👤 Francesco Nicita

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare inherited white matter disorder. Initially, a "classic" phenotype has been characterized, presenting early-onset macrocephaly, cerebellar ataxia, mild spasticity, and a distinctive neuroimaging pattern of diffuse white matter abnormalities with subcortical cysts. An "improving" phenotype has also been described, featuring milder or absent neurological signs and a remitting pattern on neuroimaging. Mutations in four genes, MLC1, HEPACAM, GPRC5B and AQP4 have been associated with MLC. We describe clinical and genetic features of a cohort of genetically confirmed Italian MLC patients, representing the largest Italian cohort reported to date. We conducted a retrospective, multicenter, observational study. Patients were included based on clinical and neuroimaging features consistent with MLC, along with a confirmed genetic diagnosis. Data were collected using a standardized database and included demographic, clinical, neuroimaging, neurophysiological, and genetic information. Thirty-three patients from eight Italian centers were enrolled. Twenty-seven harbored biallelic MLC1 variants (23 distinct mutations, including three novel variants), while six had three distinct heterozygous HEPACAM variants. All MLC1-mutated patients exhibited the "classic" phenotype, frequently accompanied by orthopedic, gastrointestinal, and respiratory comorbidities. HEPACAM-mutated patients were consistent with the "improving" phenotype. No patients harbored mutations in GPRC5B or AQP4. Our findings expand the mutational spectrum of MLC1, further characterize the disease phenotype, and provide valuable insights into its presence in Italy. They also underscore management needs of individuals with MLC, highlighting the importance of multidisciplinary care. Show less

Microtubule-actin cross-linking factor 1 (MACF1) is a large protein of the spectraplakin family, which is essential for brain development. MACF1 interacts with microtubules through the growth arrest-specific 2 (Gas2)-related (GAR) domain. Heterozygous MACF1 missense variants affecting the zinc-binding residues in this domain result in a distinctive cortical and brain stem malformation. Evidence for other MACF1-associated disorders is still limited. Here, we present a cohort of 45 individuals with heterozygous or bi-allelic MACF1 variants to explore the phenotypic spectrum and assess possible pathogenic relevance. We observe that de novo heterozygous missense variants in the EF-hand domains also result in distinctive brain malformation and provide experimental evidence that variants in the EF-hand/GAR module increase microtubule binding, suggestive of a toxic gain of function. Notably, no phenotype-genotype correlation was possible for the remaining heterozygous variants in other domains. A clinical review of eight families with bi-allelic variants reveals a possible complex neurodevelopmental syndrome of the central and peripheral nervous systems. In these individuals, bi-allelic variants mostly affect the Plakin domain. Furthermore, RNA sequencing and chromatin immunoprecipitation (ChIP) analyses of human fetal brain tissue reveal five MACF1 isoforms with region-specific expression, differing in their exon 1 transcription start sites but splicing to a common exon 2. This differential expression explains the frontal-predominant lissencephaly in an individual with a homozygous stop-gain in exon 1 (MACF1-204: c.70C>T [p.Arg24∗]), as this isoform is preferentially expressed in the frontal cortex. We conclude that MACF1-related disorders are strictly linked to domain function and the level of transcript expression, explaining the observed wide clinical heterogeneity. Show less