The main clinical feature is progressive microcephaly, with measurements ranging from -3.6 to -12 SD. In some individuals, height was also affected, but less prominent. Global developmental delay and intellectual disability of varying severity was seen in all affected individuals. Seizures are present in about half of the individuals. Neuroimaging demonstrated a structurally normal brain in most of them, although a simplified gyral pattern and abnormal corpus callosum have been reported. Major malformations were not reported. In the most severely affected individuals, severe hypotonia, visual impairment, scoliosis and feeding problems were present. There is no typical facial gestalt.
Note: Duplication of the entire LMNB1 gene causes adult-onset autosomal dominant leukodystrophy (ADLD [MIM 169500]), which needs to be differentiated from the microcephaly phenotype.