Extension of the Clinicoradiologic Spectrum of Newly Described End-Truncating LAMB1 Variations

OBJECTIVES: To refine the clinical spectrum of a very recently identified phenotype associated with LAMB1 end-truncating pathogenic variations. METHODS: Detailed clinical, neuropsychological, and MRI investigation of 6 patients from 2 unrelated families segregating end-truncating LAMB1 variations. RESULTS: All patients harbored a LAMB1 end-truncating pathogenic variation. The specific association of a hippocampal type episodic memory dysfunction and a diffuse leukoencephalopathy was observed in all 4 patients aged older than 50 years, slightly worsening over time in 2 patients with several years of follow-up. Additional unspecific neurologic symptoms are reported, such as episodes of numbness, language troubles, or faintness in these 4 patients and the 2 younger ones. DISCUSSION: The association of an extensive leukoencephalopathy with an episodic memory dysfunction of the hippocampal type is strongly suggestive of a LAMB1 end-truncating variation in adults older than 50 years. Early cognitive complaints and imaging abnormalities might exist decades before. Additional transient manifestations can be observed, and this association should lead to LAMB1 screening to avoid unnecessary invasive investigations.