First Brazilian birth after Preimplantation Genetic Testing for Severe Methylmalonic Acidemia: preventing sudden infant death

Rafael Berteli Fontes; Cezar Antonio Fontes; Rita de Cássia Sousa-Polezzi; Rita de Cássia Fuga Berteli Fontes; Taccyanna Mikulski Ali; Ana Cerveró

JBRA Assist. Reprod. 2026;00(0):00-00
CASE REPORT
doi: 10.5935/1518-0557.20260031

First Brazilian birth after Preimplantation Genetic Testing for Severe Methylmalonic Acidemia: preventing sudden infant death

Rafael Berteli Fontes¹, Cezar Antonio Fontes¹, Rita de Cássia Sousa-Polezzi², Rita de Cássia Fuga Berteli Fontes³, Taccyanna Mikulski Ali⁴, Ana Cerveró⁵

¹Clinical Department, Centro de Reprodução Humana - Clínica Lavie, Franca, SP, Brazil
²Embryology Laboratory, Centro de Reprodução Humana - Clínica Lavie, Franca, SP, Brazil
³Neonatal Intensive Care Unit, São Joaquim Hospital e Maternidade Unimed, Franca, SP, Brazil
⁴IgenomixBrazil, São Paulo-SP, Brazil
⁵IgenomixSpain, Valencia, Spain

Received August 15, 2025
Accepted March 06, 2026

Corresponding author:
Rita de Cássia Sousa-Polezzi
Embryology Laboratory
Centro de Reprodução Humana - Clinica Lavie
Franca, SP, Brazil
E-mail: laboratorio@lavieclinica.com.br

CONFLICTS OF INTEREST
The present manuscript has no conflict of interests.

ABSTRACT
Methylmalonic acidemia (MMA) is a rare autosomal recessive metabolic disorder caused by pathogenic variants in the MMUT gene, often associated with severe neonatal manifestations and sudden unexpected death in infancy (SUDI). Preimplantation Genetic Testing for Monogenic Diseases (PGT-M) offers a valuable reproductive option for at-risk couples seeking to prevent transmission of such conditions. This represents the first Brazilian case of a healthy birth following combined PGT-M and PGT-A for MMA known. After the neonatal loss of their first child due to mut⁰-type MMA, a couple underwent genetic testing, which identified compound heterozygosity in MMUT: a maternal deletion (c.1196_1197del) and a paternal duplication (c.213_216dup). Haplotype construction used parental and proband DNA. Two IVF cycles yielded 13 blastocysts; of these, one embryo was diagnosed as being both euploid and unaffected, and two were euploid and heterozygous carriers. One of those embryos was selected for transfer, resulting in an uneventful pregnancy and the live birth of a healthy female infant. This single case highlights the clinical utility of PGT-M to prevent the recurrence of a severe inborn errors of metabolism and underscores the importance of early genetic counseling in couples with prior adverse neonatal outcomes.

Keywords: preimplantation genetic testing, PGT-M, methylmalonic acidemia, MMUT, monogenic disease, assisted reproduction

INTRODUCTION

Inborn errors of metabolism (IEMs) are estimated to account for up to 6% of sudden unexpected deaths in infancy (SUDI) (Boles et al., 1998; Chace et al., 2001; Van Rijt et al., 2016). Among them, methylmalonic acidemia (MMA; MIM 251000) is a well-recognized cause of SUDI (Van Rijt et al., 2016). Clinically, MMA can manifest in the neonatal period with lethargy and metabolic crisis such as acidosis, hyperketonemia, hypoor hyperglycemia, and hyperammonemia-potentially progressing to multiorgan failure, coma, and death (Panigrahi et al., 2017; Manoli et al., 2022).
MMA is an autosomal recessive disorder caused by pathogenic variants in the MMUT gene, which encodes methylmalonyl-CoA mutase. This enzyme plays a key role in propionate metabolism by converting methylmalonyl-CoA into succinyl-CoA (Raval et al., 2015; Manoli et al., 2022). The severity of MMA correlates with residual enzyme activity. Individuals with the mut⁰ subtype, characterized by absent or minimal enzyme activity, typically present with severe phenotypes and poor prognosis. In contrast, those with partial deficiency (mut⁻) often exhibit milder symptoms and improved survival (Raval et al., 2015; Manoli et al., 2022). The disorder is rare, with most studies reporting a birth prevalence below 1 per 100,000 live births (Almási et al., 2019). However, data on MMA prevalence and genetic diagnosis in the Brazilian pediatric population remain scarce (Colombiano et al., 2020).
In Brazil, MMA is not completely included in the newborn screening program. Despite the promulgation of Law No. 14.154/2021, which expands the national newborn screening program, the effective implementation of this policy remains incomplete and uneven across states. As a result, disorders such as MMA are still not routinely screened in most regions, leaving a significant gap in early detection and prevention of SUDI cases. Conversely, early identification through newborn screening has been associated with reduced mortality, milder disease presentation, and improved neurodevelopmental outcomes (Manoli et al. 2022).
Preimplantation Genetic Testing (PGT), applied in the context of in vitro fertilization (IVF), allows couples at risk of transmitting genetic disorders to select unaffected embryos. Initially reported for MMA in 2015 (Bautista-Llácer et al., 2015), Preimplantation Genetic Testing for Monogenic Diseases (PGT-M) has since been successfully used in families with newly identified MMUT variants (Habibzadeh et al., 2020; He et al., 2022). This approach offers an alternative to prenatal diagnosis and plays a pivotal role in reproductive planning for families affected by monogenic disorders (Parikh et al., 2023).
In this study, we describe the case of a young couple who lost their first child during the neonatal period due to MMA. Following this experience, they sought assisted reproduction with the goal of preventing the recurrence of an IEM.

