Holoprosencephaly: Review of Embryology, Clinical Phenotypes, Etiology and Management

Congenital external hydrocephalus: A rare presentation of lobar holoprosencephaly in a neonate

External hydrocephalus is a rare condition characterized by abnormal cerebrospinal fluid (CSF) accumulation in the subarachnoid space, often associated with developmental anomalies. Lobar holoprosencephaly, a milder form of holoprosencephaly, can manifest with hydrocephalus due to its impact on brain development and CSF dynamics. This case report describes a neonate with congenital external hydrocephalus secondary to lobar holoprosencephaly, highlighting the diagnostic imaging findings and management approach. A neonate presented with progressive macrocephaly, irritability, altered sensorium, and poor feeding. Antenatal ultrasound at 32 weeks of gestation revealed macrocephaly and hydrocephalus, leading to a cesarean delivery at 38 weeks. Physical examination showed an occipitofrontal circumference of 45 cm, exceeding the 97th percentile for age. Magnetic resonance imaging (MRI) revealed fused frontal horns of the lateral ventricles, hypoplasia of the posterior corpus callosum, and extensive extra-axial CSF accumulation compressing the brain parenchyma. The CSF collection showed complete suppression on FLAIR imaging, confirming its nature, and a cortical vein sign indicated an enlarged subarachnoid space rather than a subdural hygroma. A diagnosis of lobar holoprosencephaly with congenital external hydrocephalus was made. The patient underwent peritoneal shunting to alleviate intracranial pressure, significantly reducing head circumference to 38 cm. Postoperative recovery was uneventful, and the parents were counseled on genetic testing and long-term follow-up. This case underscores the importance of detailed neuroimaging in differentiating external hydrocephalus from other pathologies and highlights the role of surgical intervention in improving outcomes. Early diagnosis and a multidisciplinary approach are vital for managing complex congenital anomalies such as lobar holoprosencephaly.

Lobar holoprosencephaly with associated meningocele: A rare case report of a 25-year-old patient with multiple seizures

Lobar holoprosencephaly (HPE) represents the mildest form of HPE, featuring an interhemispheric fissure extending along most of the entire midline, with the thalami remaining unfused. Lobar HPE is usually diagnosed in the prenatal stage or infancy; however, cases of adult-onset are exceedingly rare. Here, we present a 25-year-old patient who was presented with multiple episodes of seizures and was subsequently diagnosed with lobar HPE accompanied by a meningocele. By shedding light on this rare brain malformation, we hope to raise awareness among healthcare professionals and stimulate further research into the pathogenesis, clinical course, and management of adult-onset HPE.

Developmental, Endocrine, and Ophthalmologic Outcomes in Children Prenatally Diagnosed With Midline Brain Malformations

BACKGROUND

Midline brain malformations (MBMs) are commonly prenatally diagnosed and associated with endocrinologic, ophthalmic, and adverse developmental outcomes.

METHODS

A retrospective review was conducted of all neonates identified prenatally with suspected MBMs between 2018 and 2022 at the only multidisciplinary referral center in a multistate region. Abnormalities were categorized as isolated versus complicated absent cavum septum pellucidum (ASP) (N = 11 vs N = 13) or corpus callosum abnormalities (AgCC) (N = 11 vs N = 43) or holoprosencephaly spectrum (N = 12). We assessed subsequent diagnoses and outcomes using a standardized assessment pathway.

RESULTS

Infants with holoprosencephaly were significantly more likely to die than patients with isolated ASP or AgCC (P = 0.02). Surviving infants with holoprosencephaly had universal developmental delay, significantly more than the 10% seen in isolated ASP or AgCC (P = 0.007), and infants with isolated MBMs were significantly more likely to be alive and without endocrine, ophthalmologic, developmental, or epileptic diagnoses at last follow-up than other groups (isolated ASP = 67%, AgCC 82%). The median time to diagnosis of optic nerve hypoplasia was 3 days and initial identification of endocrine concerns was 7 days. There were no significant differences between rates of diagnosis for endocrine, ophthalmologic, or epileptic complications between groups, with all MBMs demonstrating a risk for complications.

