A welcome mat for leprosy and Lassa fever

Walker-Warburg syndrome and tectocerebellar dysraphia: A novel association caused by a homozygous DAG1 mutation

OBJECTIVES

To elaborate the imaging phenotype associated with a homozygous c.743C > del frameshift mutation in DAG1 leading to complete absence of both α- and β-dystroglycan previously reported in a consanguineous Israeli-Arab family.

METHODS

We analyzed prenatal and postnatal imaging data of patients from a consanguineous Israeli-Arab kindred harboring the DAG1 mutation.

RESULTS

The imaging studies (fetal ultrasound, CT scan and postnatal MRI) demonstrated: flat cortex (abnormally thick with irregular pebbled cortical-white matter border on MRI), hydrocephalus, scattered small periventricular heterotopia and subependymal hemorrhages and calcifications, z-shaped brainstem, and in addition an occipital encephalocele, vermian agenesis, and an elongated and thick tectum (tectocerebellar dysraphia).

CONCLUSIONS

The novel association of cobblestone malformation with tectocerebellar dysraphia as part of WWS is characteristic of the homozygous c.743C > del frameshift mutation in the DAG1 gene.

Brain dystrophin, neurogenetics and mental retardation

Duchenne muscular dystrophy (DMD) and the allelic disorder Becker muscular dystrophy (BMD) are common X-linked recessive neuromuscular disorders that are associated with a spectrum of genetically based developmental cognitive and behavioral disabilities. Seven promoters scattered throughout the huge DMD/BMD gene locus normally code for distinct isoforms of the gene product, dystrophin, that exhibit nervous system developmental, regional and cell-type specificity. Dystrophin is a complex plasmalemmal-cytoskeletal linker protein that possesses multiple functional domains, autosomal and X-linked homologs and associated binding proteins that form multiunit signaling complexes whose composition is unique to each cellular and developmental context. Through additional interactions with a variety of proteins of the extracellular matrix, plasma membrane, cytoskeleton and distinct intracellular compartments, brain dystrophin acquires the capability to participate in the modulatory actions of a large number of cellular signaling pathways. During neural development, dystrophin is expressed within the neural tube and selected areas of the embryonic and postnatal neuraxis, and may regulate distinct aspects of neurogenesis, neuronal migration and cellular differentiation. By contrast, in the mature brain, dystrophin is preferentially expressed by specific regional neuronal subpopulations within proximal somadendritic microdomains associated with synaptic terminal membranes. Increasing experimental evidence suggests that in adult life, dystrophin normally modulates synaptic terminal integrity, distinct forms of synaptic plasticity and regional cellular signal integration. At a systems level, dystrophin may regulate essential components of an integrated sensorimotor attentional network. Dystrophin deficiency in DMD/BMD patients and in the mdx mouse model appears to impair intracellular calcium homeostasis and to disrupt multiple protein-protein interactions that normally promote information transfer and signal integration from the extracellular environment to the nucleus within regulated microdomains. In DMD/BMD, the individual profiles of cognitive and behavioral deficits, mental retardation and other phenotypic variations appear to depend on complex profiles of transcriptional regulation associated with individual dystrophin mutations that result in the corresponding presence or absence of individual brain dystrophin isoforms that normally exhibit developmental, regional and cell-type-specific expression and functional regulation. This composite experimental model will allow fine-level mapping of cognitive-neurogenetic associations that encompass the interrelationships between molecular, cellular and systems levels of signal integration, and will further our understanding of complex gene-environmental interactions and the pathogenetic basis of developmental disorders associated with mental retardation.