PPM – Chromosome and FISH Analyses of Patients with Suspicion of Turner Syndrome-Chromosome and FISH Analyses Checklist

Chromosome and FISH Analyses Checklist

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This document provides a checklist for conducting chromosome and FISH (fluorescence in situ hybridization) analyses on patients suspected of having Turner Syndrome. The checklist includes instructions for reviewing patient history and requisition forms, as well as specific steps to follow depending on the type of specimen being analyzed (prenatal or postnatal).<br /><br />For prenatal specimens, there are guidelines for examining additional cells or colonies in certain situations, such as when a 45,X karyotype is observed in multiple cells or colonies, or when a structurally abnormal X chromosome or a small marker/ring chromosome is present. It is recommended to perform FISH testing using X/Y centromere probes to determine the origin of the marker chromosome or to look for the presence of XIST gene.<br /><br />The checklist also highlights the importance of having normal cut-off values for interphase FISH analysis in normal controls for both males and females. In the case of postnatal testing, additional cells should be examined if a structurally abnormal X chromosome is identified, and a minimum of 200 interphase cells should be analyzed for X/Y centromere FISH testing.<br /><br />If a small marker or ring chromosome of X origin is observed, further testing for the presence of XIST gene is recommended. The laboratory should establish appropriate databases with normal cut-off values for Y chromosome signal in interphase cells for postnatal testing.<br /><br />Additionally, if Turner Syndrome is strongly suspected phenotypically but a 46,XX karyotype is observed, follow-up studies for mosaicism should be considered, which may involve FISH or assessment of a different tissue type.<br /><br />The document emphasizes the importance of including a referral for genetic consultation in the report.

Keywords

chromosome analysis

FISH analysis

Turner Syndrome

patient history

requisition forms

prenatal specimens

postnatal specimens

X/Y centromere probes

interphase FISH analysis

genetic consultation