CONCLUSIONS

Our study shows the importance of multidisciplinary screening in all infants with midline brain defects. Most infants with isolated ASP or AgCC did not have MBM-associated diagnoses at last follow-up, but all groups had comorbidities and would benefit from multispecialty postnatal monitoring.

Prenatal identification of a pathogenic maternal FGFR1 variant in two consecutive pregnancies with fetal forebrain malformations

OBJECTIVE

Holoprosencephaly (HPE) is the most common aberration of forebrain development, and it leads to a wide spectrum of developmental and craniofacial anomalies. HPE etiology is highly heterogeneous and includes both chromosomal abnormalities and single-gene defects.

METHODS

Here, we report an FGFR1 heterozygous variant detected by prenatal exome sequencing and inherited from the asymptomatic mother, in association with recurrent neurological abnormalities in the HPE spectrum in two consecutive pregnancies.

RESULTS

Individuals with germline pathogenic variants in FGFR1 (MIM: 136350) show extensive phenotypic variability, which ranges from asymptomatic carriers to hypogonadotropic hypogonadism, arhinencephaly, Kallmann's syndrome with associated features such as cleft lip and palate, skeletal anomalies, isolated HPE, and Hartsfield syndrome.

CONCLUSION

The presented case supports the role of exome sequencing in prenatal diagnosis when fetal midline structural anomalies are suggestive of a genetic etiology, as early as the first trimester of gestation. The profound heterogeneity of FGFR1 allelic disorders needs to be considered when planning prenatal screening even in asymptomatic carriers.

CNOT1 p.Arg535Cys variant in holoprosencephaly with late onset diabetes mellitus

Holoprosencephaly (HPE) results from a lack of cleavage of the prosencephalon. It has a complex etiology, resulting from chromosome abnormalities or single gene variants in the Sonic hedgehog signaling pathway. A single variant, p.Arg535Cys in CNOT1, has been described in HPE in association with pancreatic agenesis and neonatal diabetes. Here, we report on a case of HPE and p.Arg535Cys in CNOT1 without pancreatic agenesis where the patient presented with diabetes mellitus in adolescence. This case reinforces the role of CNOT1 in pancreatic development. We suggest that individuals with p.Arg535Cys in CNOT1 with no pancreas abnormalities observed at birth should be screened for diabetes during follow-up.

Alobar Holoprosencephaly in a Newborn: A Case Report of Prenatal Diagnosis and a Review of the Literature

Holoprosencephaly (HPE) is a severe and complex congenital brain malformation caused by a defect in the midline cleavage of the prosencephalon during early embryonic development. It is the most common prosencephalic malformation in humans and is categorized into three classical forms based on the severity of this cleavage defect: alobar, semilobar, and lobar HPE. A milder interhemispheric variant, called syntelencephaly, is also considered a form of HPE. This condition may arise from genetic, environmental, or teratogenic factors. Patients with HPE often present with facial dysmorphia, with severity generally correlating with the extent of brain malformation. HPE is diagnosed prenatally through ultrasound and brain magnetic resonance imaging (MRI). Through this case report and a review of the literature, we discuss the etiopathogenic and diagnostic aspects of HPE, along with the management of this congenital malformation, illustrated by the antenatal diagnosis of a newborn with alobar HPE, confirmed by brain MRI at 32 days of age.

A review of neurogenetics in fetal and neonatal clinical medicine

This review of neurogenetics serves as a primer for clinicians practicing in fetal-neonatal medicine. The review provides an update on neurogenetics, understanding the language of genetics, genetic testing approaches, and interpretation of genetic test results. Common examples of neurogenetic disease in fetal-neonatal medicine are used to enhance basic concepts. The results of genetic testing and their implications for patients and families are outlined. Genetics is becoming foundational to clinical practice across specialties. The advances are improving the speed of diagnosis, facilitating early treatments, and improving outcomes in neurogenetic disorders. A basic understanding of genetics is foundational to appropriate clinical-decision making and interpretation of those results to describe common fetal-neonatal neurological phenotypes.