CASE DESCRIPTION

Clinical history and presentation
IRB/CEP approval was waived as this study is a case report. Written informed consent was obtained from the patient prior to the procedure, allowing the anonymous use of their clinical data for scientific research. The consent process followed institutional guidelines and was conducted in compliance with Brazilian Health Regulatory Agency (ANVISA) requirements. A male infant was born at term by cesarean section on June 6, 2023. At birth, he exhibited poor sucking and was supplemented with formula. By day 3 of life, he developed grunting and hypotonia, requiring admission to the neonatal intensive care unit (NICU). Initial laboratory findings revealed severe dehydration, metabolic acidosis, electrolyte disturbances, and renal dysfunction. Clinical deterioration included seizures, apnea, pancytopenia, and the need for mechanical ventilation and peritoneal dialysis.
Metabolic workup revealed markedly elevated levels of methylmalonic acid and homocysteine, raising suspicion for MMA. Despite the initiation of hydroxycobalamin therapy and metabolic support, the patient’s condition worsened. He developed refractory shock and disseminated intravascular coagulation (DIC), ultimately succumbing to intractable metabolic acidosis on June 18, 2023, at 13 days of life.
Postmortem molecular analysis identified a mut⁰ form of MMA due to compound heterozygosity in the MMUT gene (OMIM #251000). The maternal allele harbored a deletion, MMUT (NM_000255.4): c.1196_1197del [p.(Val399GlufsTer24)], while the paternal allele carried a duplication, c.213_216dup [p.Tyr73Leufs*12]. These frameshift variants are associated with complete enzyme deficiency and non-responsiveness to vitamin B12 therapy.

Genetic counseling and fertility assessment
Following genetic counseling, the couple underwent carrier testing that confirmed heterozygous status for each pathogenic variant. They were counseled regarding reproductive risks and informed about PGT-M as one of the strategies for family planning. Subsequently, the couple opted for it in association with IVF at a specialized laboratory. Parental DNA samples were collected to perform the PGT-M work up at Igenomix Spain. The PGT-M protocol included a combined direct and indirect approach using fluorescent PCR technology. The direct analysis involved PCR amplification and sequencing of the MMUT gene. Indirect analysis included amplification of informative short tandem repeat (STR) markers linked to MMUT: D6S1689, D6S1566, D6S951, D6S269, D6S49864, D6S948, and D6S272. PCR products were analyzed via capillary electrophoresis using the AB 3130 platform (Thermo Fisher Scientific, USA), allowing precise haplotype determination for embryo selection.

