Large-scale deletions and SMADIP1 truncating mutations in syndromic Hirschsprung disease with involvement of midline structures

Abstract

Hirschsprung disease (HSCR) is a common malformation of neural-crest-derived enteric neurons that is frequently associated with other congenital abnormalities. The SMADIP1 gene recently has been recognized as disease causing in some patients with 2q22 chromosomal rearrangement, resulting in syndromic HSCR with mental retardation, with microcephaly, and with facial dysmorphism. We screened 19 patients with HSCR and mental retardation and eventually identified large-scale SMADIP1 deletions or truncating mutations in 8 of 19 patients. These results allow further delineation of the spectrum of malformations ascribed to SMADIP1 haploinsufficiency, which includes frequent features such as hypospadias and agenesis of the corpus callosum. Thus, SMADIP1, which encodes a transcriptional corepressor of Smad target genes, may play a role not only in the patterning of neural-crest-derived cells and of CNS but also in the development of midline structures in humans.

Figure 1

SMADIP1 deletions. A, Chromosome 2 of patient S.228 and FISH analysis of patient S.259. Left, RTBG karyotype, showing chromosome 2 at 850-band resolution for patient S.228. Right, Metaphase of patient S.259, hybridized with probes BAC 95O9 (SMADIP1) and PAC 164D18 (7qter) as control. B, Haplotype analysis at SMADIP1 locus in patients S.179 and S.203. The poly(CA) microsatellite markers used (and genetic distances [in cM]) are as follows: cen-D2S122-(1.2)-D2S132-(0.5)-D2S381-(0.6)-[D2S298-(?)]-D2S151-tel. SMADIP1 lies between D2S132 and D2S381.

Figure 2

Frontal and profile views of patients presenting with either deletion (A) or mutation (B) of SMADIP1. In the frontal views, note long face with pointed chin, bushy eyebrows, sunken eyes, strabismus, epicanthic folds, saddle nose, thick helix, and fleshy, uplifted earlobes. In the profile views, note sunken eyes, saddle nose, thick helix, and fleshy, uplifted earlobes.

Figure 3

SSCP patterns in patients S.103, S.107, S.230, and S.272. Note the abnormal SSCP pattern in the patients, as compared to their fathers (F) and mothers (M) and to controls (C).

Figure 4

SMADIP1 gene structure. Top, Genomic structure. The SMADIP1 mutations identified are shown by downward-pointing arrows. Bottom, SMADIP1 protein. The four N-terminal and three C-terminal zinc-finger domains (N-ZFD and C-ZFD, respectively), as well as the Smad-binding domain (SBD), are indicated.