The Role of Antenatal Ultrasound Scans in the Early Detection of Alobar Holoprosencephaly: A Case Report

Holoprosencephaly (HPE) is a developmental defect that affects the brain structure due to failure or incomplete division of the prosencephalon at the third week to the fourth week of gestation into cerebral hemispheres. Although the exact cause of HPE remains unclear, it is suspected to result from a combination of genetic and environmental factors. We report a case of alobar HPE. This case was diagnosed on antenatal ultrasonography in a 42-year-old female (Gravida 3, Para 2) with an unremarkable family history and absence of any risk factors. The association of alobar HPE with an atrioventricular canal defect, left-sided clubfoot, and omphalocele, in this case, constitutes a rare fetal morphological presentation. This case highlights the crucial role of regular antenatal ultrasound scans in the early detection of fatal anomalies like alobar HPE.

Use of an Orthodontic and Otolaryngological Approach in an Infant with Holoprosencephaly

Holoprosencephaly is a complex human brain malformation resulting from incomplete cleavage of the prosencephalon into both hemispheres. Congenital nasal pyriform aperture stenosis (CNPAS) is sometimes found in patients with mild forms of holoprosencephaly. Surgical treatment is required. Low-invasive surgical approaches involve balloon dilation of the pyriform opening. We present the case of an 8-day-old girl diagnosed with holoprosencephaly, CNPAS, and the presence of a solitary median maxillary central incisor. Once examined by neonatologist, geneticist, pneumologist, otolaryngologist, and pediatric dentist, a combined otolaryngological-orthodontic approach was used. The obstruction of the right nasal cavity was treated by widening the nasal cavities and stabilizing them with a balloon dilation technique. After surgery, the respiratory space was increased by applying a neonatal palatal expander plate (NPEP) considering the palatal deformity: ogival shaped, anterior vertex growth direction, reduction of transverse diameters. The NPEP promoted distraction of the median palatine suture and assisted the nasal dilation. Therefore, after the insertion of NPEP, the physiological sucking-swallowing mechanism was activated. In infants with CNPAS, NPEP can be useful to ensure the safe stability of nasal dilation. A multidisciplinary approach is fundamental. In our experience, the close collaboration between an otolaryngologist and orthodontist is essential for the management of the patient with CNPAS.

Prdm15 acts upstream of Wnt4 signaling in anterior neural development of Xenopus laevis

Mutations in PRDM15 lead to a syndromic form of holoprosencephaly (HPE) known as the Galloway-Mowat syndrome (GAMOS). While a connection between PRDM15, a zinc finger transcription factor, and WNT/PCP signaling has been established, there is a critical need to delve deeper into their contributions to early development and GAMOS pathogenesis. We used the South African clawed frog Xenopus laevis as the vertebrate model organism and observed that prdm15 was enriched in the tissues and organs affected in GAMOS. Furthermore, we generated a morpholino oligonucleotide-mediated prdm15 knockdown model showing that the depletion of Prdm15 leads to abnormal eye, head, and brain development, effectively recapitulating the anterior neural features in GAMOS. An analysis of the underlying molecular basis revealed a reduced expression of key genes associated with eye, head, and brain development. Notably, this reduction could be rescued by the introduction of wnt4 RNA, particularly during the induction of the respective tissues. Mechanistically, our data demonstrate that Prdm15 acts upstream of both canonical and non-canonical Wnt4 signaling during anterior neural development. Our findings describe severe ocular and anterior neural abnormalities upon Prdm15 depletion and elucidate the role of Prdm15 in canonical and non-canonical Wnt4 signaling.