Severe microcephaly

Gene: LMNB2

The mode of inheritance of this gene has been updated to BOTH monoallelic and biallelic, autosomal or pseudoautosomal following NHS Genomic Medicine Service approval.

Created: 11 Mar 2026, 5:26 p.m. | Last Modified: 11 Mar 2026, 5:26 p.m.

Panel Version: 8.34

Green List (high evidence)

PMID: 40011009 reports two related babies who were homozygous for a loss-of-function LMNB2 variant. Both babies shared a similar phenotype of severe brain development abnormalities and died during the perinatal period. This shared phenotype was reflected in several Lmnb2-deficient mouse models.
Material from the patient’s fibroblasts (obtained at birth) were used in Western blot and immunofluorescence cell labelling, and confirmed the complete absence of lamin B2 and revealed an increase in lamin B1, together with alterations in alpha-tubulin and vimentin organisation. (PMID: 40011009).

Created: 9 Apr 2025, 10:27 a.m. | Last Modified: 9 Apr 2025, 10:28 a.m.

Panel Version: 7.25

The rating of this gene has been updated following NHS Genomic Medicine Service approval.

Created: 10 Mar 2022, 10:52 a.m. | Last Modified: 10 Mar 2022, 10:52 a.m.

Panel Version: 2.282

Not associated with a relevant phenotype in OMIM or in Gen2Phen. PMID 33033404 reports five individuals with heterozygous variants in LMNB2. One of these cases was de novo for c.160A>C p.N54H (NM_032737.4) and the remaining cases had c.1192G>A, p.Glu398Lys (NM_032737.4), which was shown to be de novo in two cases, inherited from the unaffected mother (who was mosaic for the variant) and the inheritance in the remaining case was not established. All of these cases had moderate to severe developmental delay and microcephaly.

Created: 24 Nov 2020, 12:04 p.m. | Last Modified: 24 Nov 2020, 12:04 p.m.

Panel Version: 2.44

Comment on list classification: There is enough evidence for this gene to be rated GREEN at the next major review.

Created: 24 Nov 2020, 12:03 p.m. | Last Modified: 24 Nov 2020, 12:03 p.m.

Panel Version: 2.44

Mode of inheritance
BOTH monoallelic and biallelic, autosomal or pseudoautosomal

Green List (high evidence)

Parry et al (2020 - PMID: 33033404) in a study to identify novel microcephaly genes using the DDD and 100k genomes project (100kGP) patient cohort, report on the phenotype of 13 individuals with heterozygous variant in LMNB1 (N=7) and LMNB2 (N=6).

LMNB1 : The authors identified 3 recurrent variants (c.97A>G - p.Lys33Glu (3), c.97_99del - p.Lys33del (2) , c.269G>C - p.Arg90Pro (2) / NM_005573.4) in seven individuals (3 from the DDD study, 4 from the 100kGP). In all cases were segregation studies were possible, the variant had occurred as a de novo event.

LMNB2 : 4 individuals from the DDD cohort and 1 from the 100kGP were found to harbor the same missense SNV (NM_032737.4:c.1192G>A, p.Glu398Lys). The variant had occurred de novo in 3 subjects and was inherited from a mosaic - unaffected - parent in a further case. Another individual was found to harbor c.160A>C - p.Asn54His.

LMNB1/2 common phenotypes :
All cases had congenital microcephaly (OFC -5.85 +/- 1.14 SD) apart from one individual, without history of IUGR or postnatally abnormal height (the latter in most).

Neuroimaging suggested structurally normal brain without abnormal migration. Gyral simplification / global reduction in white matter / increased extra axial spaces / enlarged ventricles were reported in 2.

LMNB1 - Global developmental delay was a feature in all (mild to severe) with some having occasional words at 7y (P3), absent speech (P9 - age category 5-10y) or ID not further specified (P13).

LMNB2 - DD was a feature in all 6 subjects (5/6 moderate to severe - 1/6 GDD). 5/6 were 10y or older with language (in 3 language not achieved) and motor deficits (walking not achieved in 1/6 - occurred at the age of 6y in 1/6).

Facial features were not consistent nor suggestive of a syndromic diagnosis (sloping forehead in some).

Overall, as the authors comment, the phenotype corresponded to a severe nonsyndromic microcephaly (although additional features were reported in some).

Animal model:
Microcephaly is supported by Lmnb1 ko mouse model. Lmnb1/2 ko mice however display migration defects, while Lmnb2 ko mice do not have reduced size at birth. Heterozygous Lmnb1 mice do not present microcephaly. It is suggested that while animal models support a similar (to the human) phenotype the underlying mechanism is different.

Variant effect :
variants were shown to affect highly conserved residues within the lamin a-helical rod-domain. As affected residues are conserved in LMNA, modelling with available LMNA PDB structures, suggested disrupted interactions required for higher-order assembly of lamin filaments.

Recurrence of specific variants at specific residues, absence of pLoF ones, the htz mouse Lmnb1 phenotype (absence of microcephaly) and the proposed mechanism (perturbation of complex formation) suggest a gain-of-function/dominant-negative effect rather than happloinsufficiency.

[Please also note the additional OMIM phenotypes for LMNB1 / LMNB2 - not here reviewed]
Sources: Literature

Created: 17 Oct 2020, 12:09 p.m.

Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown

Phenotypes
Congenital microcephaly; Global developmental delay; Intellectual disability

Publications

• 33033404

Mode of pathogenicity
Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments