Indications for telomere testing

1) Unexplained developmental delay or mental retardation is the most common indication for telomere screening. 

Several studies have investigated the incidence of telomere rearrangements in individuals with unexplained mental retardation and it is estimated to be ~ 6.6% (ref).  The American Academy of Neurology has recently issued a practice parameter statement regarding the evaluation of a child with global developmental delay and recommends telomere analysis as part of that comprehensive evaluation (Neurology 2003;60:367-380).
  ( discuss routine cyto missing rearrangements)

2) Parents of a child with a telomere abnormality

Up to 50% of telomere case may be inherited; therefore, we recommend parental analysis of all individuals who carry a telomere rearrangement.  In some instances a normal parent may carry a balanced form of the telomere rearrangement called a balanced translocation, which involves the exchange of pieces between two chromosomes. All of the genetic material is present, but in the wrong location.  Carriers of balanced translocations are usually normal and are not clinically affected. However, carriers of balanced translocations have a 50% chance of passing on an unbalanced translocation, which results in the loss of a chromosome segment and a gain of another chromosome segment. Unbalanced translocations often result in an abnormal pregnancy outcome (miscarriage or affected child).

Parental analysis may detect the presence of a benign polymorphism. A benign polymorphism is a change that does not result in any clinical abnormalities and likely represents a normal variation in the population.  If a normal parent carries the identical rearrangement as the affected child, the rearrangement is more likely to be a benign polymorphism and not the source of the problems in the child.

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3) Prenatal screening
a. If a parent is found to be a carrier of a telomere abnormality, prenatal screening can be performed on any future pregnancies.  This prenatal screening would involve the use of routine amniocentesis or chorionic villus sampling (CVS) at a local obstetrician?s office. The sample could then be sent to a laboratory performing telomere analysis.

4) Refining an abnormality on routine cytogenetic analysis
Targeted telomere analysis may help to define an abnormality found on routine cytogenetic analysis.  Occasionally, unidentified extra chromosome material may be noted at the end of a chromosome or as an extra marker or ring chromosome. Telomere probes may used to identify which chromosome the extra material is from or if any deletions of the reciprocal chromosome have occurred.