Spinal Muscular Atrophy Thailand IVF Screening | PGT‑M SMA Genetic Blocking Conditions & Process

Opening: Real consultation scenario

A 32-year-old woman sat down in the genetic counseling clinic and handed over a report: "My husband's brother passed away from spinal muscular atrophy. My husband himself is a carrier of a heterozygous deletion in the SMN1 gene. We are planning to have a child. After researching a lot, we read that embryo screening is available in Thailand. We want to confirm whether SMA can actually be screened? What is the specific procedure?" This question is not uncommon in genetic counseling. Spinal Muscular Atrophy (SMA) is an autosomal recessive genetic disorder. For couples with a family history of SMA or where both partners are carriers, using preimplantation genetic testing for monogenic diseases (PGT‑M) to block inheritance is a feasible technical path. However, whether screening is possible, where it can be done, and what prerequisites exist need to be examined separately.

1. Direct Answer: Can SMA be screened via Thailand IVF?

Yes, it can be screened, but with strict prerequisites. Some reproductive centers in Thailand with the capability for monogenic disease testing can perform preimplantation genetic testing (PGT‑M) for spinal muscular atrophy on embryos. The testing targets deletions or point mutations in the SMN1 gene, using NGS sequencing combined with SNP haplotype analysis to select embryos that do not carry the pathogenic gene for transfer. However, the following four basic conditions must be met:

• Both partners or at least one partner has a clearly identified pathogenic mutation site (SMN1 deletion or mutation type) through genetic testing;
• Sufficient embryos are available for testing (at least 5–6 blastocysts for biopsy and screening);
• The collaborating genetic laboratory has qualifications for monogenic disease testing and experience with SMA testing;
• Genetic counseling has been completed and informed consent signed, with an understanding of the limitations and residual risks of the testing.

2. A Reproductive Geneticist's Perspective on SMA Embryo Screening

Spinal muscular atrophy is an autosomal recessive genetic disorder, with the pathogenic gene SMN1 located on chromosome 5. The carrier rate in the general population is approximately 1/40 to 1/50. When both partners are carriers, there is a 25% chance that their offspring will be affected. For couples who have already had a child with SMA or where both are carriers, the need to have a healthy child is urgent.

The core logic of PGT‑M technology is: before embryo implantation, 3–5 trophectoderm cells are biopsied to test whether the embryo carries the pathogenic gene. For SMA, the testing strategy usually involves two steps:

• Direct testing: Using NGS or MLPA technology to detect deletions in exon 7 of the SMN1 gene (responsible for >95% of cases);
• Indirect linkage analysis: Using SNP haplotypes to track the pathogenic chromosome within the family, reducing the risk of misdiagnosis due to genetic recombination.

When both methods are combined, the accuracy rate can reach 95%–99%. However, it is important to note that approximately 2%–5% of SMA cases are caused by SMN1 point mutations or other complex rearrangements, requiring customized testing protocols. Therefore, genetic testing of both partners must be completed first, and if possible, samples from the proband (affected child) should also be included to design reliable testing probes.

3. Comparison of SMA Screening Differences: Thailand vs. USA vs. Mainland China

People choose Thailand for SMA embryo screening mainly due to its technical maturity and relatively flexible procedures. However, there are significant differences between countries in terms of regulations, technology, costs, and waiting times.

Note: The table above is a general reference. Actual costs and timelines vary significantly based on individual circumstances, laboratory choice, medication protocols, etc. Thailand's advantage lies in its relatively faster process and no need for lengthy approval waiting times, but it requires patients to assess laboratory qualifications themselves, posing a higher risk of information asymmetry.

