Molecular genetics and craniofacial surgery

Craniosynostosis

Craniosynostosis is a premature pathologic fusion of one or more cranial vault sutures that leads to abnormal shape of the skull. The fused sutures lead to restricted growth in some areas and compensatory bossing in other areas. The head may assume different shapes depending upon the site and timing of the abnormally fused suture. The exact cause of this suture pathology is still unknown, but the local dura, cranial base and the fibroblast growth factors seem to influence this. The diagnosis rests on clinical examination and confirmation is generally on the computed tomography scan. The need for surgery is both for cosmetic and functional reasons. Many cases may be associated with raised intracranial pressure with its attendant deleterious effects on vision and brain. The aim of treatment is to increase the cranial volume and reshape the skull. The surgery can be safely undertaken around 9-12 months in most of the cases. The conventional management is through an open surgical approach; although, some centres have claimed impressive results with limited endoscopic techniques in selected cases. The review article deals with the aetiopathogenesis, clinical presentations and management of the common varieties of craniosynostoses seen in the Indian scenario.

Modeling of Scaphocephaly Using Superelastic Titanium-Nickel Rings: A Preliminary Report

As long as resection of sagittal suture eliminates craniostenosis it leads to desired cranium broadening and shortening solely in the case of children under six months of age. In the majority of cases, especially in older children, boat-shaped cranium remains rather unchanged and its effective modeling requires extensive dissection and osteotomy of the whole cranium vault (e.g., frontal, occipital and parietal bones). Lauritzen's method is an alternative solution. It consists of distraction of cranium vault bones with the aid of steel springs. In order to simplify and improve the efficacy of treatment since 2002, the authors originated the application of titanium-nickel rings to model the cranium. After the sparing excision of cranium vault sutures in the shape of letter "H" the compressed ring is given in the sagittal axis oval shape and in this form it is fixed to osseous margins. The ring's expansion at the same time broadens and shortens the cranium vault. Material was analyzed from 7 children (range, 9 months to 4 years of age), who were treated in the years 2002-2006 because of sagittal craniostenosis. Observations made so far and good treatment results indicate purposefulness of discussed treatment continuation.

Treatment of Nonsyndromic Bilateral Coronal Synostosis Using a Multiple Bone Flap Rotation-Reposition Technique

Brachycephaly is the result of premature fusion of the bilateral coronal suture. Various surgical procedures have been devised to manage brachycephaly, but there is no standard surgical method in brachycephalic treatment. Suboptimal results may be related to the tendency of misdirected bone growth of the remaining cranium in brachycephaly. Therefore, the abnormal growth vectors should be corrected toward a more normal configuration. Between 1997 and 2001, three nonsyndromic brachycephalic patients were treated using the described procedure. The cranial remodeling procedure used consists of supraorbital bar advancement and the rotation-reposition of multiple frontoparietal bone flaps. The frontoparietal bone was cut into seven segments consisting of two upper frontal, two lower frontal, one anterior parietal (T-shaped), and two posterior parietal segments. Each lower frontal segment was rotated 180 degrees and transposed with the corresponding contralateral upper frontal segment. Each upper frontal segment was then transposed to the upper margin of the supraorbital bar. The posterior margin of the frontal segment was not fixed (floating forehead). Anterior parietal and two posterior parietal segments were trimmed and repositioned to the original position. The postoperative follow-up period ranged from 17 to 52 months (mean = 30 months). The cranial configuration obtained after the operation was considerably improved, approaching a normal shape in all cases. The mean length of frontal advancement was 11 mm (range: 7-15 mm). The preoperative mean value of the cephalic index was markedly raised to 104.7 (range: 100-111). The postoperative (at last follow-up) mean value of the cephalic index was 89.2 (range: 86.3-94.3). A better skull contour could be obtained easily by converting abnormally directed long upward and transverse dimensions to short anteroposteriorly directed dimensions. Cranial remodeling using repositioned multiple bone flaps can produce excellent results functionally and esthetically in brachycephaly.

Management of craniosynostosis

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Review the etiopathogenesis of craniosynostosis and craniofacial anomalies. 2. Develop a basic understanding of the clinical manifestations and diagnosis of craniofacial anomalies. 3. Describe the surgical principles of managing craniosynostosis and craniofacial anomalies.Craniosynostosis, or the premature closure of calvarial sutures, results in deformed calvaria at birth. Although the etiology of craniosynostosis is currently unknown, animal experiments and a recent interest in molecular biology point toward interplay between the dura and the underlying brain. This interaction occurs by means of a local alteration in the expression of transforming growth factor, MSX2, fibroblast growth factor receptor, and TWIST. The fused suture restricts growth of the calvaria, thus leading to a characteristic deformation, each associated with a different type of craniosynostosis. Uncorrected craniosynostosis leads to a continuing progression of the deformity, and in some cases, an elevation of intracranial pressure. Clinical examination should include not only an examination of the skull but also a general examination to rule out the craniofacial syndromes that accompany craniosynostosis. Because deformational plagiocephaly, or plagiocephaly without synostosis, occurs secondary to sleeping in the supine position during the early perinatal period, the physician should be aware of this abnormality. Treatment for deformational plagiocephaly is conservative when compared with treatment for craniosynostosis, which requires surgery. Appropriate investigations should include genetic screening, radiologic examination with a computerized tomographic scan, and neurodevelopmental analysis. Surgical intervention should be performed during infancy, preferably in the first 6 months of postnatal life, to prevent the further progression of the deformity and possible complications associated with increased intracranial pressure. The principles of surgical intervention are not only to excise the fused suture but also to attempt to normalize the calvarial shape. Long-term follow-up is critical to determine the effect of the surgical outcome.

