DO: 0051014;
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
Gene/Locus |
Gene/Locus MIM number |
|---|---|---|---|---|---|---|
| 5q23.2 | Leukodystrophy, demyelinating, adult-onset, autosomal dominant, atypical | 621061 | Autosomal dominant | 3 | LMNB1 | 150340 |
A number sign (#) is used with this entry because of evidence that atypical autosomal dominant adult-onset demyelinating leukodystrophy (ADLDAT) is caused by heterozygous deletion involving regulatory elements upstream of the LMNB1 gene (150340) on chromosome 5q23.
One patient with ADLDAT resulting from an inverted duplication involving the LMNB1 gene and a contiguous topologically associating domain (TAD) has been identified (see CYTOGENETICS).
Atypical autosomal dominant adult-onset demyelinating leukodystrophy (ADLDAT) is a slowly progressive neurologic disorder characterized by pyramidal signs with weakness and spasticity, dysarthria, dysautonomia, and white matter alterations affecting the cerebrum and corticospinal tracts while sparing the cerebellum. Atypical ADLD can be distinguished from typical ADLD by lack of early involvement of the autonomic nervous system and sparing of the cerebellum clinically and on brain imaging (Dimartino et al., 2024).
Typical ADLD (ADLDTY; 169500), which shows overlapping clinical features, but more commonly presents with significant autonomic symptoms and clinical and radiographic cerebellar involvement, is caused by heterozygous duplications of 5q23 involving the LMNB1 gene (Dimartino et al., 2024).
Quattrocolo et al. (1997) reported a large multigenerational family from northern Italy with adult-onset atypical leukoencephalopathy. Patients presented in the fifth decade with insidious and variable symptoms, including gait impairment, pyramidal signs (in most), lower limb weakness/paraplegia, action tremor, dysarthria, and dysphagia. The full clinical picture included spastic quadriparesis, pseudobulbar dysfunction, and urinary incontinence. Cognition was mostly spared. Brain imaging showed marked atrophy of the cerebral cortex and white matter signal abnormalities in the cortex and brainstem, with sparing of the cerebellum.
Brussino et al. (2010) reported follow-up of the Italian family (ADLD-1-TO) reported by Quattrocolo et al. (1997), noting that the disorder had some distinguishing features from typical ADLD in that the Italian family lacked autonomic involvement and had sparing of the cerebellar white matter on brain imaging. Patient-derived lymphoblasts showed increased LMNB1 expression, consistent with a diagnosis of ADLD.
Giorgio et al. (2015) reported follow-up of family ADLD-1-TO. Postmortem examination of an affected individual showed overexpression of LMNB1 in the cortical frontal lobe. Patient fibroblasts showed accumulation of LMNB1 within the nuclear lamina, abnormal nuclear morphology, and a 44% increase in nuclear rigidity compared to controls. Genetic analysis identified a heterozygous deletion upstream of the LMNB1 gene that affected gene expression via an enhancer adoption mechanism (see CYTOGENETICS).
Nmezi et al. (2019) reported 5 patients from 3 unrelated families (DEL1 of East Asian origin, DEL2 of Northern European origin, and DEL3 of Northern European and Native American origin) with atypical ADLD associated with heterozygous deletions upstream of the LMNB1 gene on chromosome 5q23. The patients had onset of neurologic symptoms between 32 and 52 years of age. Common features included hand tremor, hand incoordination, hypophonia, dysarthria, progressive spasticity of the upper and lower limbs, brisk reflexes, and extensor plantar responses. Sensory examinations were normal. Three patients had autonomic symptoms, including orthostatic hypotension and urinary urgency. Three patients had ocular/extraocular abnormalities, such as interrupted saccades, nystagmus, and optic disc pallor. Three patients died between 36 and 59 years of age. Brain imaging showed white matter hyperintensities in the frontal lobes, cerebral peduncles, and corticospinal tract. Some patients reported worsening of neurologic deficit with infection or environmental heat.
In a postmortem histopathologic study of a patient with atypical ADLD, Dimartino et al. (2024) found patchy myelin and abnormal astrocytes in the cerebral white matter, but sparing of the cerebellar white matter, which had normal myelin staining and morphologically normal astrocytes.
The transmission pattern of atypical ADLD in the Italian family (ADLD-1-TO) reported by Quattrocolo et al. (1997) and Brussino et al. (2010) was consistent with autosomal dominant inheritance.
By linkage analysis of a multigenerational Italian family (ADLD-1-TO) with atypical ADLD, Brussino et al. (2010) found linkage to a region on chromosome 5q23 that included the LMNB1 gene (Zmax of 6.83 at marker D5S2955), but no point mutations or copy number defects were detected in LMNB1.
Using custom array CGH to analyze affected members of the Italian family (ADLD-1-TO) with atypical ADLD described by Brussino et al. (2010), Giorgio et al. (2015) identified a heterozygous 660-kb deletion on chromosome 5q23 that included 3 genes: PHAX (604924), ALDH7A1 (107323), and GRAMD3 (GRAMD2B; 620182), with the closest deletion boundary located 66 kb upstream of the LMNB1 gene. The deletion was not present in the Database of Genomic Variants or in 100 Italian control individuals. Analysis of the breakpoint regions suggested that the deletion was mediated by Alu elements. In vitro studies showed that single-copy loss of the PHAX, ALDH7A1, and GRAMD3 genes did not affect LMNB1 expression, and deletion of these genes was considered unlikely to contribute to disease pathogenesis. A circular chromosome conformation capture (4C) analysis and expression studies in patient fibroblasts showed that the deletion resulted in repositioning of a forebrain-specific enhancer element closer to the LMNB1 promoter ('enhancer adoption'). The findings were consistent with the mainly cerebral localization of LMNB1 overexpression and myelin degeneration in affected members of this family.
