Novel <scp>LAMA1</scp> Mutations in a Pedigree With Poretti‐Boltshauser Syndrome: Implications for Hypomyelination

BACKGROUND: Poretti-Boltshauser syndrome (PBS) is an autosomal recessive disorder caused by biallelic pathogenic variants in the LAMA1 gene, typically presenting with cerebellar dysplasia and fourth ventricle abnormalities. While neurological and ocular manifestations are well recognized, an association between LAMA1 variants and central nervous system (CNS) dysmyelination has not been previously established, and the underlying mechanisms remain unexplored. CASE PRESENTATION: We report two pediatric siblings from a single family with novel compound heterozygous LAMA1 variants [c.505C>T (p.Arg169Ter) and c.634del (p.Ser212HisfsTer28)]. Both patients presented with classic PBS features including ataxia, developmental delay, and oculomotor apraxia. Neuroimaging confirmed cerebellar dysplasia and fourth ventricle abnormalities. Notably, we observed the unexpected concurrence of cerebral white matter hypomyelination, a finding rarely associated with PBS. CONCLUSIONS: This report presents the first clinical evidence linking novel LAMA1 variants to cerebral hypomyelination in PBS, based on the concordant observation in two affected siblings from the same family. Its specific association with LAMA1-related PBS had not been clearly delineated previously. Drawing on insights from the literature, we hypothesize that LAMA1 dysfunction may disrupt key stages of oligodendrocyte precursor cell biology, specifically survival, proliferation, migration, and differentiation, providing a potential mechanistic basis for the CNS hypomyelination observed in our patients. These findings expand both the phenotypic and genotypic spectrum associated with LAMA1 mutations and offer new insights into possible mechanisms of CNS hypomyelination in PBS.