Title:Pre-implantation Genetic Testing in Inherited Metabolic Diseases? Stateof-the-art and current challenges
Volume: 24
Issue: 16
Author(s): Ana Miguel Capela*, Ana Cunha, Ana Maria Fortuna and Cláudia Falcão Reis
Affiliation:
- Unidade de Genética Médica, Centro de Genética Médica Jacinto Magalhães - Centro Hospitalar Universitário de
Santo António, Portugal
Keywords:
Inborn errors of metabolism (IEM), Preimplantation genetic testing (PGT), mtDNA, Assisted Reproductive Techniques (ART), Genetic counselling
Abstract: Introduction: Inborn errors of metabolism (IEM) are genetic diseases involving congenital
disorders of enzyme activities. Most follow Mendelian autosomal recessive inheritance
and few follow mitochondrial inheritance. In many cases, after the birth of an affected child
parents discover that have been the carriers for the condition and worry about the risk of recurrence
in future offspring. Preimplantation genetic testing (PGT) can analyze embryos before
their transfer to the uterus and prevent the transmission of hereditary conditions to descendants,
however this procedure is of limited value in mtDNA conditions.
Methods: The list of diseases currently approved for PGT were reviewed. The process for eligibility,
was as for the Comissão Nacional Procriação Medicamente Assistida (CNPMA), of
Portugal (PT). Review of international practices for Assisted Reproductive Techniques (ART)
in IEM was carried out.
Results: As of 07.2022, 23 IEM diseases associated with deleterious variants in nDNA were
approved for PGT in PT. Couples at risk for conditions not included in the list can solicit an
evaluation from an expert committee, after a medical genetics consultation. To qualify for approval,
diseases must cause significant suffering and/or premature death. Due to a greater number
of solicitations many more IEM conditions have been approved for PGT across the world.
ART for mtDNA is not available in PT. International expert centers include PGT for specific
well documented variants and mitochondrial donation.
Conclusion: PGT is a reliable approach to reduce the risk of transmission of a genetic condition
to the offspring. The list of IEM disorders currently accepted for this technique in Portugal are
small, but it is expanding, as many more diseases fit the necessary criteria. While appealing in
theory, low success rates coupled with limited availability can be discouraging for patients. Genetic
counselling is of paramount importance after the diagnosis of IEM diseases. It is important
for both clinicians and patients to be made aware of the available reproductive options and their
limitations.
