Nongenetic risk factors for holoprosencephaly: An updated review of the epidemiologic literature

A male fetus with cyclopia was discovered after miscarriage: A rare case report from Syria

Key Clinical Message

This case of alobar holoprosencephaly and cyclopia emphasizes the value of prenatal check-ups, particularly in low-income countries. Early ultrasound diagnosis leads to early gestational termination, preventing psychological trauma for the parents.

Abstract

Alobar holoprosencephaly is a rare-occurrence malformation with a bad prognosis linked to cyclopia, the most severe cranial feature. Prenatal examinations are essential for identifying these deformities and preventing parental mental health damage.

Efficacy of Systematic Early-Second-Trimester Ultrasound Screening for Facial Anomalies: A Comparison between Prenatal Ultrasound and Postmortem Findings

Second-trimester 2D ultrasound (US) assessment of the fetal anatomy, as proposed by worldwide guidelines, allows detecting the majority of fetal malformation. However, the detection rates of fetal facial anomalies seem to still be low, mostly in cases of isolated facial malformation. The purpose of this research was to assess and analyze the concordance between the antenatal imaging findings from second-trimester US screening and the results of fetal postmortem autopsy. Between January 2010 and January 2020, there were 43 cases where fetuses with prenatal ultrasound diagnosis of a face abnormality, associated or not with a genetic syndrome or chromosomal disorder, following intrauterine death (IUD) or termination of pregnancy (TOP) after the 13 weeks of pregnancy, underwent autopsy in the Pathological Anatomy section of Bari Polyclinic specializing in feto-placental autopsies. The diagnosis of the fetal facial defects at ultrasound was compared with the findings at autopsy in all cases. A very high level of agreement between prenatal ultrasound and autopsy findings was found for facial abnormalities associated with genetic syndromes or numerical abnormality of chromosomes. A lower level of concordance was instead found in isolated facial defects or those associated with other organ anomalies, but not associated with genetic syndrome or numerical chromosome anomaly. A detailed examination of aborted fetuses led to successful quality control of early-second-trimester ultrasound detection of facial anomalies; however, it was less accurate for the isolated ones. It is, thus, reasonable to propose a systematic early-second-trimester prenatal ultrasound screening for facial anatomy by operators specialized in fetal medicine field, using 2D, 3D, and 4D techniques (two-, three-, and four-dimensional ultrasound).

Holoprosencephalia, hypoplasia of corpus callosum and cerebral heterotopia in a male belted Galloway heifer with adipsia

BACKGROUND

Specialized neurons in the diencephalon detect blood hypernatremia in dehydrated animals. These neurons are connected with the pituitary gland, subsequently producing antidiuretic hormone to reabsorb water from urine in the kidneys, and to the forebrain to generate thirst and trigger drinking behavior.

CASE PRESENTATION

This is the first case report describing clinical findings, magnetic resonance imaging (MRI) and necropsy results of a Belted Galloway heifer with severe clinical signs of dehydration and hypernatremia, but concurrent adipsia and isosthenuria. Due to insufficient recovery with symptomatic treatment, owners elected euthanasia. Postmortem MRI and necropsy revealed a complex forebrain malformation: mild abnormal gyrification of the forebrain cortex, lobar holoprosencephaly, and corpus callosum hypoplasia. The affected brain structures are well known to be involved in osmoregulation and generation of thirst in dogs, humans and rodents.

CONCLUSIONS

Complex forebrain malformation can be involved in the pathogenesis of hypernatremia and adipsia in bovines.

Concepts in Multifactorial Etiology of Developmental Disorders: Gene-Gene and Gene-Environment Interactions in Holoprosencephaly

Many common developmental disorders are thought to arise from a complex set of genetic and environmental risk factors. These factors interact with each other to affect the strength and duration of key developmental signaling pathways, thereby increasing the possibility that they fail to achieve the thresholds required for normal embryonic patterning. One such disorder, holoprosencephaly (HPE), serves as a useful model system in understanding various forms of multifactorial etiology. Genomic analysis of HPE cases, epidemiology, and mechanistic studies of animal models have illuminated multiple potential ways that risk factors interact to produce adverse developmental outcomes. Among these are: 1) interactions between driver and modifier genes; 2) oligogenic inheritance, wherein each parent provides predisposing variants in one or multiple distinct loci; 3) interactions between genetic susceptibilities and environmental risk factors that may be insufficient on their own; and 4) interactions of multiple genetic variants with multiple non-genetic risk factors. These studies combine to provide concepts that illuminate HPE and are also applicable to additional disorders with complex etiology, including neural tube defects, congenital heart defects, and oro-facial clefting.

Identifying environmental risk factors and gene-environment interactions in holoprosencephaly

BACKGROUND

Holoprosencephaly is the most common malformation of the forebrain (1 in 250 embryos) with severe consequences for fetal and child development. This study evaluates nongenetic factors associated with holoprosencephaly risk, severity, and gene-environment interactions.

METHODS

For this retrospective case control study, we developed an online questionnaire focusing on exposures to common and rare toxins/toxicants before and during pregnancy, nutritional factors, maternal health history, and demographic factors. Patients with holoprosencephaly were primarily ascertained from our ongoing genetic and clinical studies of holoprosencephaly. Controls included children with Williams-Beuren syndrome (WBS) ascertained through online advertisements in a WBD support group and fliers.