From the chromosome to DNA: Restriction fragment length polymorphism analysis and its clinical application

Understanding how chromosomal alterations contribute to acquired and inherited human disease requires the ability to manage the enormous physical and informational complexity of the deoxyribonucleic acid (DNA) packaged within. Important concepts and techniques involved in the analysis of DNA include restriction enzymes, Southern blotting, and restriction fragment length polymorphism/linkage analysis. These techniques have been essential in the understanding and diagnosis of several syndromes associated with the head and neck. The purpose of this article is to introduce DNA structure, describe some techniques fundamental to DNA analysis, and provide a brief overview of the clinical applications of this technology with respect to dentinogenesis imperfecta and oral field cancerization.

The chromosome: cytogenetic analysis and its clinical application

PURPOSE

Chromosomes are highly structured, dynamic complexes of DNA and protein. The human genome consists of 46 chromosomes (22 paired autosomes and 2 sex chromosomes). Cytogenetic analysis provides a means to identify, as well as describe, chromosomes and disorder-related aberrations. The purpose of this article is to 1) introduce chromosome structure and alterations, 2) describe the technical fundamentals of cytogenetic analysis, and 3) provide a brief overview of the clinical applications of this technology.

Analysis of fronto-orbital advancement for Apert, Crouzon, Pfeiffer, and Saethre-Chotzen syndromes

The purposes of this study were (1) to document outcome after primary fronto-orbital advancement for the four major eponymous craniosynostotic syndromes (Apert, Crouzon, Pfeiffer, and Saethre-Chotzen) and (2) to identify factors that might influence need for primary and secondary fronto-orbital advancement or foreheadplasty. Also tested was the hypothesis that coincident sagittal synostosis could modulate brachycephaly and affect whether a primary or secondary frontal operation was necessary. Data were collected on age and indications for initial operation, type of primary and secondary frontal procedures, and concomitant sagittal synostosis. Patients initially managed by subcranial Le Fort III were included in the study group but excluded from analysis of fronto-orbital advancement. Patients treated by monobloc advancement or Le Fort III osteotomies with frontal grafting or Anderl modification were assessed as having had primary fronto-orbital advancement. Minimum time to follow-up was 5 years. A total of 126 patients met inclusion criteria. Lateral photographs were examined to assess preoperative and postoperative sagittal position of supraorbital rims-to-globes. Frontal re-advancement was indicated if the corneal apex was anterior to the supraorbital rim. Foreheadplasty was indicated for unacceptable frontal contour and normal supraorbital rim-to-globe relationship. Primary correction for frontal retrusion was not required in 4 percent of Apert (1 of 25), 16 percent of Crouzon (7 of 44), 6 percent of Pfeiffer (2 of 31), and 19 percent of Saethre-Chotzen (5 of 26) patients. Of those infants who had a primary fronto-orbital advancement, reoperation for either supraorbital retrusion or frontal deformity was necessary in all 16 Apert patients and in 5 of 19 Crouzon (26 percent), 10 of 26 Pfeiffer (38 percent), and 13 of 20 Saethre-Chotzen (65 percent) patients (p < 0.001). Age at initial fronto-orbital advancement did not influence reoperative rate. No correlation was found between concomitant sagittal synostosis and necessity for primary or secondary frontal correction (p = 0.22). In summary, phenotypic diagnosis was determinant for outcome as defined by need for secondary fronto-orbital advancement, foreheadplasty, or both. Apert patients had the highest incidence of reoperation for frontal retrusion or forehead contour. Crouzon and Saethre-Chotzen patients were most likely to express a minor phenotype and not require fronto-orbital correction. Coincident sagittal synostosis did not influence frontal projection, as reflected in need for either primary or secondary frontal advancement.

