Ossification centre of the hyoid bone in DiGeorge syndrome and tetralogy of Fallot

The Mandibular and Hyoid Arches-From Molecular Patterning to Shaping Bone and Cartilage

The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skeletogenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogenesis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the viscerocranium. In conclusion, we notice that mandibular malformations in humans and mice often co-occur with hyoid malformations and pinpoint the similar molecular machinery controlling the development of mandibular and hyoid arches.

Loss of Tbx1 induces bone phenotypes similar to cleidocranial dysplasia

T-box transcription factor, TBX1, is the major candidate gene for 22q11.2 deletion syndrome (DiGeorge/ Velo-cardio-facial syndrome) characterized by facial defects, thymus hypoplasia, cardiovascular anomalies and cleft palates. Here, we report that the loss of Tbx1 in mouse (Tbx1(-/-)) results in skeletal abnormalities similar to those of cleidocranial dysplasia (CCD) in humans, which is an autosomal-dominant skeletal disease caused by mutations in RUNX2. Tbx1(-/-) mice display short stature, absence of hyoid bone, failed closure of fontanelle, bifid xiphoid process and hypoplasia of clavicle and zygomatic arch. A cell-type-specific deletion of Tbx1 in osteochondro-progenitor (Tbx1(OPKO)) or mesodermal (Tbx1(MKO)) lineage partially recapitulates the Tbx1(-/-) bone phenotypes. Although Tbx1 expression has not been previously reported in neural crest, inactivation of Tbx1 in the neural crest lineage (Tbx1(NCKO)) leads to an absence of the body of hyoid bone and postnatal lethality, indicating an unanticipated role of Tbx1 in neural crest development. Indeed, Tbx1 is expressed in the neural crest-derived hyoid bone primordium, in addition to mesoderm-derived osteochondral progenitors. Ablation of Tbx1 affected Runx2 expression in calvarial bones and overexpression of Tbx1 induced Runx2 expression in vitro. Taken together, our current studies reveal that Tbx1 is required for mesoderm- and neural crest-derived osteoblast differentiation and normal skeletal development. TBX1 mutation could lead to CCD-like bone phenotypes in human.

Hyoid bone abnormalities in Pierre Robin patients

Hyoid bone abnormalities have not been previously documented in association with Pierre Robin Sequence. Using three-dimensional (3D) reconstructions of helical computed tomography scans, we examined the hyoid bones of neonates affected with Pierre Robin Sequence and compared them to helical scans of unaffected controls. Severe hyoid bone abnormalities were observed in 7/28 cases, and mild abnormalities in another 16. The presence of severe abnormalities was significantly associated with swallowing dysfunction, while none of the neonates affected with Stickler's syndrome were observed to have severe hyoid abnormalities. The significance of these findings is unknown. Clinicians should be aware of these abnormalities because of the wide availability of 3D reformats.

Craniofacial cephalometric morphology in children with CATCH 22 syndrome

OBJECTIVES

To evaluate cephalometrically the craniofacial, pharyngeal and cervical morphology in children with CATCH 22, and to compare and quantify the findings with age- and sex-matched controls.

DESIGN

A retrospective case-control study.

SETTING AND SAMPLE POPULATION

Forty-one children (20 girls) with CATCH 22 were compared with age- and sex-matched controls from lateral cephalograms taken at the mean age of 8.5 years (range 5.8-12.9). The deletion of 22q11 was verified by fluorescence in situ hybridization techniques. Thirteen of the children with CATCH 22 had palatal clefts.

OUTCOME MEASURE

Linear and angular measurements were obtained from lateral cephalograms. A Student's t-test and a paired Student's t-test were used in the statistical analysis. Standard deviation scores (SDS) were calculated to quantify the variation.

RESULTS

Children with CATCH 22 had obtuse cranial base angles and long anterior cranial bases. Their faces were long with increased facial convexity. The maxillae were long but both jaws were retrognathic and the lower jaws posteriorly diverged. The pharynges were wide in the nasopharyngeal area and narrow in the hypopharyngeal area. The development of the hyoid bones was delayed, and hyoid bone and atlas lengths were reduced. The morphology of the children with CATCH 22 with and without a palatal cleft was similar. Despite several statistically significant differences between the children with CATCH 22 and the controls, the SDS did not exceed +/-2 for any of the measurements.

