Hong Kong PGT (Third-Generation IVF) – Detailed Explanation of Screenable Genetic Diseases and Technical Limitations

========== Opening: Direct Answer ==========

Direct Answer: Hong Kong's third-generation IVF technology (Preimplantation Genetic Testing, PGT) can screen for diseases clearly divided into three categories: chromosomal aneuploidies (e.g., Trisomy 21, Trisomy 18, Trisomy 13), chromosomal structural abnormalities (balanced translocations, Robertsonian translocations, inversions, etc.), and monogenic diseases (thalassemia, spinal muscular atrophy, hereditary deafness, cystic fibrosis, hemophilia, and over 200 others). However, PGT cannot screen for polygenic diseases (e.g., diabetes, hypertension) or non-genetic birth defects, and detection accuracy is limited by the technical platform and embryo cell sampling.

========== A: Direct Answer to the Question ==========

1. What diseases can Hong Kong third-generation IVF specifically screen for?

Hong Kong third-generation IVF corresponds medically to three technical pathways, each covering different types of genetic abnormalities:

It should be clarified that the number of monogenic diseases detectable by PGT-M depends on the testing panel established by the fertility center. Institutions such as Hong Kong Sanatorium & Hospital, Union Hospital, and the Hong Kong Reproductive Medicine Centre typically cover 100–300 monogenic diseases with known pathogenic genes, but not all genetic diseases can be tested — only those with clearly identified pathogenic genes and included in the testing panel.

========== B: Why does this issue arise? ==========

2. Why can't PGT screen for all diseases?

This is one of the most common misconceptions in clinical practice. The core limitations of PGT technology are reflected in three aspects:

• Clarity of Genetic Etiology: Only diseases with known pathogenic genes and mutation sites can have detection probes designed. Diseases caused by multiple genes combined with environmental factors, such as hypertension, diabetes, and schizophrenia, cannot be predicted by PGT.
• Limitations of Embryo Cell Sampling: PGT extracts DNA from 3–5 trophectoderm cells of the blastocyst for testing, which may not fully represent all cells of the embryo (possibility of mosaicism).
• Differences in Technical Platforms: Different testing platforms (NGS, aCGH, SNP array) vary in resolution and detection range. For example, NGS platforms can simultaneously detect aneuploidies and some monogenic diseases, but have limited sensitivity for detecting small fragment deletions/duplications.

========== C: What do doctors think? ==========

3. Consensus among reproductive doctors on the scope of PGT screening

According to clinical guidelines from the Hong Kong Association of Reproductive Medicine (HKASRM) and various fertility centers, doctors emphasize the following logic when assessing whether a patient is suitable for PGT:

• When is it suitable: Female age ≥38 years, recurrent miscarriage ≥2 times, repeated implantation failure ≥3 times, known carrier of chromosomal abnormality, carrier or patient of a monogenic disease, advanced paternal age (≥45 years), etc.
• When is it unsuitable: Undergoing PGT solely for "gender selection" (Hong Kong law prohibits non-medical sex selection); advanced age with very low ovarian reserve and inability to obtain sufficient blastocysts for biopsy; polygenic or non-genetic diseases.

Doctors clearly state that PGT can reduce but cannot eliminate genetic risk. For example, PGT-A can reduce the miscarriage rate due to chromosomal aneuploidy from 40–50% to 10–15%, but cannot completely prevent miscarriage.

========== D: Differences across age groups ==========

4. Differences in screening needs among women of different ages

In clinical practice, a common misconception among advanced-age women is that "doing PGT guarantees a healthy baby." In reality, PGT-A can only screen for chromosomal aneuploidies, cannot detect embryo morphology, developmental potential, or monogenic diseases, and has a false positive and false negative rate of approximately 2–5%.

========== E: Differences between countries ==========

5. Differences in PGT screening scope between Hong Kong, Mainland China, and overseas

Regulatory policies and technology access in different regions directly affect the range of screenable diseases:

• Hong Kong: PGT-A, PGT-M, and PGT-SR are all legally available, and simultaneous HLA matching testing (for "savior siblings") is permitted. Monogenic disease testing panels require approval from the Hong Kong Department of Health, covering approximately 200–300 diseases.
• Mainland China: PGT (third-generation IVF) requires clear medical indications and is strictly regulated by the "Administrative Measures on Human Assisted Reproductive Technology." Monogenic disease testing must be conducted at approved centers; the range of detectable diseases is similar to Hong Kong, but the approval process is more complex.
• USA/Thailand: PGT technology is more widely applied. Some laboratories offer more comprehensive gene testing panels (e.g., covering 400+ monogenic diseases), but regulation is relatively relaxed. Attention should be paid to differences in laboratory qualifications and quality control standards.