RESULTS

Difference in odds of exposures between cases and controls as well as within cases with varying holoprosencephaly severity were studied. Cases included children born with holoprosencephaly (n = 92) and the control group consisted of children with WBS (n = 56). Pregnancy associated risk associated with holoprosencephaly included maternal pregestational diabetes (9.2% of cases and 0 controls, p = .02), higher alcohol consumption (adjusted odds ratio [aOR], 1.73; 95% CI, 0.88-15.71), and exposure to consumer products such as aerosols or sprays including hair sprays (aOR, 2.46; 95% CI, 0.89-7.19). Significant gene-environment interactions were identified including for consumption of cheese (p < .05) and espresso drinks (p = .03).

CONCLUSION

The study identifies modifiable risk factors and gene-environment interactions that should be considered in future prevention of holoprosencephaly. Studies with larger HPE cohorts will be needed to confirm these findings.

Cdon mutation and fetal alcohol converge on Nodal signaling in a mouse model of holoprosencephaly

Holoprosencephaly (HPE), a defect in midline patterning of the forebrain and midface, arises ~1 in 250 conceptions. It is associated with predisposing mutations in the Nodal and Hedgehog (HH) pathways, with penetrance and expressivity graded by genetic and environmental modifiers, via poorly understood mechanisms. CDON is a multifunctional co-receptor, including for the HH pathway. In mice, Cdon mutation synergizes with fetal alcohol exposure, producing HPE phenotypes closely resembling those seen in humans. We report here that, unexpectedly, Nodal signaling is a major point of synergistic interaction between Cdon mutation and fetal alcohol. Window-of-sensitivity, genetic, and in vitro findings are consistent with a model whereby brief exposure of Cdon mutant embryos to ethanol during gastrulation transiently and partially inhibits Nodal pathway activity, with consequent effects on midline patterning. These results illuminate mechanisms of gene-environment interaction in a multifactorial model of a common birth defect.

A Deletion in GDF7 is Associated with a Heritable Forebrain Commissural Malformation Concurrent with Ventriculomegaly and Interhemispheric Cysts in Cats

An inherited neurologic syndrome in a family of mixed-breed Oriental cats has been characterized as forebrain commissural malformation, concurrent with ventriculomegaly and interhemispheric cysts. However, the genetic basis for this autosomal recessive syndrome in cats is unknown. Forty-three cats were genotyped on the Illumina Infinium Feline 63K iSelect DNA Array and used for analyses. Genome-wide association studies, including a sib-transmission disequilibrium test and a case-control association analysis, and homozygosity mapping, identified a critical region on cat chromosome A3. Short-read whole genome sequencing was completed for a cat trio segregating with the syndrome. A homozygous 7 bp deletion in growth differentiation factor 7 (GDF7) (c.221_227delGCCGCGC [p.Arg74Profs]) was identified in affected cats, by comparison to the 99 Lives Cat variant dataset, validated using Sanger sequencing and genotyped by fragment analyses. This variant was not identified in 192 unaffected cats in the 99 Lives dataset. The variant segregated concordantly in an extended pedigree. In mice, GDF7 mRNA is expressed within the roof plate when commissural axons initiate ventrally-directed growth. This finding emphasized the importance of GDF7 in the neurodevelopmental process in the mammalian brain. A genetic test can be developed for use by cat breeders to eradicate this variant.

Prenatal exposure to pesticides and risk for holoprosencephaly: a case-control study

BACKGROUND

Pesticide exposure during susceptible windows and at certain doses are linked to numerous birth defects. Early experimental evidence suggests an association between active ingredients in pesticides and holoprosencephaly (HPE), the most common malformation of the forebrain in humans (1 in 250 embryos). No human studies to date have examined the association. This study investigated pesticides during multiple windows of exposure and fetal risk for HPE. It is hypothesized that pre-conception and early pregnancy, the time of brain development in utero, are the most critical windows of exposure.

METHODS

A questionnaire was developed for this retrospective case-control study to estimate household, occupational, and environmental pesticide exposures. Four windows of exposure were considered: preconception, early, mid and late pregnancy. Cases were identified through the National Human Genome Research Institute's ongoing clinical studies of HPE. Similarly, controls were identified as children with Williams-Beuren syndrome, a genetic syndrome also characterized by congenital malformations, but etiologically unrelated to HPE. We assessed for differences in odds of exposures to pesticides between cases and controls.

RESULTS

Findings from 91 cases and 56 controls showed an increased risk for HPE with reports of maternal exposure during pregnancy to select pesticides including personal insect repellants (adjusted odds ratio (aOR) 2.89, confidence interval (CI): 0.96-9.50) and insecticides and acaricides for pets (aOR 3.84, CI:1.04-16.32). Exposure to household pest control products during the preconception period or during pregnancy was associated with increased risk for HPE (aOR 2.60, OR: 0.84-8.68). No associations were found for occupational exposures to pesticides during pregnancy (aOR: 1.15, CI: 0.11-11.42), although exposure rates were low. Higher likelihood for HPE was also observed with residency next to an agricultural field (aOR 3.24, CI: 0.94-12.31).

CONCLUSIONS

Observational findings are consistent with experimental evidence and suggest that exposure to personal, household, and agricultural pesticides during pregnancy may increase risk for HPE. Further investigations of gene by environment interactions are warranted.