Identification of Fowler syndrome (hydrocephaly-hydranencephaly proliferative vasculopathy) in a pregnancy following single euploid embryo transfer

Abstract

Background

Genetic carrier screening is a useful tool for couples looking to understand the genetic risk profile of their offspring. However, this method is limited in identifying rare genetic variants.

Case

A couple undergoing single euploid embryo transfer (SEET) following planned embryo banking was followed in this study. The patient was a 39-year-old nulliparous female with negative expanded carrier screening (ECS) which included 400 autosomal recessive and X-linked conditions. Her partner was a 39-year-old male with no pertinent past medical history. Clinical pregnancy was achieved following SEET. Unfortunately, the fetus demonstrated a constellation of neurologic malformations at 28 weeks gestation and the couple opted for termination. Amniocentesis was conducted at the time of labor induction revealing unremarkable chromosome analysis and microarray testing. Whole genome sequencing (WGS) noted paternal and maternal variants of the fetal leukemia virus subgroup C cellular receptor family, member 2 protein (FLVCR2). The paternal variant was classified as pathogenic, and the maternal variant was classified as a variant of uncertain significance by the lab. The presence of balletic FLVCR2 variants in the setting of neurologic anomalies was consistent with Fowler syndrome, a rare autosomal recessive condition.

Conclusion

This case highlights the inherent limitations of carrier screening in detecting rare genetic disease and marks the first documented case of Fowler syndrome following single euploid embryo transfer.

Background

Fowler Syndrome is often a prenatal lethal condition characterized by cerebral malformations such as hydrocephaly-hydrancephaly, severe cortical atrophy, and glomeruloid vasculopathy. This is inherited in an autosomal recessive fashion and has also been referred to as proliferative vasculopathy and hydranencephaly-hydrocephaly (PVHH) and encephalic proliferative vasculopathy given its proclivity to destroy central nervous system (CNS) tissue through progressive vasculopathy [1–5]. The disease was first described in a 1972 report outlining the potential association of central nervous system vasculopathy and enlarged cerebral hemispheres in five fetuses from a single family [6]. Since then, 72 total cases of Fowler syndrome have been described in the literature, many of which have stemmed from the same families [7].

Feline leukemia virus subgroup C cellular receptor family, member 2 protein (FLVCR2) is a cell surface transmembrane protein largely involved with heme transport and calcium metabolism [8, 9]. While this protein is widely expressed in the human liver, placenta, and kidney, it is ubiquitous in the brain and spinal cord [8]. Heme’s integral role in mediating oxidative phosphorylation, which is necessary for neuronal migration, suggests that impairment in heme transport impairs neuronal function. Dysfunctional heme transport could promote neurodegeneration and CNS anomalies such as those observed in Fowler syndrome [10]. Radio et al. supported this hypothesis by documenting FLVCR2 misfolding in association with a p.Ser203Tyr amino acid change [11]. Additionally, dysfunctional calcium metabolism has been implicated in the pathogenesis of Fowler syndrome as evidenced by calcified glomeruloid deposits on histology and destabilization during CNS remodeling [12, 13].

Fowler syndrome abnormalities are primarily observed on prenatal ultrasounds and have been identified as early as 12 weeks of gestation. Hallmark sonographic findings include fetal hydrocephaly, polyhydramnios, pterygia, and akinesia [1]. This case report contributes to the limited clinical understanding of Fowler syndrome and highlights the potential role of whole genome sequencing (WGS) in improving detection and reducing the incidence of Fowler syndrome in the era of assisted reproductive technology (ART).

Case report

A 39-year-old nulliparous woman presented to a reproductive endocrinology and infertility (REI) specialist to discuss fertility testing and family building. The couple had been trying to conceive for about 4 months and, given the advanced age of the female partner in the setting of desiring two children, they preferred to be more aggressive with fertility treatment, ultimately deciding to pursue in vitro fertilization (IVF). The female partner had no pertinent past medical history other than subclinical hypothyroidism incidentally identified during the infertility workup. Her partner’s past medical history was unremarkable. Expanded carrier screening (ECS) was performed using the Beacon 427 (female) and Beacon 370 (male) panels. ECS was drawn only after the couple watched educational videos regarding the genetic screening modality and signed consent forms which included acknowledgement of residual risk. The female partner screened negative for all conditions tested and the male partner screened positive for two autosomal recessive (AR) conditions. The couple underwent one cycle of IVF, generating nine euploid embryos, then proceeding with a frozen embryo transfer (FET) of a single euploid embryo. The first FET did not result in implantation success. In turn, the couple proceeded with a second FET of a single euploid transfer, resulting in an ongoing pregnancy. The couple was discharged between 8 and 9 weeks of gestation to her prenatal provider where noninvasive prenatal testing (NIPT) and nuchal translucency (NT) were low risk.

