Intellectual disability, coarse face, relative macrocephaly, and cerebellar hypotrophy in two sisters.

We report on two Portuguese sisters with a very similar phenotype characterized by severe intellectual disability, absent speech, relative macrocephaly, coarse face, cerebellar hypotrophy, and severe ataxia. Additional common features include increased thickness of the cranial vault, delayed dental eruption, talipes equino-varus, clinodactyly, and camptodactyly of the fifth finger. The older sister has retinal dystrophy and the younger sister has short stature. Their parents are consanguineous. We suggest this condition constitutes a previously unreported autosomal recessive entity.

Tbx22null mice have a submucous cleft palate due to reduced palatal bone formation and also display ankyloglossia and choanal atresia phenotypes.

Craniofacial defects involving the lip and/or palate are among the most common human birth defects. X-linked cleft palate and ankyloglossia results from loss-of-function mutations in the gene encoding the T-box transcription factor TBX22. Further studies show that TBX22 mutations are also found in around 5% of non-syndromic cleft palate patients. Although palate defects are obvious at birth, the underlying developmental pathogenesis remains unclear. Here, we report a Tbx22(null) mouse, which has a submucous cleft palate (SMCP) and ankyloglossia, similar to the human phenotype, with a small minority showing overt clefts. We also find persistent oro-nasal membranes or, in some mice a partial rupture, resulting in choanal atresia. Each of these defects can cause severe breathing and/or feeding difficulties in the newborn pups, which results in approximately 50% post-natal lethality. Analysis of the craniofacial skeleton demonstrates a marked reduction in bone formation in the posterior hard palate, resulting in the classic notch associated with SMCP. Our results suggest that Tbx22 plays an important role in the osteogenic patterning of the posterior hard palate. Ossification is severely reduced after condensation of the palatal mesenchyme, resulting from a delay in the maturation of osteoblasts. Rather than having a major role in palatal shelf closure, we show that Tbx22 is an important determinant for intramembranous bone formation in the posterior hard palate, which underpins normal palate development and function. These findings could have important implications for the molecular diagnosis in patients with isolated SMCP and/or unexplained choanal atresia.

Analysis of transgenic zebrafish expressing the Lenz-Majewski syndrome gene PTDSS1 in skeletal cell lineages.

Background: Lenz-Majewski syndrome (LMS) is characterized by osteosclerosis and hyperostosis of skull, vertebrae and tubular bones as well as craniofacial, dental, cutaneous, and digit abnormalities. We previously found that LMS is caused by de novo dominant missense mutations in the  PTDSS1 gene, which encodes phosphatidylserine synthase 1 (PSS1), an enzyme that catalyses the conversion of phosphatidylcholine to phosphatidylserine. The mutations causing LMS result in a gain-of-function, leading to increased enzyme activity and blocking end-product inhibition of PSS1. Methods: Here, we have used transpose-mediated transgenesis to attempt to stably express wild-type and mutant forms of human PTDSS1 ubiquitously or specifically in chondrocytes, osteoblasts or osteoclasts in zebrafish. Results: We report multiple genomic integration sites for each of 8 different transgenes. While we confirmed that the ubiquitously driven transgene constructs were functional in terms of driving gene expression following transient transfection in HeLa cells, and that all lines exhibited expression of a heart-specific cistron within the transgene, we failed to detect PTDSS1 gene expression at either the RNA or protein levels in zebrafish. All wild-type and mutant transgenic lines of zebrafish exhibited mild scoliosis with variable incomplete penetrance which was never observed in non-transgenic animals. Conclusions: Collectively the data suggest that the transgenes are silenced, that animals with integrations that escape silencing are not viable, or that other technical factors prevent transgene expression. In conclusion, the incomplete penetrance of the phenotype and the lack of a matched transgenic control model precludes further meaningful investigations of these transgenic lines.

Genetics of cleft lip and palate: syndromic genes contribute to the incidence of non-syndromic clefts.

Clefts of the lip and/or palate (CL/P) are among the most common birth defects worldwide. The majority are non-syndromic where CL/P occurs in isolation of other phenotypes. Where one or more additional features are involved, clefts are referred to as syndromic. Collectively CL/P has a major clinical impact requiring surgical, dental, orthodontic, speech, hearing and psychological treatments or therapies throughout childhood. The etiology of CL/P is complex and thought to involve both major and minor genetic influences with variable interactions from environmental factors. Using a combination of gene targeting technology and traditional developmental techniques in both mouse and chick, significant progress has been made in the identification of numerous genes and gene pathways critical for craniofacial development. Despite this, it has been a particular source of frustration that mutation screening of specific candidates, association studies and even genome-wide scans have largely failed to reveal the molecular basis of human clefting. Nevertheless, some important findings have recently come from studies involving syndromic forms of the disorder. These include several genes which have now been shown to contribute a major effect on the etiology of CL/P. Furthermore, these genes can also be used to demonstrate a significant overlap between syndromic and non-syndromic CL/P. The study of these syndromic genes and their molecular pathways will provide a useful and informative route with which to gain a better understanding of human craniofacial pathology.

Craniofacial expression of human and murine TBX22 correlates with the cleft palate and ankyloglossia phenotype observed in CPX patients.

Cleft palate with ankyloglossia (CPX; MIM 303400) is inherited as a Mendelian, semidominant X-linked disorder and has been described in several large families from different ethnic origins. It is a useful genetic model for non-syndromic cleft palate, a common congenital disorder. Recently, the underlying genetic defect in CPX was identified, where unique mutations were found in the T-box-containing transcription factor TBX22. Here we report two new familial cases with novel missense and insertion mutations, each occurring within the T-box domain and highlighting the functional significance of this DNA-binding motif. We describe TBX22 expression in early human development, where expression is found in the palatal shelves and is highest prior to elevation to a horizontal position above the tongue. mRNA is also detected in the base of the tongue in the region of the frenulum that corresponds to the ankyloglossia seen in CPX patients. Other sites of expression include the inferior portion of the nasal septum that fuses to the palatal shelves, the mesenchyme from which tooth buds develop, and the tooth buds themselves. We have also identified the orthologous mouse Tbx22 gene and performed expression analysis in E12.5-E17.5 mouse embryos. The location of mRNA expression closely correlates between mouse and human, while at later stages of development, we also detected expression in mouse lung and whisker follicles. We conclude that expression of TBX22 is entirely consistent with the CPX phenotype and that the mouse should provide a useful model for elucidating its role in craniofacial development.