Molecular diagnosis of bilateral coronal synostosis

The authors performed a prospective study evaluating molecular diagnosis in patients with bilateral coronal synostosis. The patients were divided into two groups: (1) those clinically classified as having Apert, Crouzon, or Pfeiffer syndrome and (2) those clinically unclassified and labeled as having brachycephaly. Blood samples were drawn for genomic DNA analysis from 57 patients from 1995 to 1997. Polymerase chain reactions were performed using primers flanking exons in FGFR 1, 2, and 3. Each exon was screened for mutations using single-strand confirmation polymorphism, and mutations were identified by DNA sequencing. Mutations in FGFR2 or FGFR3 were found in all patients (n = 38) assigned a phenotypic (eponymous) diagnosis. All Apert syndrome patients (n = 13) carried one of the two known point mutations in exon 7 of FGFR2 (Ser252Trp and Pro253Arg). Twenty-five patients were diagnosed as having either Crouzon or Pfeiffer syndrome. Five patients with Crouzon syndrome of variable severity had mutations in exon 7 of FGFR2. Fifteen patients (12 with Crouzon, 3 with Pfeiffer) had a mutation in exon 9 of FGFR2, many of which involved loss or gain of a cysteine residue. A wide phenotypic range was observed in patients with identical mutations, including those involving cysteine. Two patients labeled as having Crouzon syndrome had the Pro250Arg mutation in exon 7 of FGFR3. All three patients with the crouzonoid phenotype and acanthosis nigricans had the same mutation in exon 10 of FGFR3 (Ala391Glu). This is a distinct disorder, characterized by jugular foraminal stenosis, Chiari I anomaly, and intracranial venous hypertension. Mutations were found in 14 of 19 clinically unclassifiable patients. Three mutations were in exon 9, and one was in the donor splice site of intron 9 on FGFR2. The most common mutation discovered in this group was Pro250Arg in exon 7 of FGFR3. These patients (n = 10) had either bilateral or unilateral coronal synostosis, minimal midfacial hypoplasia with class I or class II occlusion, and minor brachysyndactyly. No mutations in FGFR 1, 2, or 3 were detected in five patients with nonspecific brachycephaly. In conclusion, a molecular diagnosis was possible in all patients (n = 38) given a phenotypic (eponymous) diagnosis. Different phenotypes observed with identical mutations probably resulted from modulation by their genetic background. A molecular diagnosis was made in 74 percent of the 19 unclassified patients in this series; all mutations were in FGFR2 or FGFR3. Our data and those of other investigators suggest that we should begin integrating molecular diagnosis with phenotypic diagnosis of craniosynostoses in studies of natural history and dysmorphology and in analyses of surgical results.

Genetics of limb development and congenital hand malformations

The vertebrate limb bud develops along three different axes: proximodistal, anteroposterior, and dorsoventral. Several genetic factors responsible for control of each of the three limb axes have been identified. The genes involved interact in complex feedback loops to achieve proper arrangement and differentiation of tissues. Most of the available information on limb development and patterning has come from studies carried out in the lower vertebrates. In recent years, an increasing number of studies have been unraveling the genetic basis of human hand malformation phenotypes. At present, genes responsible for preaxial polydactyly, split hand/split foot malformation, and brachydactyly type C have been localized, and the gene responsible for synpolydactyly has been identified. In this paper, we present an overview of the genetic factors involved in limb development, followed by summarized discoveries in the genetics of human congenital hand malformations.

A new in utero sheep model for unilateral coronal craniosynostosis

Several animal models have been designed in the past to analyze the pathophysiology and management of craniosynostosis, very few of which were intrauterine. Those that were interuterine had problems with either a short gestation or limited availability that prevented most researchers from using them in treatment analysis. We desired to create a biologically sound intrauterine model of craniosynostosis, using an animal with a long gestation and an early calvarial bone formation, which was easy to manipulate in utero, that could be created by any researcher studying this disorder. Using biologic data available regarding growth factors thought to be involved in bone growth and cranial suture closure, we developed a new in utero fetal lamb model for the study of craniosynostosis. Ten 70-day gestation fetal lambs (term gestation 140 days) received a midline coronal incision to expose both coronal sutures. The entire right coronal suture was then excised along with a 4-mm bony margin. In each animal, the site was packed with 25 mg of demineralized sheep bone powder augmented with 50 microg of bone morphogenetic protein-2 (BMP-2) and 1 microg of poly-transforming growth factor-beta. The scalp was closed, and the sheep were returned to the uterus until either 90 or 140 days of gestation. Complete fusion of the right coronal suture occurred in all fetuses by 90 days gestation. In every animal, right-sided frontal bone flattening and supraorbital rim elevation were evident. Histologic analysis showed bony synostosis at the suture site without evidence of suture regeneration. By 140 days, this isolated suture fusion led to marked craniofacial abnormalities including right supraorbital rim elevation, significant frontal bone flattening, a decrease in the anterior-posterior length of the cranial vault, and flattening of the cranial base. In conclusion, we have developed a new model for the study of the secondary effects induced by the process of cranial suture fusion, which produces abnormalities seen in naturally occurring cases of isolated right coronal suture synostosis. In addition, this model confirms that isolated coronal suture fusion alone can lead to the multiple cranial and facial abnormalities seen with this disorder, even in the absence of associated cranial base suture fusions.