External hydrocephalus as a prenatal feature of noonan syndrome

Genetic and molecular mechanisms of hydrocephalus

Hydrocephalus is a neurological condition caused by aberrant circulation and/or obstructed cerebrospinal fluid (CSF) flow after cerebral ventricle abnormal dilatation. In the past 50 years, the diagnosis and treatment of hydrocephalus have remained understudied and underreported, and little progress has been made with respect to prevention or treatment. Further research on the pathogenesis of hydrocephalus is essential for developing new diagnostic, preventive, and therapeutic strategies. Various genetic and molecular abnormalities contribute to the mechanisms of hydrocephalus, including gene deletions or mutations, the activation of cellular inflammatory signaling pathways, alterations in water channel proteins, and disruptions in iron metabolism. Several studies have demonstrated that modulating the expression of key proteins, including TGF-β, VEGF, Wnt, AQP, NF-κB, and NKCC, can significantly influence the onset and progression of hydrocephalus. This review summarizes and discusses key mechanisms that may be involved in the pathogenesis of hydrocephalus at both the genetic and molecular levels. While obstructive hydrocephalus can often be addressed by removing the obstruction, most cases require treatment strategies that involve merely slowing disease progression by correcting CSF circulation patterns. There have been few new research breakthroughs in the prevention and treatment of hydrocephalus.

Non-invasive prenatal detection of dominant single-gene disorders in fetal structural abnormalities: a clinical feasibility study

OBJECTIVE

This study evaluated the accuracy of non-invasive prenatal testing (NIPT-SGDs) for dominant monogenic genetic diseases associated with fetal structural abnormalities and to assess the feasibility of clinical application.

METHODS

Pregnant women requiring prenatal diagnosis due to fetal structural abnormalities were enrolled. Maternal peripheral blood was analyzed for cell-free DNA (cfDNA) using coordinative allele-aware target enrichment sequencing (COATE-seq). This assessed fetal allele depth distribution, fraction and variation ratio. The variation's origin was then determined to obtain fetal variation information. Finally, NIPT-SGDs results were confirmed via invasive prenatal diagnosis (IPD).

RESULTS

Upon examination of 113 samples using NIPT-SGDs, COATE-seq successfully analyzed 112 for fetal variation, excluding one due to hemolysis. The study detected six positive cases, yielding a 5.36% detection rate. These disorders included tuberous sclerosis complex (TSC1 and TSC2 being its causative genes), Noonan syndrome (PTPN11), polycystic kidney disease (PKD1), and Kabuki syndrome (KMT2D), occurring twice each, except for Noonan and polycystic kidney disease. Two false positives were due to the mother being a genetic mosaicism. Compared to invasive whole-exome sequencing (WES), NIPT-SGDs did not detect nine positive cases of IPD dominant monogenic diseases, accurately identifying 90.18% (101/112) of the actual positive and negative cases.

CONCLUSION

Our findings demonstrate the clinical utility of NIPT-SGDs using COATE-seq in effectively identifying fetuses with dominant single-gene disorders. Furthermore, this method can be applied to all fetuses.

Prenatal Sonographic Features of Noonan Syndrome: Case Series and Literature Review

Noonan syndro me is a rare autosomal dominant congenital abnormality associated with a gene defect located on the short arm of chromosome 12. It is characterized by dysmorphic facies, webbed neck, short stature, lymphatic obstruction, cardiac anomalies, and intellectual disability. Prenatal diagnosis of Noonan syndrome is rare because there are no pathognomonic sonographic signs. Studies on the prenatal sonographic features of Noonan syndrome have been reported in very limited numbers. This case series of severe fetal Noonan syndrome, together with a literature review, was conducted to establish prenatal sonographic features highly suggestive of Noonan syndrome to facilitate early detection by clinicians. This study reveals that Noonan syndrome has a relatively specific pattern, which facilitates prenatal molecular genetic diagnosis. Increased nuchal translucency (NT) in the late first trimester and fluid collection in the early second trimester could be warning signs for follow-up, prompting further investigation to detect late-onset features and leading to molecular genetic confirmation. Most structural abnormalities appear in the second trimester, with progressive changes noted throughout gestation. This review better characterizes the sonographic features of fetal Noonan syndrome based on a larger sample size, illustrating a wider spectrum of prenatal phenotypes, including lymphatic drainage disorders, cardiac abnormalities, polyhydramnios, and absent ductus venosus.

The homozygous pathogenic variant of the POMGNT1 gene identified using whole-exome sequencing in Iranian family with congenital hydrocephalus

Background

Hydrocephalus is one of the most common pathophysiological disabilities with a high mortality rate, which occurs both congenitally and acquired. It is estimated that genetic components are the etiology for up to 40% of hydrocephalus cases; however, causal mutations identified until now could only explain approximately 20% of congenital hydrocephalus (CH) patients, and most potential hydrocephalus-associated genes have yet to be determined. This study sought to find causal variations in a consanguineous family with four affected children diagnosed with hydrocephalus.