The advantages of choosing Hong Kong for PGT include: clear legal framework, testing standards aligned with international practices, a well-established genetic counseling system, and lower language and cultural communication costs for patients from Mainland China.

========== G: Most easily overlooked details ==========

6. Three most easily overlooked details

6.1 Risk of missing mosaic embryos

PGT biopsy only takes 3–5 trophectoderm cells. If the embryo has mosaicism (some cells chromosomally normal, some abnormal), the biopsied cells might coincidentally be normal, leading to a "false negative." The higher the mosaicism ratio, the greater the risk of missed detection. Hong Kong fertility centers usually indicate "possible mosaicism" in the report and recommend prenatal diagnosis (amniocentesis) for verification after transfer.

6.2 Resolution limitations of testing platforms

Different NGS platforms have varying detection sensitivity for small fragment deletions/duplications (<1Mb). If one partner carries a microdeletion (e.g., 22q11.2 microdeletion syndrome), it is necessary to confirm whether the laboratory platform can effectively detect it. It is recommended to request the platform performance parameters from the center before testing.

6.3 PGT-M requires a proband gene report

This is the most easily overlooked prerequisite. Before proceeding with PGT-M, a genetic diagnosis report of the affected family member (proband) or confirmed carrier reports from both partners must be provided. Families without a clearly identified pathogenic gene locus cannot initiate the PGT-M process.

========== H: Common pitfalls ==========

7. Four common cognitive misconceptions

• Misconception 1: "PGT can screen for all genetic diseases." — In reality, it can only screen for diseases with clearly known pathogenic genes and is limited by the testing panel.
• Misconception 2: "If I do PGT, the embryo will definitely not miscarry." — PGT-A can reduce the miscarriage rate by about 60%, but cannot completely prevent it; there is still a 10–15% miscarriage risk (mainly from factors other than aneuploidy).
• Misconception 3: "PGT can replace prenatal diagnosis." — PGT is a pre-implantation screening and cannot replace amniocentesis or chorionic villus sampling during pregnancy. All PGT pregnancies are recommended to undergo prenatal diagnosis for confirmation.
• Misconception 4: "All Hong Kong fertility centers have the same PGT testing scope." — Testing panels, technical platforms, and quality control standards vary between centers. Before choosing, request the center to provide a list of detectable diseases and testing performance data.

========== Q: Frequently asked questions ==========

8. Frequently asked questions

8.1 Can Hong Kong third-generation IVF screen for thalassemia?

Yes. α- and β-thalassemia are among the most common indications for PGT-M in Hong Kong. The specific mutation types of both partners (e.g., --SEA/αα, IVS-Ⅱ-654) must first be confirmed, and the laboratory designs detection probes accordingly. Note: Silent thalassemia carriers (e.g., -α/αα) are usually not included in the PGT-M scope, as it has minimal impact on health.

8.2 Can it screen for spinal muscular atrophy (SMA)?

Yes. SMA (SMN1 gene deletion/mutation) is included in Hong Kong PGT-M testing panels and is suitable for families where both partners are carriers. Approximately 1 in 50 people in Hong Kong are SMA carriers. PGT-M can select embryos carrying a normal SMN1 gene.

8.3 Can it screen for hereditary deafness?

Yes. Mutations in GJB2 (causing autosomal recessive deafness), SLC26A4 (causing Pendred syndrome), and others can be detected. However, note that deafness has high genetic heterogeneity; testing only covers known pathogenic sites, and a negative result cannot rule out other hereditary deafness possibilities.

8.4 What chromosomal abnormalities can PGT-A detect?

PGT-A can detect aneuploidies for all 24 chromosomes (22 pairs of autosomes + X + Y), including gains or losses of entire chromosomes, as well as partial deletions/duplications >5Mb. Common detectable abnormalities include: Trisomy 21, Trisomy 18, Trisomy 13, 45,X, 47,XXY, 47,XYY, 47,XXX, and mosaic forms.

8.5 What materials are needed for PGT?

• Karyotype analysis report for both partners (valid within 1 year)
• Genetic disease diagnosis report (for PGT-M, requires proband report or carrier reports from both partners)
• Previous reproductive history records (miscarriage, termination, malformed children, etc.)
• Registration materials required by the fertility center (identity proof, marriage certificate, medical indication records, etc.)

========== Closing: Risk reminder ==========

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