Subcortical band heterotopia (SBH), also known as doublecortex syndrome, is a malformation of cortical development resulting from mutations in the doublecortin gene (DCX).
The effect of several mutations leading to lissencephaly and double-cortex syndrome can be traced to the domain swap and the proposed self-association of doublecortin.
Our first classification of LIS and subcortical band heterotopia (SBH) was developed to distinguish between the first two genetic causes of LIS-LIS1 (PAFAH1B1) and DCX.
A novel DCX missense mutation in a family with X-linked lissencephaly and subcortical band heterotopia syndrome inherited from a low-level somatic mosaic mother: Genetic and functional studies.
Mutations in the microtubule-associated protein doublecortin (DCX) cause type I (X-linked or XLIS) lissencephaly in hemizygous males and subcortical band heterotopia (SBH) in females, with defects in neuron migration during development affecting cortical lamination.
Mutations were somatic in 8 of the 27 (30%), predominantly in persons with the double-cortex syndrome (in whom we found mutations in DCX and LIS1), persons with periventricular nodular heterotopia (FLNA), and persons with pachygyria (TUBB2B).
Taken as a whole, these observations demonstrate that DCX-related disorders are clinically heterogeneous, with severe sporadic and milder familial subcortical band heterotopia, each associated with specific DCX mutations.
An ovel mutation (c.83_84delAT, p.Tyr28Phefs*31) was identified in LIS1 in 1 of the boys with lissencephaly and another novel mutation (c.200delG, p.Ile68Leufs*87) was found in DCX in the girl with subcortical band heterotopia.
This finding points to the possible implication of mosaic deletions in the DCX gene in unexplained forms of SBH and may allow for detection of SBH prenatally.
We describe a 2-year-old girl affected by SBH with epilepsy and periodic limb movements (PLMs), in whom a novel "de novo" missense substitution, Met1Val (M1V), was identified in the DCX gene.
Full chromosome studies in the parents and the proband and mutation analysis on peripheral blood lymphocytes (and on skin cultured fibroblasts from affected and unaffected skin areas in the child) in the genes for subcortical band heterotopia (DCX (Xq22.3-q23)], lissencephaly (PAFAH1B1, alias LIS1, at 17p13.3), and oculocerebrorenal syndrome of Lowe (OCRL at Xq23-q24)] were unrevealing.
Lissencephaly-pachygyria and subcortical band heterotopia (SBH) are disorders of neuronal migration and represent a malformative spectrum resulting from mutations of either LIS1 or DCX genes.
Identifying these mechanisms has shed light on typical human neuronal migration disorders such as periventricular heterotopias (disorder of migration initiation linked to filamin), type I lissencephaly (cytoskeletal abnormality linked to Lis1, a microtubule-associated protein), double cortex syndrome (cytoskeletal abnormality linked to doublecortin, a microtubule-associated protein), or lissencephaly plus cerebellar hypoplasia (reelin defect).
Mutation(s) in the LIS1 gene or the X-linked gene doublecortin (DCX) results in a spectrum of disorders including lissencephaly, or "smooth brain", and subcortical band heterotopia, or "doublecortex".
This selective sparing of memory functions has not been previously reported in individuals with SBH and suggests that doublecortin does not play a role in the development of memory systems in the mesial temporal region, which tend to be spared in SBH.
X-linked isolated lissencephaly sequence (XLIS) and subcortical band heterotopia (SBH) are allelic disorders caused by mutations in the doublecortin (DCX) gene.