FLUORESCENT IN SITU HYBRIDIZATION (FISH)

 Fluorescent in situ hybridization detects specific nucleic acid sequences in morphologically preserved chromosomes and cells. The technique is based upon the duplex formation of a modified single-stranded DNA fragment (probe) and its complementary sequence (target sequence) in a fixed specimen.  The reaction is detectable by fluorescent microscopy.  The probes currently in use are unique sequence probes for the microdeletion syndrome regions, unique sequences probes for breakpoints of translocations in hematologic malignancies, alpha-satellite probes specific for the centromeric region of all chromosomes, and whole paint chromosome probes.  

REASONS FOR REFERRAL 

·         Individuals suspected of having a microdeletion syndrome: Angelman syndrome, Cri-du-chat syndrome, DiGeorge syndrome, Kallman syndrome, Miller-Dieker syndrome and isolated lissencephaly, Prader-Willi syndrome, Smith-Magenis syndrome, Velocardiofacial (Spritzen) syndrome, Williams syndrome, Wolf-Hirschhorn syndrome (see individual disorders).

·         Prenatal diagnosis in fetuses suspected of aneuploidy of chromosomes 13, 18, 21 and the X and Y chromosomes due to advanced maternal age, abnormal ultrasound findings or abnormal maternal serum screening results (see Aneuploidy Screening).

·         Individuals with a structural rearrangement or a marker chromosome previously unidentifiable by conventional cytogenetic analysis.

·         Individuals with acquired numerical or structural chromosome aberrations for the initial diagnosis or monitoring of residual disease after chemotherapy or bone marrow transplantation (see individual disorders).

TESTING METHODOLOGY

·         The chromosomal DNA is denatured and a specific DNA probe is bound to the denatured target chromosomes or cells. Detection of the probe is by fluorescent microscopy.

·         FISH analysis is based on a minimum of 10 to 20 labeled metaphase spreads or 100 to 500 labeled nuclei.

 SPECIMEN REQUIREMENTS

·         Blood:               Sodium heparin (green top) tubes

Newborn: minimum 1-2 mL

Child/adult: minimum 3-5 mL 

·         Bone Marrow: 0.5-2 mL bone marrow in bone marrow transport media of sodium heparin (green top) tubes.

 ·         Amniotic Fluid: 20-30 mL of amniotic fluid in sterile centrifuge tubes or bottles (discard the first 2 mL collected, syringes not acceptable); inadequate specimens or visibly bloody specimens are not acceptable for aneuploidy screening.

 TURNAROUND TIME: 7 to 10 days for microdeletions, hematologic malignancies,

                                                        structural rearrangements and marker chromosomes

                                           2 to 3 days for prenatal aneuploidy screening

 CPT CODES: 88271, 88273 or 88275, 88230 or 88233 or 88237, 88291

SYNDROME             CLINICAL                             PROBE/                      %CASES                                                                                                           FEATURES                           CHROMOSOME       WITH                                                                                                                                                           LOCUS                       DELETION

Angelman                  Ataxia                                          SNRPN/                      70%

                                    Inappropriate Laughter             15q11.2          

                                    Mental Retardation                  

Cri du Chat                High-pitched Cry                        D5S23/                        > 99%

                                    Microcephaly                              5p15

                                    Mental Retardation                                                      

DiGeorge                    Dysmorphic Facies                   TUPLE1/                     > 95%

                                    Hypoplasia or Aplasia of          22q11.2

                                    Parathyroid/Thymus

Kallman                      Hypogonadotropic                    KAL/                           unknown

                                    hypogonadism, Anosmia          Xp22.3

Miller-Dieker              Dysmorphic Facies                   D17S379/                     > 90%

(Lissencephaly)        Seizures                                        7p13.3

Prader-Willi               Neonatal Hypotonia                  SNRPN/                      70%

                                    Obseity                                        15q11.2

                                    Hypogonadism

                                    Mental Retardation

Smith-Magenis         Dysmorphic Facies                   D17S29/                      99%

                                    Mental Retardation                   17p11.2

Velocardiofacial        Conotruncal Cardiac Defect    TUPLE1/                     > 70%

Syndrome                   Hypernasal Speech                  22q11.2

Williams                     Dysmorphic Elfin Facies          ELN/                            > 95%

                                    Cardiac Defect, MR                   7q11.23

Wolf-Hirschhorn      Dysmorphic Facies                   D4S96/                        >99%

                                    Mental Retardation                   4p16.3