Material and methods

In this study, we evaluated twenty-five members of an extended family consisting of a nuclear family with four affected children resulting from a consanguineous couple and eighteen of their relatives, including one hydrocephalus case. The mother of this family was experiencing her 15th week of pregnancy, and cytogenetic evaluation was performed using amniocentesis to identify fetal chromosomal abnormalities. We conducted whole-exome sequencing (WES) on the genomic DNA of the proband to detect the CH-causing variants, followed by confirmation and segregation analysis of the detected variant in the proband, fetus, and family members through Sanger sequencing.

Results

Following the bioinformatic analysis and data filtering, we found a homozygous variant [NM_001243766.2:c.74G>A:p.W25X] within the protein O-mannose beta-1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) gene confirmed by Sanger sequencing in the proband and segregated with the hydrocephalus in the family. The variant was described as pathogenic and regarded as a nonsense-mediated mRNA decay (NMD) due to the premature stop codon, which results in a truncated protein.

Conclusion

The results of the current study broadened the mutational gene spectrum of CH and our knowledge of the hydrocephalus etiology by introducing a novel homozygous variant within the POMGNT1 gene, which had never been previously reported solitary in these patients.

Noonan syndrome: Neuroimaging findings and morphometric analysis of the cranium base and posterior fossa in children

BACKGROUND AND PURPOSE

There are a few studies regarding intracranial findings in neonates with Noonan syndrome (NS); however, there are no quantitative analyses in a pediatric population. The aim of this study was to find characteristic intracranial abnormalities and to quantitatively analyze the posterior fossa and cranium base in children with NS.

METHODS

A total of 30 patients (11 females and 19 males, mean age 13.1 ± 4.3 years) were retrospectively identified between July 2017 and June 2022. Twenty-one patients had MRI. Age at MRI examination, sex, genetic mutations, and clinical findings were noted. In patients with MRI, the presence of white matter lesions, basal ganglia lesions, corpus callosum abnormalities, sellar/parasellar lesions, and tonsillar ectopia was noted. For morphometric analysis, cerebellar diameter, vermis and clivus heights, cranial base, tentorial and infratentorial angles, and McRae's and Twining's lines were each measured twice by two radiologists individually.

RESULTS

The most common lesions were focal white matter lesions, followed by abnormalities of the splenium of the corpus callosum. The cerebellar diameter, vermis and clivus heights, Twining's line, and infratentorial angle were significantly smaller; cranial base angle and tentorial angle were significantly larger in NS (p < .05). Interrater and intrarater agreements were the highest for cerebellar diameter and the lowest for tentorial angle measurements.

CONCLUSION

Children with NS had characteristic callosal and tentorial findings and neuroimaging findings similar to other RASopathies. This study also shows that a small posterior fossa and flattening of the cranial base are present in children with NS, which may aid in diagnosis.

Detailed prenatal and postnatal MRI findings and clinical analysis of RAF1 in Noonan syndrome

Noonan syndrome is a genetically heterogeneous developmental disorder, which usually includes findings such as short stature, facial dysmorphia, cardiac abnormalities and a varying degree of intellectual disability. We present a unique case of a rare variant of Noonan syndrome in a very preterm female infant born at 28 + 4 gestational weeks, with abnormal radiological findings visible at fetal magnetic resonance imaging (MRI) and evolution of the brain lesions during infancy.

Molecular Mechanisms and Risk Factors for the Pathogenesis of Hydrocephalus

Hydrocephalus is a neurological condition due to the aberrant circulation and/or obstruction of cerebrospinal fluid (CSF) flow with consequent enlargement of cerebral ventricular cavities. However, it is noticed that a lot of patients may still go through symptomatic progression despite standard shunting procedures, suggesting that hydrocephalus is far more complicated than a simple CSF circulative/obstructive disorder. Growing evidence indicates that genetic factors play a fundamental role in the pathogenesis of some hydrocephalus. Although the genetic research of hydrocephalus in humans is limited, many genetic loci of hydrocephalus have been defined in animal models. In general, the molecular abnormalities involved in the pathogenesis of hydrocephalus include brain development and ependymal cell dysfunction, apoptosis, inflammation, free radical generation, blood flow, and cerebral metabolism. Moreover, recent studies have indicated that the molecular abnormalities relevant to aberrant cerebral glymphatic drainage turn into an attractive subject in the CSF circulation disorder. Furthermore, the prevalent risk factors could facilitate the development of hydrocephalus. In this review, we elicited some possible fundamental molecular mechanisms and facilitating risk factors involved in the pathogenesis of hydrocephalus, and aimed to widen the diagnosis and therapeutic strategies for hydrocephalus management. Such knowledge could be used to improve patient care in different ways, such as early precise diagnosis and effective therapeutic regimens.