4. Five Most Easily Overlooked Details

• Family Sample Requirements: Some laboratories require DNA samples from the proband (affected child) or both parents to construct haplotypes. Providing only samples from the couple may be insufficient for linkage analysis. Confirm the laboratory's requirements for sample type and source in advance.
• Impact of SMN2 Copy Number: SMN2 is a modifier gene; its copy number influences the severity of SMA but does not change pathogenicity. PGT‑M primarily determines whether the embryo carries a pathogenic SMN1 gene, but some laboratories may also report SMN2 copy numbers for reference. Clarify the scope of testing.
• Timing Window for Probe Design: Probe design must be completed before starting the IVF cycle. Otherwise, embryos may be waiting while the testing protocol is not ready, requiring embryo freezing. It is recommended to complete genetic testing and probe design first, then initiate ovarian stimulation.
• Embryo Biopsy Requirements for Blastocyst Quality: PGT‑M requires biopsy at the blastocyst stage on day 5/6. At least 3–5 good-quality blastocysts are needed for a reasonable chance of successful screening. Women with diminished ovarian reserve (AMH < 1.0 ng/mL) or advanced age (>38 years) may not produce enough embryos and should be evaluated in advance.
• Residual Risk and Prenatal Diagnosis: The accuracy of PGT‑M is not 100%. Due to genetic recombination, allele dropout (ADO), and other factors, there is a 1%–3% risk of misdiagnosis. After transfer, prenatal diagnosis (amniocentesis) is mandatory to confirm the fetal genotype. This step cannot be omitted.

5. Actual Process: From Genetic Counseling to Embryo Transfer

The overall process for SMA embryo screening in Thailand is divided into the following six stages:

1. Genetic Counseling and Family Genetic Testing: Both partners undergo blood tests for SMN1 gene deletion/mutation detection, including samples from the affected child or parents if necessary. After identifying the pathogenic site, a genetic counselor assesses the feasibility of PGT‑M.
2. Testing Protocol Design and Validation: The laboratory designs probes (NGS probes or SNP panels) based on the family genetic information, typically taking 4–8 weeks. Some laboratories perform pre-validation using the couple's DNA to confirm the protocol's effectiveness.
3. Entering the IVF Cycle: The woman undergoes ovarian stimulation (about 10–14 days), followed by egg retrieval. Eggs are fertilized with the partner's sperm to create embryos, which are cultured to the blastocyst stage on day 5/6.
4. Embryo Biopsy and Freezing: For blastocysts meeting biopsy criteria, 3–5 trophectoderm cells are removed, and the embryos are then cryopreserved. The biopsy samples are sent to the genetic laboratory for testing.
5. Genetic Testing and Result Analysis: The laboratory performs NGS sequencing and haplotype analysis on the biopsied cells to determine whether each embryo carries the SMN1 pathogenic mutation. Results typically take 2–4 weeks.
6. Selecting Embryos for Transfer: Based on the results, embryos not carrying the pathogenic gene are selected for frozen embryo transfer. Pregnancy is confirmed 12–14 days after transfer. Once pregnancy is established, amniocentesis for prenatal diagnosis is required at 16–18 weeks of gestation.

6. Timeline: How Long from Start to Transfer

The approximate timeline for the entire process is as follows:

Total Duration: From the first genetic counseling session to completing the transfer, under favorable conditions, it takes approximately 4–6 months. If probe design takes longer or if insufficient embryos require a new egg retrieval cycle, the timeline may extend to 7–9 months. It is recommended to plan for at least 6 months.

7. Special Situations: Complex Rearrangements and De Novo Mutations

Genetic testing for SMA is not always straightforward. The following situations require special handling:

• High Homology Between SMN1 and SMN2: The two genes share 99% sequence similarity, making it difficult for standard sequencing to distinguish them. Long-range PCR or MLPA techniques are needed for differentiation, along with SNP haplotypes for family linkage analysis.
• De Novo Mutations: If there is no family history of SMA but a fetus is diagnosed with SMA, it is necessary to verify whether the parents are carriers. If neither parent is a carrier, it may be a de novo mutation. In this case, PGT‑M requires customized testing for the mutation site and confirmation of the mutation's origin.
• One Partner Has SMA, the Other Is a Carrier: The affected individual carries two pathogenic SMN1 alleles (homozygous deletion or compound heterozygous). In this scenario, all embryos will carry at least one pathogenic allele. The goal is to select embryos with the mildest carrier status (e.g., carrying only one pathogenic allele and having a higher SMN2 copy number). However, this approach involves ethical considerations and requires thorough genetic counseling.
• Complex Recombination Events: In rare cases, the SMN1 gene undergoes conversion or rearrangement, making standard testing unable to accurately determine the status. Whole genome sequencing or customized SNP arrays may be required, significantly increasing cost and time.

In these complex situations, the experience of the laboratory and the judgment of the genetic counselor are crucial. Before selecting a laboratory in Thailand, it is advisable to request data on their success rates with similar cases.

8. Summary of Frequently Asked Questions