Preimplantation Genetic Testing for MMUT-Related Methylmalonic Acidemia: IVF procedures
The woman, a 29-year-old patient, underwent two cycles of IVF using a controlled ovarian hyperstimulation (COH) protocol with a GnRH antagonist regimen. Ovarian stimulation was achieved with recombinant follicle-stimulating hormone (rFSH) and human menopausal gonadotropin (hMG), followed by oocyte maturation triggered with recombinant human chorionic gonadotropin (rHCG). Oocyte retrieval occurred 35 hours after rHCG administration under transvaginal ultrasound guidance. The husband’s semen analysis revealed parameters within normal reference ranges. Fertilization was performed via intracytoplasmic sperm injection (ICSI). In the first IVF cycle, 10 mature oocytes were retrieved and fertilized, resulting in 9 fertilized oocytes, 6 of which progressed to day 5 blastocysts and were cryopreserved. In the second cycle, 11 mature oocytes were retrieved and fertilized, yielding 7 blastocysts. A total of 13 blastocysts-comprising fresh and previously cryopreserved embryos-were subjected to trophectoderm (TE) biopsy for PGT-M. Genomic DNA from biopsied TE cells was first subjected to whole genome amplification (WGA) using the Ion ReproSeq Kit (Thermo Fisher Scientific, USA). Both directwand indirect approaches were employed to analyze the mutations in each embryo, enabling the detection of parental mutations and informative linked polymorphic markers. A separate DNA aliquot was reserved for Preimplantation Genetic Testing for Aneuploidies (PGT-A), performed at the Igenomix Brazil laboratory using next-generation sequencing (NGS) technology, following the validated protocol described by García-Pascual et al. (2020). Sequencing was carried out on the Ion S5 System (Thermo Fisher Scientific, USA), and data were processed through Ion Reporter software, aligned to the hg19 human reference genome. Combined PGT-M and PGT-A results for nine embryos are presented in Table 1. Four embryos exhibited amplification failure during preimplantation genetic testing, indicating that the DNA could not be reliably amplified to generate conclusive results, and were therefore excluded from further consideration.

Table 1. PGT-M, PGT-A, and embryo morphology.

Embryo transfer and outcomes
Genetic analysis of 9 blastocysts identified four embryos as affected, carrying both pathogenic MMUT variants. Two embryos were genetically unaffected (non-carriers) but demonstrated aneuploid or chaotic chromosomal profiles on PGT-A. Among the remaining embryos, one was identified as a non-carrier with a euploid karyotype, and two were heterozygous carriers (single pathogenic MMUT variant) with euploid chromosomal profiles.
Following compreHensive genetic counseling and informed consent, the couple elected to proceed with the transfer of a single euploid heterozygous carrier embryo - Figure 1. Endometrial preparation for Frozen Embryo Transfer (FET) was followed a hormone replacement protocol, consisting of oral estradiol (8 mg/day) initiated on day 3 of the menstrual cycle. After 12 days of estradiol administration, the endometrium measured 9 mm in thickness, and vaginal micronized progesterone (600 mg/day) was initiated to support implantation.

Figure 1. Embryo images at FET showing blastocyst re-expansion, approximately two hours later, after thawing.

The embryo transfer resulted in a positive serum β-hCG level of 123.4 mIU/mL, measured 10 days post-transfer. The pregnancy progressed without complications. First-trimester ultrasound at 12 weeks and 4 days of gestation demonstrated normal fetal biometry (CRL: 5.26 cm), fetal heart rate of 161 bpm, presence of the nasal bone, and nuchal translucency measurement of 1.41 mm, all within the expected reference ranges for gestational age - Figure 2. The pregnancy culminated in the live birth of a healthy female infant.

Figure 2. First-trimester obstetric ultrasound at 12 weeks and 4 days, showing crown-rump length (CRL: 5.26cm), nuchal translucency (NT: 1,41 mm), nasal bone and fetal heart rate (HR), within normal range. The images display biometric parameters and ultrasonographic markers used in first-trimester aneuploidy screening.

