alter how strongly or weakly it is switched on, even though the gene itself is intact.
*Disruption of imprinted regions – some genes are expressed differently depending on whether they are inherited from the mother or the father. If a translocation involves a chromosomal region subject to this parent-of-origin effect (called genomic imprinting), it can occasionally cause clinical features even though the rearrangement is balanced.

Apart from these exceptions, which are relatively uncommon, most balanced translocation carriers have normal physical and intellectual development. In clinical practice, carriers are most often identified for one of three reasons: they are undergoing an infertility work-up, they have experienced recurrent pregnancy loss, or they have had a child diagnosed with an unbalanced chromosomal condition, which prompts testing of the parents.

[Author]

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