Cytogenetic & Molecular Genetic
Studies in the Neonatal Period

 

Reviewed by Salim Aftimos
June
2011
Clinical Guidelines Back Newborn Services Home Page

Note: Given the increasing concerns around genetic testing without informed consent, only tests for diagnostic or management reasons should be carried out in the neonatal period.

Cord Blood

  • Confirmation of suspected chromosomal disorder following abnormal antenatal ultrasound undertaken late in pregnancy or where further investigation declined during in the pregnancy.
  • Chromosome mosaicism found at CVS, amniocentesis or cordocentesis (where indicated)
  • DNA studies. Cord blood confirmation of single gene disorder suspected on ultrasound findings eg achondroplasia
    Testing for late onset disorders should not be undertaken
  • Confirmation of biochemistry where prenatal diagnosis of a known condition undertaken (requested by testing lab)

Neonatal Testing

  • Blood
  1. Clinical features consistent with known chromosomal abnormality.
  2. Multiple congenital anomalies consistent with possible chromosomal abnormality
  3. Ambiguous genitalia.

WHICH TEST TO REQUEST:
When the phenotype indicates a common aneuploidy (trisomy 21, 18, 13, or X aneuploidy) request a standard karyotype. If an urgent result is required, specify “Rapid FISH Analysis” on laboratory request form and identify the particular chromosome in question (trisomy 21, 18, 13, X monosomy). Click here for link to LabPlus test guide, for turnaround times.

In a baby with dysmorphism/abnormal neonatal adaptation/organ anomalies where a specific diagnosis is not apparent: request a standard karyotype (link to test guide).

If a specific diagnosis is unlikely to alter management, consider an alternative request for a molecular karyotype (link to test guide). If in doubt, please liaise with the clinical geneticist on call.

Where the phenotype suggests a specific microdeletion syndrome, particularly the 22q microdeletion syndrome, request the specific FISH test (rapid test also available for urgent 22q microdeletion requests, link to test guide).

N.B: If Prader-Willi syndrome is suspected, request the methylation test for the 15q11.2-13 locus. For details on turnaround times, please click here. If clinical suspicion is high and a quicker result is desired, consider requesting the specific FISH test, keeping in mind that deletions account for 65-75% of patients with PWS.

  • Solid Tissues
  1. Products of conception.
  2. Post mortem - (1) - (3) as above.

Guidelines for DNA Studies in the Neonatal Period

  • Features of a single gene disorder/syndrome (for diagnostic purposes) e.g. hypotonia
  • Mitochondrial myopathy syndrome.
  • Features of possible single gene disorder where infant may die and genetic testing may later become available (DNA storage)

Blood Collection Tubes