Hirschsprung Disease in an Infant with L1 syndrome: Report of a New Case and a novel L1CAM variant

L1cam alternative shorter transcripts encoding the extracellular domains were overexpressed in the intestine of L1cam knockdown mice

Hirschsprung disease (HSCR) is a congenital disorder of functional bowel obstruction due to the absence of enteric ganglia in distal bowel. Different L1cam variants were reportedly associated with L1cam syndrome and HSCR, whose phenotypes lacked predictable relevance to their genotypes. Using next-generation sequencing (NGS), we found an L1CAM de novo frameshift mutation in a female with mild hydrocephalus and skip-type HSCR. A nearly identical L1cam variant was introduced into FVB/NJ mice via the CRISPR-EZ method. A silent mutation was created via ssODN to gain an artificial Ncol restriction enzyme site for easier genotyping. Six L1cam protein-coding alternative transcripts were quantitatively measured. Immunofluorescence staining with polyclonal and monoclonal L1cam antibodies was used to characterize L1cam isoform proteins in enteric ganglia. Fifteen mice, seven males and eight females, generated via CRISPR-EZ, were confirmed to carry the L1cam frameshift variant, resulting in a premature stop codon. There was no prominent hydrocephalus nor HSCR-like presentation in these mice, but male infertility was noticed after observation for three generations in a total of 176 mice. Full-length L1cam transcripts were detected at a very low level in the intestinal tissues and almost none in the brain of these mice. Alternative shorter transcripts encoding the extracellular domains were overexpressed in the intestine of L1cam knockdown mice. Immunofluorescence confirmed no fulllength L1cam protein in enteric ganglia. These shorter L1cam isoform proteins might play a role in protecting L1cam knockdown mice from HSCR.

X-Linked Hydrocephalus with New L1CAM Pathogenic Variants: Review of the Most Prevalent Molecular and Phenotypic Features

Introduction

The underlying molecular defects of congenital hydrocephalus are heterogeneous and many isolated forms of hydrocephalus remain unsolved at the molecular level. Congenital hydrocephalus in males associated with agenesis of the corpus callosum is a notable characteristic of L1CAM gene which is by far the most common genetic etiology of congenital hydrocephalus.

Methods and Results

Sequencing of the L1CAM gene on 25 male patients/fetuses who had been presented with hydrocephalus revealed 6 patients and two fetuses with different hemizygous pathogenic variants. Our study identified 4 novel variants and 4 previously reported. The detection rate was 32%, and all the variants were shown to be maternally inherited. Nonsense variants were detected in 3 patients, while missense variants were detected in 2 patients. Frameshift, silent, and splicing variant, each was detected in 1 patient. The clinical manifestations of the patients are in line with those frequently observed including communicating hydrocephalus and agenesis of the corpus callosum. Moreover, rippled ventricles with subdural collection and asymmetry of ventricles after shunt operation were seen in 1 patient and 2 patients, respectively. In addition, abnormal basal ganglia were found in 4 patients which seems to be an additional distinct new finding. We also describe a patient with novel nonsense variant with the rare association of Hirschsprung's disease. This patient displayed additionally multiple porencephalic cysts and encephalomalacia secondary to hemorrhage due to repeated infections after shunt operation. The patients with the missense variants showed long survival, while those with truncating variants showed poor prognosis.

Conclusion

This report adds knowledge of novel pathogenic variants to the L1CAM variant database. Furthermore, we evaluated the clinical and imaging data of these patients.

Functional Diversity of Neuronal Cell Adhesion and Recognition Molecule L1CAM through Proteolytic Cleavage

The neuronal cell adhesion and recognition molecule L1 does not only 'keep cells together' by way of homophilic and heterophilic interactions, but can also promote cell motility when cleaved into fragments by several proteases. It has largely been thought that such fragments are signs of degradation. Now, it is clear that proteolysis contributes to the pronounced functional diversity of L1, which we have reviewed in this work. L1 fragments generated at the plasma membrane are released into the extracellular space, whereas other membrane-bound fragments are internalised and enter the nucleus, thus conveying extracellular signals to the cell interior. Post-translational modifications on L1 determine the sequence of cleavage by proteases and the subcellular localisation of the generated fragments. Inside the neuronal cells, L1 fragments interact with various binding partners to facilitate morphogenic events, as well as regenerative processes. The stimulation of L1 proteolysis via injection of L1 peptides or proteases active on L1 or L1 mimetics is a promising tool for therapy of injured nervous systems. The collective findings gathered over the years not only shed light on the great functional diversity of L1 and its fragments, but also provide novel mechanistic insights into the adhesion molecule proteolysis that is active in the developing and diseased nervous system.

Analysis of L1CAM gene mutation and imaging appearance in three Chinese families with L1 syndrome: Three case reports

BACKGROUND

The molecular mutations of the L1CAM gene and the imaging appearances of four fetuses with L1 syndrome from three independent Chinese families with a history of hydrocephalus were reported in this study. Two of the three are novel L1CAM variants.

METHODS

Results of clinical and imaging examinations of three Chinese families were collected. Fetal samples were collected by puncture, genomic DNA was extracted, whole-exome sequencing was performed, and the L1CAM gene mutation sites were verified by PCR and Sanger sequencing.

RESULTS

In this case report, we described the imaging appearance and investigated the mutations of the L1CAM gene in three Chinese families with a history of L1 syndrome; these included two nonsense mutations (c.262C>T and c.261C>G) and one splice-site mutation (c.524-1G>A). Two of these three are novel L1CAM variants: c.262C>T and c.261C>G. The results of the sonographic images of the affected fetuses showed severe hydrocephalus. Bilateral lateral ventricles were dilated in the fetuses with c.262C>T and c.261C>G mutations. The left ventricle was about 14 mm wide and the right was about 14 mm in the fetus with c.262C>T mutation. The left ventricle was about 24.9 mm wide and the right was about 23.9 mm in the fetus with c.261C>G mutation. The ultrasound examination of the fetus with c.524-1G>A mutation showed that the third ventricle (7.5 mm wide) was raised, and the fourth ventricle was communicated with the cisterna magna. The parents requested termination of the above pregnancy.

CONCLUSION

The current study emphasizes the importance of combining family history, prenatal ultrasonography, and L1CAM mutation testing positive for the diagnosis of the L1 syndrome.