In 5 patients from 3 unrelated families with atypical ADLD, Nmezi et al. (2019) identified 3 different unique and nonrecurrent heterozygous deletions of chromosome 5q23 upstream of the LMNB1 gene. The deletions ranged in size from 250 to 670 kb.
Using high-throughput chromosome conformation capture (Hi-C) techniques to analyze topologically associating domains (TADs), Dimartino et al. (2024) found that patients with atypical ADLD (Giorgio et al., 2015; Nmezi et al., 2019) carried inter-TAD deletions upstream of the LMNB1 promoter and variably included several genes (PHAX, ALDH7A1, and GRAMD3), a TAD boundary, and the LMNB1 regulatory element. The deletions resulted in the removal of a crucial LMNB1 regulatory element and shuffled TAD formation, thus allowing ectopic interactions between the LMNB1 promoter and regulatory elements of other genes ('enhancer adoption').
Atypical ADLD Caused by Inverted Duplication
Giorgio et al. (2013) reported a patient (patient BR1) with an atypical form of ADLD associated with a heterozygous inverted duplication of 5q23 involving several genes, including LMNB1.
Dimartino et al. (2024) stated that patient BR1 of Giorgio et al. (2013), with atypical ADLD, had a 475-kb inverted inter-TAD duplication that encompassed the LMNB1 gene, but extended centromerically to include the boundary and part of the contiguous TAD, also causing shuffled TAD formations and ectopic interactions between regulatory elements.
Brussino, A., Vaula, G., Cagnoli, C., Panza, E., Seri, M., Di Gregorio, E., Scappaticci, S., Camanini, S., Daniele, D., Bradac, G. B., Pinessi, L., Cavalieri, S., Grosso, E., Migone, N., Brusco, A. A family with autosomal dominant leukodystrophy linked to 5q23.2-q23.3 without lamin B1 mutations. Europ. J. Neurol. 17: 541-549, 2010. [PubMed: 19961535] [Full Text: https://doi.org/10.1111/j.1468-1331.2009.02844.x]
Dimartino, P., Zadorozhna, M., Yumiceba, V., Basile, A., Cani, I., Melo, U. S., Henck, J., Breur, M., Tonon, C., Lodi, R., Brusco, A., Pippucci, T., and 12 others. Structural variants at the LMNB1 locus: deciphering pathomechanisms in autosomal dominant adult-onset demyelinating leukodystrophy. Ann. Neurol. 96: 855-870, 2024. [PubMed: 39078102] [Full Text: https://doi.org/10.1002/ana.27038]
Giorgio, E., Robyr, D., Spielmann, M., Ferrero, E., Di Gregorio, E., Imperiale, D., Vaula, G., Stamoulis, G., Santoni, F., Atzori, C., Gasparini, L., Ferrera, D., Canale, C., Guipponi, M., Pennacchio, L. A., Antonarakis, S. E., Brussino, A., Brusco, A. A large genomic deletion leads to enhancer adoption by the lamin B1 gene: a second path to autosomal dominant adult-onset demyelinating leukodystrophy (ADLD). Hum. Molec. Genet. 24: 3143-3154, 2015. [PubMed: 25701871] [Full Text: https://doi.org/10.1093/hmg/ddv065]
Giorgio, E., Rolyan, H., Kropp, L., Chakka, A. B., Yatsenko, S., Di Gregorio, E., Lacerenza, D., Vaula, G., Talarico, F., Mandich, P., Toro, C., Pierre, E. E., and 26 others. Analysis of LMNB1 duplications in autosomal dominant leukodystrophy provides insights into duplication mechanisms and allele-specific expression. Hum. Mutat. 34: 1160-1171, 2013. Note: Erratum: Hum. Mutat. 35: 149 only, 2014. [PubMed: 23649844] [Full Text: https://doi.org/10.1002/humu.22348]
Nmezi, B., Giorgio, E., Raininko, R., Lehman, A., Spielmann, M., Koenig, M. K., Adejumo, R., Knight, M., Gavrilova, R., Alturkustani, M., Sharma, M., Hammond, R., Gahl, W. A., Toro, C., Brusco, A., Padiath, Q. S. Genomic deletions upstream of lamin B1 lead to atypical autosomal dominant leukodystrophy. Neurol. Genet. 5: e305, 2019. [PubMed: 30842973] [Full Text: https://doi.org/10.1212/NXG.0000000000000305]
Quattrocolo, G., Leombruni, S., Vaula, G., Bergui, M., Riva, A., Bradac, G. B., Bergamini, L. Autosomal dominant late-onset leukoencephalopathy: clinical report of a new Italian family. Europ. Neurol. 37: 53-61, 1997. [PubMed: 9018034] [Full Text: https://doi.org/10.1159/000117406]