CONCLUSION

Children with CATCH 22 have several minor distinctive morphological features in the craniofacial, pharyngeal, and cervical areas.

The hyoid bone in malay infants with cleft lip and palate

OBJECTIVE

To compare morphological and positional variations of the hyoid bone in unoperated infants with cleft lip and palate (CL/P) with those in noncleft infants.

DESIGN

Retrospective, cross sectional.

PATIENTS AND METHODS

Three-dimensional computed tomography scans were obtained from 29 unoperated CL/P infants of Malay origin aged between 0 and 12 months and from 12 noncleft infants in the same age range. Observations were made and measurements were obtained with a software package developed at the Australian Craniofacial Unit. The sizes of the hyoid bones and the position of the hyoid body and epiglottis in relation to the cervical spine were measured. Anatomical anomalies of the hyoid and prevalence of aspiration pneumonia were also documented.

RESULTS

The hyoid bones and epiglottis were found to be located more inferiorly in CL/P infants compared with the noncleft infants. Also, 17% (5/29) of the CL/P infants had nonossified hyoid bodies.

CONCLUSION

The results suggest that there are differences in the location and genesis of the hyoid bone in infants with CL/P that warrant further investigation.

Transplantation of thymus tissue in complete DiGeorge syndrome

BACKGROUND

The DiGeorge syndrome is a congenital disorder that affects the heart, parathyroid glands, and thymus. In complete DiGeorge syndrome, patients have severely reduced T-cell function.

METHODS

We treated five infants (age, one to four months) with complete DiGeorge syndrome by transplantation of cultured postnatal thymus tissue. Follow-up evaluations included immune phenotyping and proliferative studies of peripheral-blood mononuclear cells plus biopsy of the thymus allograft. Thymic production of new T cells was assessed in peripheral blood by tests for T-cell-receptor recombination excision circles, which are formed from excised DNA during the rearrangement of T-cell-receptor genes.

RESULTS

After the transplantation of thymus tissue, T-cell proliferative responses to mitogens developed in four of the five patients. Two of the patients survived with restoration of immune function; three patients died from infection or abnormalities unrelated to transplantation. Biopsies of grafted thymus in the surviving patients showed normal morphologic features and active T-cell production. In three patients, donor T cells could be detected about four weeks after transplantation, although there was no evidence of graft-versus-host disease on biopsy or at autopsy. In one patient, the T-cell development within the graft was demonstrated to accompany the appearance of recently developed T cells in the periphery and coincided with the onset of normal T-cell function. In one patient, there was evidence of thymus function and CD45RA+CD62L+ T cells more than five years after transplantation.

CONCLUSIONS

In some infants with profound immunodeficiency and complete DiGeorge syndrome, the transplantation of thymus tissue can restore normal immune function. Early thymus transplantation - before the development of infectious complications - may promote successful immune reconstitution.

Tracheobronchial anomalies in children with congenital cardiac disease

OBJECTIVE

To perform preoperative airway evaluations, using radiographic analysis, to review the tracheal anatomy in children with congenital cardiac disease.

DESIGN

Prospective.

SETTING

A university children's hospital.

PARTICIPANTS

One hundred patients.

MEASUREMENTS AND MAIN RESULTS

One magnified airway film (high kilovoltage filtered) was performed preoperatively on 100 consecutive children presenting for repair of congenital cardiac disease. Events at intubation, with respect to endotracheal tube size (internal diameter in millimeters) and difficulties with placement of the tube, were recorded. Postoperative morbidity, specifically related to underlying airway anomaly, was documented. Eleven children had positive radiographic findings after review of magnified airway films. Six of 11 patients had evidence of tracheobronchial pathology, and five patients had no tracheal pathology. Difficulties with intubation were noted in two children. No perioperative morbidity was noted in any patient.

