FAQ: Microarray guidelines for health care providers
The relatively recent use of genomic microarrays has provided a unifying genetic diagnosis for approximately 15% of patients with global developmental delay. Microarrays have also become part of the recommended investigations for patients with autism spectrum disorders. Given that microarray has replaced the standard karyotype as a whole genome investigation for these patients, and that the CHEO Genetics clinic currently has a wait-list of 10-12 months for elective patients, some providers have inquired for which patients they should consider ordering a microarray, either prior to, or instead of, a Genetics clinic assessment. Patients with ASD or GDD can also be evaluated in the Metabolics clinic. It is at the discretion of the primary care giver whether they wish to refer the patient to the Genetics clinic or to the Metabolics clinic.
This document aims to provide guidance regarding:
- Which patients should have a genomic microarray, either before or instead of a Genetics clinic assessment.
- What complementary investigations are necessary for children with autism spectrum disorders.
- The procedure to order a genomic microarray.
Which patients should be offered a genomic microarray?
- We would suggest that patients with isolated autism spectrum disorders (who are expected to have delays in language and socialization) be offered a microarray by their pediatrician. For these patients, only those with an abnormal microarray should be referred to the Genetics clinic.
- Patients with autism spectrum disorders and any of the findings below can be offered a microarray by their pediatrician, but should also be referred to the Genetics clinic to assess for single gene conditions:
- Head circumference below the 2nd centile or above the 98th centile
- Failure to thrive or obesity
- Short stature or overgrowth
- Dysmorphic features
- Congenital malformations
- Features of tuberous sclerosis complex on Wood’s lamp examination
- Other individuals in the family with autism, developmental delay or a known single gene syndrome
- We would suggest that patients with isolated global developmental delay (without autism or the findings listed in 2) be offered a microarray by their pediatrician. However, these patients should be referred to the Genetics or metabolic clinic regardless of the results of the microarray.
- Patients with dysmorphic features, congenital malformations or other reasons for referral should be referred to the Genetics clinic because a single gene condition may be identified and a microarray may not be required.
- Patients with a history of recurrent vomiting, lethargy or developmental regression should be referred to Metabolics as opposed to Genetics.
- For any patient it remains at the discretion of the primary caregiver to evaluate if referrals to additional specialties are warranted.
- Please page Genetics if your patient’s mother is pregnant (< 18 weeks). We typically see the child and parents urgently under these circumstances.
How to order a genomic microarray:
For patients with a valid Ontario or Quebec health card (MOHLTC or RAMQ coverage), blood is drawn and sent to the CHEO Cytogenetics Laboratory. Provide your patient with the completed CHEO Cytogenetics Laboratory MICROARRAY and Q-PCR follow-up Requisition.
What to do if the microarray result is abnormal:
- If the microarray shows a clearly pathogenic variation: please refer your patient to the Genetics clinic.
- If the microarray shows a variation of unclear clinical significance and the report requests parental samples:
- Please send the requested parental samples to the laboratory which performed the microarray analysis.
- The original report will indicate:
- Whether a repeat sample on the child is required
- In which type of tube the samples should be sent
- Please refer your patient to the Genetics clinic when parental results become available. If a patient is referred with a microarray report showing a variation of unclear clinical significance, but no parental results (or no explanation if one or both parents are unavailable), the referral will be returned. Copies of the genomic microarray and all other relevant information and investigations need to be attached to the referral.
We will strive to see patients with an abnormal microarray within 3 months after receipt of the referral to:
- Complete a medical genetic assessment
- Counsel the patients and/or their parents
- Discuss whether additional familial studies are indicated.
Should I do any other investigations?
For patients with autism spectrum disorders (males and females), you should:
- Perform a Wood’s lamp examination looking for cutaneous features of Tuberous Sclerosis Complex (TSC)
- Order molecular testing for Fragile X syndrome. Blood is drawn at the CHEO outpatient lab office and sent to the CHEO Molecular Diagnostic Laboratory. Provide your patient with the completed CHEO Molecular Genetics Diagnostic Laboratory Test Requisition.