In order to map the putative HPE gene located on 18p (HPE4) more precisely, six patients with various cytogenetic 18p deletions and clinical features of HPE have been characterized by using a combination of somatic cell hybrid analysis and FISH.
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 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.
Molecular screening of SHH, ZIC2, SIX3, and TGIF genes in patients with features of holoprosencephaly spectrum: Mutation review and genotype-phenotype correlations.
Heterozygous nonsense and missense mutations of the human TGIF gene have been associated with holoprosencephaly, the most common congenital malformation of the forebrain.
We report 22 patients with normal neuropsychological development and a holoprosencephaly-like (HPE-like) phenotype screened for SHH, SIX3, TGIF, and GLI2.
Haploinsufficient mutations in the TG-interacting factor (TGIF) gene were previously identified in a subset of HPE families and sporadic patients, and this gene is located within a region of chromosome 18 that is associated with nonrandom chromosomal aberrations in HPE patients.
These results provide further evidence of a role for TGIF in HPE and demonstrate the importance of functional analysis of putative disease-associated alleles.
These results provide further evidence of a role for TGIF in HPE and demonstrate the importance of functional analysis of putative disease-associated alleles.
These results reveal an important mechanism for the degradation of TGIF through the ubiquitin-proteasome pathway, whose deregulation might contribute to the development of human holoprosencephaly.
Since mutations in the four major genes (SHH, ZIC2, SIX3, and TGIF) have been identified in HPE patients, molecular study is performed routinely in nonsyndromic HPE.
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.
Tgif1 and Tgif2 are transcriptional repressors that limit Transforming Growth Factor β/Nodal signaling, and we show that reducing Nodal signaling in embryos lacking both Tgifs reduces the severity of HPE and partially restores the output of Shh signaling.
Utilizing prospective sequence analysis of SHH, ZIC2, SIX3 and TGIF in holoprosencephaly probands to describe the parameters limiting the observed frequency of mutant gene×gene interactions.