Intragenic deletion in the LARGE gene causes Walker-Warburg syndrome

Abstract

Intragenic homozygous deletions in the Large gene are associated with a severe neuromuscular phenotype in the myodystrophy (myd) mouse. These mutations result in a virtual lack of glycosylation of alpha-dystroglycan. Compound heterozygous LARGE mutations have been reported in a single human patient, manifesting with mild congenital muscular dystrophy (CMD) and severe mental retardation. These mutations are likely to retain some residual LARGE glycosyltransferase activity as indicated by residual alpha-dystroglycan glycosylation in patient cells. We hypothesized that more severe LARGE mutations are associated with a more severe CMD phenotype in humans. Here we report a 63-kb intragenic LARGE deletion in a family with Walker-Warburg syndrome (WWS), which is characterized by CMD, and severe structural brain and eye malformations. This finding demonstrates that LARGE gene mutations can give rise to a wide clinical spectrum, similar as for other genes that have a role in the post-translational modification of the alpha-dystroglycan protein.

Fig. 1

Phenotype and brain CT scans of patient 1 (a–c) and patient 2 (d–f). Patient 1 showed no dysmorphic features, severe generalized hypotonia with very little spontaneous movements of the limbs, and valgus deformity of the feet (a). Brain CT of patient 1 (b, c), and patient 2 (e, f) show absence of the inferior cerebellar vermis, a hypoplastic cerebellum, and marked dilatation of the lateral ventricles. Patient 2 also shows severe hydrocephalus with wide fontanel and separated sutures and cysts (d–f)

Fig. 2

Family pedigree. Females are represented by circles, males by squares. Open symbols represent the unaffected family members, the solid black symbols the WWS affected siblings

Fig. 3

MLPA analysis, showing a deletion of two exonic probes (EX9 and EX10) and two flanking intronic probes (IN8-2 and IN10) in the patient (diamonds), and in the unaffected carriers (black circles, triangles, and squares). No intronic probes were tested for the patient due to limited availability of DNA. Open circles, triangles, and squares depict control individuals

Fig. 4

Schematic overview of LARGE exons 8–11 of wild-type sequence (a) and patient sequence (b), showing the exons depicted by black boxes and the MLPA probes depicted by black bars. MLPA analysis revealed deletion of four MLPA probes (IN8-2, EX9, EX10, and IN10). Sequence analysis of the breakpoint region in the patient revealed the exact position of the 63.1 kb deletion (c)