مقالات پذیرفته شده در نهمین کنگره بین المللی زیست پزشکی
Preimplantation Genetic Testing for PAH Mutations in Two Iranian Families: A Case Report
Preimplantation Genetic Testing for PAH Mutations in Two Iranian Families: A Case Report
Elham Ghadirkhomi,1,*Arezu Noruzi,2
1. Academic Center for Education, Culture, and Research (ACECR), Iran. 2. Academic Center for Education, Culture, and Research (ACECR), Iran.
Introduction: Introduction
Phenylketonuria (PKU) is a prevalent autosomal recessive metabolic disorder resulting from pathogenic variants in the phenylalanine hydroxylase (PAH) gene. The enzyme catalyzes the hydroxylation of phenylalanine to tyrosine, a reaction requiring tetrahydrobiopterin (BH4) as a cofactor. Deficiency of PAH leads to accumulation of phenylalanine and its neurotoxic derivatives, along with insufficient tyrosine production and subsequent impairment of neurotransmitter synthesis. Clinically, untreated PKU causes severe neurocognitive dysfunction, seizures, behavioral disturbances, and psychiatric complications. The global implementation of newborn screening has improved early detection and dietary management of PKU; however, in many regions including Iran, the disease remains a public health challenge. The prevalence is influenced by high rates of consanguinity, which increase the recurrence risk in affected families. Several studies have described a diverse mutational spectrum in Iranian cohorts, with splice-site variants such as c.1066–11G>A being particularly common. In such populations, preventive reproductive options are crucial. Preimplantation genetic testing for monogenic disorders (PGT-M) has emerged as a reliable approach, enabling genetic characterization of embryos created by in vitro fertilization (IVF) before uterine transfer. By allowing selection of unaffected embryos, PGT-M directly prevents the birth of affected children. This report presents the outcomes of PGT-M applied to two consanguineous Iranian families carrying PAH variants, highlighting clinical feasibility, challenges, and implications for reproductive practice.
Methods: Methods
Whole-exome sequencing (WES) was conducted for both couples to identify pathogenic PAH variants.
Family 1: The female partner (23 years) and male partner (33 years), first cousins, were confirmed as heterozygous carriers of c.1218A>G and c.1243G>A.
Family 2: The female partner (29 years) and male partner (36 years), cross-cousins, had previously terminated a PKU-affected pregnancy confirmed via amniocentesis. WES revealed both were heterozygous for splice-site mutation c.441+1G>A in intron 4 of PAH. Based on molecular findings, custom PGT-M assays were designed. IVF with intracytoplasmic sperm injection (ICSI) was performed, and embryos were cultured to the blastocyst stage. Trophectoderm biopsies (5–8 cells) were taken, and DNA underwent whole-genome amplification (WGA). Targeted sequencing and SNP haplotyping enabled classification of embryos as affected, carriers, or unaffected. Simultaneous PGT-A was performed to detect aneuploidies, with the goal of prioritizing euploid embryos for transfer. Clinical outcomes were assessed by β-hCG assays and ultrasonography in the first trimester.
Results: Results
In Family 1, six embryos were analyzed. The results included several carriers, multiple affected embryos, and one unaffected embryo. Despite transferring the unaffected embryo, pregnancy was not achieved. In Family 2, nine embryos were analyzed. Three were homozygous affected, four were carriers, one gave inconclusive results, and one was unaffected and euploid. Transfer of the unaffected embryo resulted in a successful pregnancy, with normal findings confirmed during first-trimester follow-up.
Conclusion: Discussion and Conclusion
The findings illustrate both the potential and the limitations of PGT-M in consanguineous couples at risk of PKU. For Family 1, the procedure identified a transferable unaffected embryo, but pregnancy was unsuccessful, emphasizing that IVF outcomes are influenced by numerous factors beyond genetic status, including embryo quality, maternal factors, and procedural variables. By contrast, Family 2 achieved a successful pregnancy with a genetically unaffected embryo, demonstrating the clinical promise of this approach.
An additional consideration in reproductive genetics is the management of carrier embryos. In autosomal recessive diseases such as PKU, carriers are clinically unaffected, as demonstrated by both parents in these families. From a medical standpoint, transferring a carrier embryo is safe and does not cause disease in the offspring. However, decision-making is shaped by ethical, cultural, and personal factors. Some couples may accept carriers as an appropriate choice, particularly when the number of embryos is limited, while others may prefer to transfer only completely unaffected embryos to avoid perpetuating pathogenic alleles. The optimal strategy requires individualized genetic counseling that addresses both medical facts and family preferences.
Although therapeutic innovations such as BH4 supplementation for responsive genotypes, enzyme substitution with pegvaliase, and experimental gene therapy approaches are expanding treatment horizons, none can eliminate the risk of transmission. PGT-M remains the only preventive strategy that ensures affected offspring are not conceived.
In conclusion, PGT-M for PAH mutations is a practical and effective preventive option for couples at risk of PKU, particularly in settings of consanguinity. These two case reports demonstrate both the challenges and the successes of its application. By expanding reproductive genetics services and ensuring equitable access to counseling and testing, healthcare systems in high-risk regions can meaningfully reduce the recurrence of PKU and improve reproductive autonomy for families.