At 28 weeks gestation, routine prenatal anatomy ultrasound identified mild ventriculomegaly. Follow-up fetal magnetic resonance imaging (MRI) demonstrated bilateral lateral ventriculomegaly, bilateral parenchymal thinning, susceptibility along the margins of the lateral ventricles, and multiple brain measurements that were small for gestational age. Given the poor prognosis associated with these findings, the couple elected to terminate this pregnancy through induction of labor. Intracardiac potassium chloride (KCl) injection was administered to the fetus to induce cardiac arrest prior to the induction process. Amniocentesis was conducted at the time of induction and demonstrated unremarkable chromosome analysis and microarray testing; however, whole genome sequencing (WGS) was notable for a paternally inherited pathogenic FLVCR2 variant and a maternally inherited FLVCR2 variant of uncertain significance. Biallelic pathogenic variants in the FLVCR2 gene have been associated with Fowler syndrome, which is characterized by proliferative vasculopathy, hydrocephalus, and brain malformations all consistent with the fetus’ phenotype on early ultrasound. Although the patient’s FLVCR2 variant was considered a VUS, the fetal phenotype strongly correlated, and therefore, the genetics team strongly suspected that the presence of these two alleles was implicated in the fetus’ anomalies.

Postpartum, the couple met with the genetic counselor and REI and their fertility clinic. The couple understood that while the VUS is strongly suspected to be disease-causing, it is possible that there is an alternative underlying cause that has not been identified. After discussion with the teams at the fertility clinic and the PGT lab, the couple moved forward with screening their seven remaining euploid embryos for these variants via preimplantation genetic testing for monogenic disorders (PGT-M). The embryos were thawed and re-biopsied for PGT-M. Two blastocyst embryos were found to be affected (i.e., compound heterozygous), three were found to be carriers (i.e., heterozygous), one blastocyst embryo was unaffected, and one blastocyst embryo resulted as indeterminate due to a recombination event.

Discussion

This case highlights the limitations of ECS in detecting a couple’s risk to have a child affected by rare genetic syndromes. ECS utilizes a predefined list of well-characterized conditions, such as cystic fibrosis and Tay–Sachs disease, and exclusively reports variants that are classified as pathogenic or likely pathogenic by the carrier screening laboratory. While this finite list allows ECS to efficiently examine patients’ carrier status for hundreds of genetic conditions, it is limited in identifying rare genetic variants [14]. For instance, Fowler syndrome was not included in the Beacon ECS utilized by this couple due to the condition’s rarity. In contrast, WGS analyzes an individual’s genome and reports variants of unknown significance (VUS). These variants have an uncertain effect on protein function and have not yet been confirmed to cause disease [15, 16]. VUS may be later updated to benign, likely benign, likely pathogenic, or pathogenic based on further review of population data, functional studies, or family tracing to search for a similar condition [17]. In the case presented, the clinical team’s ability to diagnose this rare condition was contingent upon the interpretation of the WGS result in the context of the observed fetal phenotype. Without the abnormal fetal ultrasound findings, the VUS would not have been suspected to cause disease. Early utilization of WGS to identify pathogenic variants or VUS has been suggested as an adjunct to ECS. However, WGS results often cannot be interpreted without supportive phenotypic findings. Additionally, WGS can bear a high financial cost. These factors argue against the universal use of WGS, unless otherwise indicated by a patient’s history [18].

The ongoing possibility of pregnancy abnormalities following negative ECS is referred to as residual risk. Etiologies underlying residual risk include incomplete mutation detection secondary to de novo mutations, technical challenges, or inaccurate variant curation [14]. The pathogenicity of a variant may not always be clear; one lab may classify a variant as pathogenic while another may categorize the same variant as a VUS. In addition, ECS cannot assess risk for chromosome-related or multifactorial conditions and does not account for a patient’s family history. A family history of a known genetic disease should be shared with a patient’s clinical team, and additional genetic testing should be considered when warranted. While discussion of residual risk is recommended prior to undergoing ECS, a survey by Ioannou et al. found that fewer than 25% of patients undergoing ECS were able to correctly answer questions related to residual risk [19]. This emphasizes the need to strengthen patient counseling on the limitations of ECS.

Ultimately, screening individuals for rare genetic conditions in a cost-effective fashion remains challenging for both patients and providers. While efficient, inexpensive methods such as carrier screening exist, negative screening results may provide false reassurance to couples who unknowingly have an increased reproductive risk for a rare genetic condition that was not identified on ECS. This resultant residual risk should be discussed with patients who utilize ECS in the preconception period to ensure they discuss prenatal screening options such as anatomy scans, non-invasive prenatal testing (NIPT), and/or diagnostic prenatal testing.

Conclusion

This case report of Fowler syndrome was detected in the setting of two people utilizing IVF with PGT-A after having preconception ECS. The couple’s clinical course highlights the limitations of ECS and the residual risk of rare diseases.

Author contribution

RD and AG conceived and designed research. VL wrote the manuscript. DW provided insight from a clinical genetics perspective. AC provided feedback on manuscript assembling and writing. All authors read and approved the manuscript.

Data availability

Patient health information discussed in this case report may be found in our institution’s electronic health record system. Data will be made available to the editors of the journal for review or query upon request.

Declarations

Ethical approval

Retrospective review of this case was approved by an academic Institutional Review Board (HS number STUDY-18–00441).

Competing interest

VL: none; AG: none; DW: none; JL: none; ABC: Progyny; RD: none.