CONCLUSION

The use of preoperative magnified airway films for tracheal evaluations in children with cardiac disease should be considered.

The association of tracheal anomalies and tetralogy of Fallot

OBJECTIVE

To determine the incidence of tracheal anomalies in children with tetralogy of Fallot.

DESIGN

Retrospective.

SETTING

A university children's hospital.

PARTICIPANTS

Forty-four children with the diagnosis of tetralogy of Fallot who underwent either primary or palliative cardiac surgery.

MEASUREMENTS AND MAIN RESULTS

Three criteria were used to identify tracheal abnormalities: (1) direct laryngoscopic evidence; (2) radiographic evidence; and/or (3) inability to intubate the trachea with an endotracheal (ET) tube of appropriate size for age, followed by insertion of a 2.5-mm ET tube. An 11% incidence (5/44) of tracheal anomalies was noted. These could be separated into two categories: isolated upper airway pathology (either glottic or subglottic stenosis) and lower tracheal pathology. None of the five children identified with tracheal abnormalities manifested any preoperative signs or symptoms suggestive of airway problems. Four of the children experienced significant perioperative complications resulting directly from the underlying tracheal pathology. This represented a 9% morbidity (4/44) for patients presenting for repair of tetralogy of Fallot.

CONCLUSIONS

A significant incidence of tracheal anomalies is associated with tetralogy of Fallot, leading to potential perioperative complications.

Evaluation of immunity

Immunodeficiency disease is rapidly increasing in frequency. The AIDS epidemic, the increasing use of transplantation with immunosuppression, the aggressive immunotherapy, the persistent deficiencies after bone marrow transplantation--all contribute to the astronomically increasing numbers of patients with host defense failure. This review has presented my viewpoint as to the approaches which can be utilized by practitioners with varying focal points to provide diagnosis and maximize the potential for a cure today or at least to provide the beginnings of understanding from which will come the cures of tomorrow.

Embryologic and other developmental considerations of thirty-eight possible variants of the DiGeorge anomaly

The DiGeorge anomaly (DGA) represents a polytopic developmental field defect that can be caused by a number of different chromosomal, mendelian, toxic, or metabolic factors operating in early embryonic life. If the affected field is thought to be focused on either the fourth branchial arch or the third branchial pouch, with variable cephalad or caudad extension, 38 different combinations of malformations can include DiGeorge anomalies, 24 complete and 14 partial DGA, with the constraints that the field defect must be contiguous (involvement of more than one branchial arch or pouch requires involvement of all intervening arches or pouches) and complete (all derivatives of an affected branchial arch or pouch are deficient). The types and relative frequencies of abnormalities of structures other than the thymus and parathyroid glands in these possible "subsets" of DGA are discussed, and the need for more data on their occurrence in patients diagnosed as having DGA is emphasized.

Ossification centre of the hyoid bone in complete transposition of great vessels, Ivemark asplenia syndrome, and Down's syndrome with congenital heart disease: correlation with the humeral capital epiphysis

The incidence of radiographic visibility of the ossification centres of the body of the hyoid bone and of the humeral capital epiphysis in antero-posterior or lateral chest radiographs taken during the first month of life of 63 autopsied infants were analysed. The group comprised patients with Down's syndrome (DS) with congenital heart disease, 15; complete transposition of the great vessels (TGV), 10; Ivemark asplenia syndrome (IS), 17; and a control group of infants with congenital heart disease (CHD) who had none of the above conditions, nor tetralogy of Fallot, interrupted aortic arch, DiGeorge syndrome or hypoplastic left-heart complex, 31. The incidence of radiographically visible hyoid ossification centre (HOC) in the control group was 71% and of humeral capital epiphysis (HE), 16.1%. Autopsied infants with TGV, IS or DS with CHD showed increased visibility of HOC (100%); the incidence of visible HE was increased in neonates with IS (71.4%) and with TGV (50%). The differences in the incidence of radiographic visibility of HOC and HE in neonates with CHD, in this study and in others in the literature, appear to have diagnostic value.