DISCUSSION

PGT-M has seen significant growth in both complexity and frequency (ASRM, 2023). Data from the European Society of Human Reproduction and Embryology (ESHRE) Preimplantation Genetic Diagnosis Consortium indicates a steady annual increase in IVF/PGT-M cycles (Coonen et al., 2020). According to recent analyses, nearly two-thirds of PGT-M procedures target autosomal dominant diseases (64%), followed by autosomal recessive (19%) and X-linked disorders (18%) (Spinella et al., 2023). In contrast, data from Brazil show that recessive conditions can account for up to 40% of PGT-M indications, reflecting population-specific genetic backgrounds and screening practices.
MMA is a severe autosomal recessive disorder with high morbidity and mortality, particularly in early-onset forms. Even with treatment, affected individuals remain at risk for intellectual disability, kidney failure, and recurrent metabolic crises, which may progress to coma or death. Mortality rates in the early 2000s were estimated at approximately 40% (Zhou et al., 2018), underscoring the urgency of early diagnosis and the rationale for incorporating PGT-M into reproductive planning when biallelic pathogenic variants are identified.
Despite its clinical severity and early onset, methylmalonic acidemia (MMA) is not currently included in the Brazilian national newborn screening program. Although Law No. 14.154/2021 expanded the scope of neonatal screening, the effective implementation of this policy remains incomplete and uneven across different states (Randon et al., 2020; Manoli et al., 2022). Its detection is limited to expanded carrier panels available in private settings, a gap that highlights the need to broaden access to genetic screening and counseling-especially in families with a history of early neonatal loss or suspected metabolic disorders. Current guidance documents do not specify which conditions should be included on an expanded panel, but there is consensus among professional societies that expanded carrier screening panels should focus on childhood-onset conditions likely to have a significant impact on quality of life.
Once causative mutations are established in a proband, at-risk couples can be offered carrier screening and reproductive options such as prenatal or preimplantation genetic testing (Manoli et al., 2022). Based on Mendelian inheritance, approximately 50-75% of embryos in PGT-M for recessive disorders are expected to be unaffected (either carriers or wild-type) (Harper et al., 2012). Internal data from Igenomix suggest that, on average, six embryos are needed to achieve an 85% chance of obtaining at least one transferable embryo (Igenomix internal data).
Over 250 pathogenic variants in the MMUT gene have been identified (Acquaviva et al., 2005; Worgan et al., 2006). While some founder mutations have been reported in specific populations, no single predominant pathogenic variant has been identified in the genetically diverse American population (Ledley et al., 1988). This molecular heterogeneity adds another layer of complexity to PGT-M test development for MMA, since the test cannot predict the embryo´s phenotype.
Despite technological advances and an increasing number of cases, PGT-M remains a complex process that requires individualized genetic counseling, prior confirmation of parental variants, and case-specific assay development-ideally completed before the initiation of IVF. Technical and interpretive challenges persist, including the need for assay customization and the nuanced classification of embryos. Therefore, establishing realistic expectations through transparent communication about test limitations and alternative reproductive options is essential early in the process (ASRM, 2023).
Also, comparative studies indicate that about half of PGT-M-unaffected embryos may still be aneuploid (mean maternal age 32.4 years). Combining PGT-M with Preimplantation Genetic Testing for Aneuploidies (PGT-A) can improve implantation rates (75% vs. 53%) and live-birth rates (59.4% vs. 37.5%), while reducing miscarriage (20% vs. 40%). However, it also decreases the number of embryos available for transfer (Goldman et al., 2016). Although the risk of aneuploidy in younger women is not negligible-studies report that embryonic aneuploidy among women aged 26-30 years ranges from 20% to 27% (Franasiak et al., 2014)-current evidence suggests that the overall benefit of PGT-A may be limited in this group (Scriven, 2022). Most aneuploidies arise from maternal meiotic errors, but growing evidence indicates that paternal factors may also contribute to embryonic aneuploidy and infertility outcomes (Rodrigo et al., 2019). Importantly, some viable embryos may be discarded due to mosaicism or false-positive aneuploidy results (Scriven, 2022; Calull et al., 2025). In one retrospective NGS study, 17.1% of embryos with reproductive potential would have been excluded if PGT-A had been applied prior to transfer (Shen et al., 2022). Therefore, the use of PGT-A alongside PGT-M should be individualized, carefully balancing potential benefits against the risk of discarding embryos capable of producing healthy live births.
Beyond technical considerations, emotional and ethical factors are central to reproductive decision-making. Parents of children with chronic or life-limiting conditions frequently report profound emotional strain associated with witnessing their child’s suffering (Pergament, 1991; Hui et al., 2002; Roberts & Franklin, 2004; Kalfoglou et al., 2005), particularly because for most genetic disorders, management is limited to alleviating symptoms with no curative treatments currently available (Gallois et al., 2025).

CONCLUSION

This single case illustrates the successful use of PGT-M in preventing the recurrence of a severe and life-threatening form of methylmalonic acidemia (MMA) in a young Brazilian couple following neonatal loss. The identification of compound heterozygous variants in the MMUT gene and the application of individualized genetic testing strategies enabled the birth of a healthy child, highlighting the value of PGT-M even in younger patients, where genetic risk may often be underestimated.
Importantly, this case underscores a critical gap in the Brazilian healthcare context: current newborn screening programs in Brazil do not routinely include MMA, a rare but potentially fatal metabolic disorder. This highlights the need for broader access to carrier screening and genetic counseling in the preconception period, particularly for families with a history of early infant loss, to allow timely diagnosis and expand reproductive options for at-risk couples.
As genetic technologies continue to evolve, their integration into routine clinical care in Brazil represents a powerful tool for preventing devastating inherited diseases.

ACKNOWLEDGEMENTS

The authors would like to thank the parents for allowing the study to be conducted.

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