Here, we analyze seven reported missense mutations (G31R, D88V, Q100H, N115K, W117G, W117R, and E188Q) that alter the N-terminal signaling domain of Shh protein, and show that two of these mutations (Q100H and E188Q), which are questionably linked to HPE, produce no detectable effects on function.
These results provide further evidence of a role for TGIF in HPE and demonstrate the importance of functional analysis of putative disease-associated alleles.
The mutational spectrum of holoprosencephaly-associated changes within the SHH gene in humans predicts loss-of-function through either key structural alterations of the ligand or its altered synthesis.
Heterozygous GLI2 loss of function mutations in humans have been reported in holoprosencephaly (HPE), HPE-like phenotypes associated with pituitary anomalies and combined pituitary hormone deficiency with or without other extra-pituitary findings.
Frank holoprosencephaly was present in 11 individuals with deletions of one of the common HPE genes SHH, ZIC2, SIX3, and TGIF1, in one individual with a deletion of the HPE8 locus at 14q13, and in one individual with a deletion of FGF8, whereas deletions of other HPE loci and candidate genes (FOXA2 and LRP2) expressed microforms of HPE.
We performed mutational analysis in the four main HPE causing genes (SHH, SIX3, TGIF, and ZIC2) and GLI3, a gene associated with polydactyly as well as fluorescent in situ hybridization (FISH) to search for microdeletions in these genes and two candidate HPE genes (DISP1 and FOXA2).
Holoprosencephaly (HPE) is genetically heterogeneous with four genes, SIX3, SHH, TGIF, and ZIC2 that have been identified to date and that are altered in 12% of patients.
We report here that whereas mice lacking the Cdo paralog Boc do not have HPE, Cdo;Boc double mutants on a largely Cdo-resistant genetic background have lobar HPE with strong craniofacial anomalies and defects in Shh target gene expression in the developing forebrain.
Mutations in the SHH gene are the most common cause of sporadic and inherited holoprosencephaly (HPE), a developmental disorder that is characterized by defective prosencephalon development.
We investigated 127 HPE probands by sequencing their TGIF gene and identified the first nonsense mutation reported so far and also a novel missense mutation, in two families that presented a large range of disease severity.
These functions are very likely conserved among bilaterians since vertebrate six3 is required for neuroendocrine and median brain development with certain mutations leading to holoprosencephaly.
Holoprosencephaly (HPE) is genetically heterogeneous with four genes, SIX3, SHH, TGIF, and ZIC2 that have been identified to date and that are altered in 12% of patients.
Mutations in GLI2 have been found in association with holoprosencephaly (HPE) and HPE-like phenotype, with and without pituitary hormone deficiencies; as well as in patients with pituitary dysfunction with and without HPE craniofacial features.
Numerous genetic loci and environmental factors are implicated in HPE, but mutation in the sonic hedgehog (Shh) gene is an established cause in both humans and mice.
Our data indicate that in a subset of patients SCH may develop as one aspect of a more complex malformation of the ventral forebrain, directly result from mutations in the SHH pathway and hence be considered as yet another feature of the broad phenotypic spectrum of holoprosencephaly.
However, the family presented here is unique as none of the three identified individuals with a GLI2 deletion showed any typical signs of holoprosencephaly, whereas all patients reported so far were referred for genetic testing because at least one member exhibited holoprosencephaly and related features.