L-serine treatment is associated with improvements in behavior, EEG, and seizure frequency in individuals with GRIN-related disorders due to null variants

Pathogenic missense variants in GRIN2A and GRIN2B may result in gain or loss of function (GoF/LoF) of the N-methyl-D-aspartate receptor (NMDAR). This observation gave rise to the hypothesis of successfully treating GRIN-related disorders due to LoF variants with co-agonists of the NMDAR. In this respect, we describe a retrospectively collected series of ten individuals with GRIN2A- or GRIN2B-related disorders who were treated with L-serine, each within an independent n-of-1 trial. Our cohort comprises one individual with a LoF missense variant with clinical improvements confirming the above hypothesis and replicating a previous n-of-1 trial. A second individual with a GoF missense variant was erroneously treated with L-serine and experienced immediate temporary behavioral deterioration further supporting the supposed functional pathomechanism. Eight additional individuals with null variants (that had been interpreted as loss-of-function variants despite not being missense) again showed clinical improvements. Among all nine individuals with LoF missense or null variants, L-serine treatment was associated with improvements in behavior in eight (89%), in development in four (44%), and/or in EEG or seizure frequency in four (44%). None of these nine individuals experienced side effects or adverse findings in the context of L-serine treatment. In summary, we describe the first evidence that L-serine treatment may not only be associated with clinical improvements in GRIN-related disorders due to LoF missense but particularly also null variants. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13311-021-01173-9

Clinical, neuroradiological and molecular characterization of cerebellar dysplasia with cysts (Poretti-Boltshauser syndrome)

Cerebellar dysplasia with cysts and abnormal shape of the fourth ventricle, in the absence of significant supratentorial anomalies and of muscular involvement, defines recessively inherited Poretti-Boltshauser syndrome (PBS). Clinical features comprise non-progressive cerebellar ataxia, intellectual disability of variable degree, language impairment, ocular motor apraxia and frequent occurrence of myopia or retinopathy. Recently, loss-of-function variants in the LAMA1 gene were identified in six probands with PBS. Here we report the detailed clinical, neuroimaging and genetic characterization of 18 PBS patients from 15 unrelated families. Biallelic LAMA1 variants were identified in 14 families (93%). The only non-mutated proband presented atypical clinical and neuroimaging features, challenging the diagnosis of PBS. Sixteen distinct variants were identified, which were all novel. In particular, the frameshift variant c.[2935delA] recurred in six unrelated families on a shared haplotype, suggesting a founder effect. No LAMA1 variants could be detected in 27 probands with different cerebellar dysplasias or non-progressive cerebellar ataxia, confirming the strong correlate between LAMA1 variants and PBS