Central nervous system in twin reversed arterial perfusion sequence with special reference to examination of the brain in acardius anceps

EPAS 1, congenital heart disease, and high altitude: disclosures by genetics, bioinformatics, and experimental embryology

The high-altitude environment is a challenge for human settlement. Low oxygen concentrations, extreme cold, and a harsh arid climate are doubtlessly challenges for the colonization of the Tibetan plateau. I am delighted to comment on the article of Pan et al. (2018) on mutations in endothelial PAS domain-containing protein 1 (EPAS1) in congenital heart disease in Tibetans. In humans, the EPAS1 gene is responsible for coding EPAS1 protein, an alias of which is HIF2α, an acronym for hypoxia-inducible factor 2 alpha. EPAS1 is a type of hypoxia-inducible factors, which are collected as a group of transcription factors involved in body response to oxygen level. EPAS1 gene is active under hypoxic conditions and plays an essential role in the development of the heart and in the management of the catecholamine balance, mutations of which have been identified in neuroendocrine tumors. In this article, Pan et al. investigated Tibetan patients with and without non-syndromic congenital heart disease. They identified two novel EPAS1 gene mutations, of which N203H mutation significantly affected the transcription activity of the vascular endothelial growth factor (VEGF) promoter, particularly in situations of hypoxia. VEGF is a downstream target of HIF-2 (other than HIF-1), and the expression levels of either HIF-1α or HIF-2α correlate positively to VEGF expression. Pan et al.'s data may be of incitement to further evaluate protein-protein interaction and using experimental animal models. Moreover, it may also be a stimulus for setting up genetic epidemiologic studies for other populations living at high altitudes.

Holoprosencephaly-polydactyly (pseudotrisomy 13) syndrome: case report and diagnostic criteria

We report a new case of a fetus with holoprosencephaly-polydactyly syndrome, also known as pseudo-trisomy 13 syndrome, and no other apparent abnormalities except for septal agenesis of the left lung. The fetal karyotype was normal. Mutational analysis of five genes (SHH, SIX3, TGIF, ZIC2, and GLI3), which are major genes associated with holoprosencephaly, did not disclose any mutational findings. We therefore propose that the abnormalities of our fetus support the demarcation of this syndrome as an autonomous phenotype. Specific diagnostic criteria for holoprosencephaly-polydactyly syndrome need to be complemented by the absence of mutations in the major holoprosencephaly genes.

An acardiac twin with advanced brain development and a minor form of holoprosencephaly and intracerebral retina-like pigmented tissue: a case report and review of the literature

The development of an acardiac twin in a monochorionic multiple pregnancy is a rare and severe complication of abnormal placental vascular anastomoses. These malformed fetuses present with a very bizarre morphology and a plethora of different malformations. However, all acardiac twins show either a complete absence or an anlage of the heart. Cerebral development is usually poor. We report, according to our review of the literature, for the first time, a very unusual case of acardius with features of acardius amorphus and acormus (fused head and malformed axial skeleton without macroscopically detectable internal organs) with lobar holoprosencephaly and intracerebral pigmented retina-like tissue.

Cyclopia, aprosencephaly, and acardiac twinning: Is hypoxia-ischemia a unifying mechanism?

In a recent case of monochorionic diamniotic twinning we observed one twin with acardia, cyclopia, and aprosencephaly, an association not reported previously. In most cases of acardia, the development of tissues in superior regions of the body is disrupted severely, while inferior structures develop more normally. A common explanation for this disruption is hypoxia-ischemia due to twin reversed arterial perfusion (TRAP). In this condition, arterial-arterial and venous-venous anastomoses in the placenta permit twin-twin transfusion and reversal of blood flow in the umbilical vessels and aorta of the recipient twin. The heart is absent or severely deficient, either by secondary atrophy or possibly a more primary, though currently unknown, mechanism. As a result, cranial tissues are less likely to be perfused with oxygenated blood than caudal tissues. A host of craniocerebral anomalies are observed in acardia, including total absence of the head and brain, rudimentary brain, anencephaly, holoprosencephaly, neuronal migration defects, and near-normal brain. Hypoxia-ischemia could be an important factor in the disruption of tissues in the present case, although a more generalized process affecting heart, head, and brain cannot be excluded. The findings suggest that hypoxia-ischemia may play a role in the pathogenesis of some cases of holoprosencephaly and aprosencephaly. This mechanism has been underreported and requires additional investigation.

Monozygotic twins discordant for frontonasal malformation

Frontonasal malformation (FNM), also known as the median cleft face syndrome, encompasses a spectrum of phenotypes that are believed to result from a single underlying aetiology. Over the course of two decades, the Craniofacial Unit at the Radcliffe Infirmary, Oxford has been involved in the management of six same-sex twins where only a single twin is affected. With local ethical committee approval, five sets of twins were traced and consented to participation in this study. Monozygosity of all five twin pairs was confirmed, and the clinical features were reviewed. We discuss the mechanistic relationship between FNM and the twinning process and the genetic implications of this association.

Hydranencephaly owing to twin-twin transfusion: serial fetal ultrasonography and magnetic resonance imaging findings

We report a newborn girl with hydranencephaly. In the setting of a monochorionic twin pregnancy, one twin's demise was detected by ultrasonography at 18 weeks of gestation, apparently the result of a twin-twin transfusion. In the surviving twin, the evolution of ventriculomegaly, first noted at 18 weeks, to hydranencephaly at 27 weeks is documented by serial sonograms. These findings were confirmed with fetal and postnatal magnetic resonance imaging.

Neuropathological features of the brain in acardius acormus

Acardia is the most severe complication in monozygotic twinning. Acardius acormus is an uncommon phenotype among acardias. We report on an acardius acormus using thorough gross and light microscopic examination of the brain. Neuropathological examination revealed a severely disorganized cerebral cortex, agenesis of cerebellum and brain stem, and undeveloped basal ganglia and thalamus. In particular, the cerebral cortex was characterized by no clear lamination, almost complete loss of neurons, extensive gliosis, angiogenesis and focal mineralization. Neurohistology of the acardius acormus clearly demonstrated two types of lesions: developmental arrest of the brain and hypoxic-asphyxic damage to the brain with reactive gliosis and angiogenesis. Both types of lesions may be induced by the same teratogen: early onset of persisting hypoxia due to a reversed arterial perfusion. The quality of the description contributes valuably to a better understanding of the basic mechanism underlying the acardius phenotype.