A novel splice variant expands the LAMC3-associated cortical phenotype to frontal only polymicrogyria and adult-onset epilepsy

Novel LAMC3 pathogenic variant enriched in Finnish population causes malformations of cortical development and severe epilepsy

OBJECTIVE

Recessive LAMC3 mutations are recognized to cause epilepsy with cortical malformations characterized by polymicrogyria and pachygyria. The objective of this study was to describe the clinical picture and epilepsy phenotype of four patients with a previously undescribed LAMC3 variant.

METHODS

All epilepsy patients treated in Kuopio Epilepsy Center (located in Kuopio, Finland) are offered the possibility to participate in a scientific study investigating biomarkers in epilepsy (Epibiomarker study). We have collected a comprehensive database of the study population, and are currently re-evaluating our database regarding the patients with developmental and/or epileptic encephalopathy (DEE). If the etiology of epilepsy remains unknown in the clinical setting, we are performing whole exome sequencing to recognize the genetic causes.

RESULTS

Among our study population of 323 DEE patients we recognized three patients with similar homozygous LAMC3 c.1866del (p.(Phe623Serfs*10)) frameshift variant and one patient with a compound heterozygous mutation where the same frameshift variant was combined with an intronic LAMC3 c.4231-12C>G variant on another allele. All these patients have severe epilepsy and either bilateral agyria-pachygyria or bilateral polymicrogyria in their clinical MRI scanning. Cortical malformations involve the occipital lobes in all our patients. Epilepsy phenotype is variable as two of our patients have DEE with epileptic spasms progressing to Lennox-Gastaut syndrome and intellectual disability. The other two patients have focal epilepsy without marked cognitive deficit. The four patients are unrelated. LAMC3 c.1866del p.(Phe623Serfs*10) frameshift variant is enriched in the Finnish population.

SIGNIFICANCE

Only a few patients with epilepsy caused by LAMC3 homozygous or compound heterozygous mutations have been described in the literature. To our knowledge, the variants discovered in our patients have not previously been published. Clinical phenotype appears to be more varied than previously assumed and patients with a milder phenotype and normal cognition have probably remained unrecognized.

Case report: LAMC3-associated cortical malformations: Case report of a novel stop-gain variant and literature review

Background: Malformations of cortical development (MCDs) can lead to peculiar neuroradiological patterns and clinical presentations (i.e., seizures, cerebral palsy, and intellectual disability) according to the specific genetic pathway of the brain development involved; and yet a certain degree of phenotypic heterogeneity exists even when the same gene is affected. Here we report a man with an malformations of cortical development extending beyond occipital lobes associated with a novel stop-gain variant in LAMC3. Case presentation: The patient is a 28-year-old man suffering from drug-resistant epilepsy and moderate intellectual disability. He underwent a brain magnetic resonance imaging showing polymicrogyria involving occipital and temporal lobes bilaterally. After performing exome sequencing, a novel stop-gain variant in LAMC3 (c.3871C>T; p. Arg1291*) was identified. According to the cortical alteration of the temporal regions, temporal seizures were detected; instead, the patient did not report occipital seizures. Different pharmacological and non-pharmacological interventions (i.e., vagus nerve stimulation) were unsuccessful, even though a partial seizure reduction was obtained after cenobamate administration. Conclusion: Our case report confirms that variants of a gene known to be related to specific clinical and neuroradiological pictures can unexpectedly lead to new phenotypes involving different areas of the brain.

A New Case With Cortical Malformation Caused by Biallelic Variants in LAMC3

Objective

In this study, we report the case of a 24-year-old man with intellectual disability and childhood-onset seizures. This patient had newly identified biallelic variants in the laminin subunit gamma 3 (LAMC3) gene with unreported cortical malformation.

Methods

Exome sequencing.

Results

Genetic analyses revealed new biallelic variants in the LAMC3 gene. An MRI examination of the brain revealed cortical malformations predominantly in the temporal lobes and mildly in the occipital, frontal, and parietal lobes. In addition, our patient also exhibited mild midline malformation in the ventral pons, which is unique to LAMC3 variants.

Discussion

Patients with LAMC3 variants have been reported to exhibit cortical malformation predominantly in the occipital lobes, but this patient exhibited cortical malformation predominantly in the temporal lobes and mildly in the occipital, frontal, and parietal lobes. In addition, this patient also exhibited mild midline malformation in the ventral pons. These unique findings cast new light on the role of LAMC3 in brain development.