LMNB1 mutation causes cerebellar involvement and a genome instability defect

The role of Lamin B2 in human diseases

Lamin B2 (LMNB2), on the inner side of the nuclear envelope, constitutes the nuclear skeleton by connecting with other nuclear proteins. LMNB2 is involved in a wide range of nuclear functions, including DNA replication and stability, regulation of chromatin, and nuclear stiffness. Moreover, LMNB2 regulates several cellular processes, such as tissue development, cell cycle, cellular proliferation and apoptosis, chromatin localization and stability, and DNA methylation. Besides, the influence of abnormal expression and mutations of LMNB2 has been gradually discovered in cancers and laminopathies. Therefore, this review summarizes the recent advances of LMNB2-associated biological roles in physiological or pathological conditions, with a particular emphasis on cancers and laminopathies, as well as the potential mechanism of LMNB2 in related cancers.

Adult Hereditary White Matter Diseases With Psychiatric Presentation: Clinical Pointers and MRI Algorithm to Guide the Diagnostic Process

OBJECTIVE

The investigators aimed to provide clinical and MRI guidelines for determining when genetic workup should be considered in order to exclude hereditary leukoencephalopathies in affected patients with a psychiatric presentation.

METHODS

A systematic literature review was conducted, and clinical cases are provided. Given the central role of MRI pattern recognition in the diagnosis of white matter disorders, the investigators adapted an MRI algorithm that guides the interpretation of MRI findings and thus directs further investigations, such as genetic testing.

RESULTS

Twelve genetic leukoencephalopathies that can present with psychiatric symptoms were identified. As examples of presentations that can occur in clinical practice, five clinical vignettes from patients assessed at a referral center for adult genetic leukoencephalopathies are provided.

CONCLUSIONS

Features such as drug-resistant symptoms, presence of long-standing somatic features, trigger events, consanguinity, and positive family history should orient the clinician toward diagnostic workup to exclude the presence of a genetic white matter disorder. The identification of MRI white matter abnormalities, especially when presenting a specific pattern of involvement, should prompt genetic testing for known forms of genetic leukoencephalopathies.

De Novo Variants in LMNB1 Cause Pronounced Syndromic Microcephaly and Disruption of Nuclear Envelope Integrity

Lamin B1 plays an important role in the nuclear envelope stability, the regulation of gene expression, and neural development. Duplication of LMNB1, or missense mutations increasing LMNB1 expression, are associated with autosomal-dominant leukodystrophy. On the basis of its role in neurogenesis, it has been postulated that LMNB1 variants could cause microcephaly. Here, we confirm this hypothesis with the identification of de novo mutations in LMNB1 in seven individuals with pronounced primary microcephaly (ranging from -3.6 to -12 SD) associated with relative short stature and variable degree of intellectual disability and neurological features as the core symptoms. Simplified gyral pattern of the cortex and abnormal corpus callosum were noted on MRI of three individuals, and these individuals also presented with a more severe phenotype. Functional analysis of the three missense mutations showed impaired formation of the LMNB1 nuclear lamina. The two variants located within the head group of LMNB1 result in a decrease in the nuclear localization of the protein and an increase in misshapen nuclei. We further demonstrate that another mutation, located in the coil region, leads to increased frequency of condensed nuclei and lower steady-state levels of lamin B1 in proband lymphoblasts. Our findings collectively indicate that de novo mutations in LMNB1 result in a dominant and damaging effect on nuclear envelope formation that correlates with microcephaly in humans. This adds LMNB1 to the growing list of genes implicated in severe autosomal-dominant microcephaly and broadens the phenotypic spectrum of the laminopathies.