The vascularized pig fibula bone flap model: effect of segmental osteotomies and internal fixation on blood flow.

The free fibular flap is the flap of choice for reconstruction of complex mandibular defects, although two or more osteotomies may be required to recreate the normal mandibular contour. The effect of these surgical manipulations on the fibula has not been adequately investigated. This study was designed to study the effect of multiple segmental osteotomies and internal fixation techniques on blood flow in the vascularized pig fibula bone flap model. The hindlimbs of 15 Yorkshire pigs were randomized into 1 of 5 groups (n = 6 fibulae per group) consisting of: (1) a nonoperated, in situ fibula; (2) an elevated fibula flap; (3) an elevated fibula flap with two segmental osteotomies; (4) an elevated fibula with two segmental closing osteotomies rigidly fixed with 2-mm miniplates; (5) an elevated fibula with two segmental closing osteotomies rigidly fixed with 2-mm lag screws. Total and gradient blood flow was measured in the bone and soft-tissue components of these flaps using the 15-microm radioactive microsphere technique. The creation of two segmental osteotomies in the vascularized pig fibula bone flap model resulted in a significant decrease (p<0.05) in the gradient blood flow in the segment of bone distal to the second osteotomy. Application of miniplates or lag screws across closing osteotomies resulted in a significant decrease (p<0.05) in total and gradient blood flow to the bone component of the fibulae, as compared with the elevated and osteotomized fibulae groups. An increase in blood flow suggesting a hyperemic response was noted in the bone and soft tissue in the elevated and osteotomized flap groups as compared with the in situ, nonoperated controls. This study established the validity of the pig fibula as a suitable model for investigating the pathophysiology of blood flow changes in the face of standard surgical maneuvers necessary for the restoration of mandibular form and function. The results demonstrated that the creation of multiple segmental osteotomies and the application of internal fixation significantly decreases (p<0.05) blood flow to the distal portion of the flap. The effects of segmental osteotomies and internal fixation on healing and growth of the pig fibula bone flap model are investigated in a separate study.

Aortic dissection, patent ductus arteriosus, iris hypoplasia and brachytelephalangy in a male adolescent.

We describe a 14-year-old male with dissection of the descending aorta, bilateral iris hypoplasia, striae distensae and brachytelephalangy, the latter being most marked in the thumbs. Inguinal herniae and a patent ductus arteriosus were surgically repaired in infancy. The pattern of abnormalities may constitute a previously undescribed syndrome. The proband died suddenly at the age of 17 years.

Desferrioxamine ototoxicity in an adult transfusion-dependent population.

OBJECTIVE: The purpose of this study was to identify the incidence of hearing loss in a population of 75 adult (19-68 years old) transfusion-dependent patients with thalassemia major, sickle cell disease, Diamond-Blackfan anemia, and various other hematologic disorders treated with regular transfusion schedules. Ninety-three percent (70/75) of patients had a history of long-term subcutaneous or intravenous desferrioxamine therapy. METHODS: The patients underwent routine otolaryngologic history and physical examination, along with standard pure-tone audiometry at 250, 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz, with hearing loss defined as 25 dB or greater at one or more frequencies. RESULTS: Hearing loss was present in 57% (43/75) of patients. More importantly, hearing loss attributable to desferrioxamine ototoxicity was present in 29% (22/75) of patients. Sixteen patients treated previously with desferrioxamine were switched to the experimental oral chelating agent, L1. Eight of these 16 patients had hearing loss attributable to desferrioxamine, with 5 of these patients worsening with the experimental oral chelating agent L1. Seventy-nine percent (59/75) of patients were thalassemic. Fifty-four percent (33/59) of these thalassemic patients had hearing loss. However, 35% (21/59) of the thalassemic patients had hearing loss attributable to desferrioxamine ototoxicity. All thalassemic patients with desferrioxamine ototoxicity had high-frequency sensorineural hearing loss, with 33% (7/21) having a notch at 6 kHz. In addition, 5% (1/21) had notching at 3 khz. Few of the hearing losses were disabling. CONCLUSIONS: Management of these patients requires proper dosing of desferrioxamine and transfusion therapy, along with regular monitoring of body iron burden and hemoglobin. In addition, regular otolaryngologic and audiometric follow-up with special care to include the frequencies of 3 and 6 kHz may help recognize and prevent permanent ototoxicity.

Anatomic and hemodynamic study of the vascularized pig fibula bone flap model.

Despite much interest in studying the pathophysiology of experimental skin and muscle flaps to better understand the pathobiology of flap failure, relatively little has been published in the investigation of vascularized bone flaps. The aim of this study was to develop a suitable vascularized bone flap model in the pig in the hope that this model may prove useful in studying the pathophysiology of vascularized bone tissue transfer. Yorkshire pigs (17-26 kg) were used for all experiments. Anatomic studies revealed that the fibula in the hindlimb was the most suitable bone for investigation as a flap model. Anatomic dissections, radiologic investigations (plain x-rays, angiograms), and morphometric analyses of the fibulae in both hindlimbs of five animals were carried out. In a separate group of pigs (n = 6), the fibula was elevated as a vascularized flap and then blood flow was measured using the 15-microns radioactive microsphere technique. The fibula in the pig is supplied by a branch of the cranial tibial artery, running along an intermuscular septum between the posterior and anterior compartments of the hindlimb accompanied by one or two vena commitans. The bone flap is raised with a cuff of flexor hallucis longus with a length of 9.2 +/- 0.2 cm (mean +/- SEM). Blood flow measurement confirmed that the entire fibula was well vascularized when elevated on its pedicle. Gradient blood flow showed a bimodal distribution, with regions of highest blood flow noted at the proximal and distal ends of the bone flap, in areas where there were greater percentages of cancellous bone. The results of these experiments suggest that the pig fibula may be a suitable model for the study of vascularized bone flap pathophysiology.

Abnormal type III collagen produced by an exon-17-skipping mutation of the COL3A1 gene in Ehlers-Danlos syndrome type IV is not incorporated into the extracellular matrix.

A novel heterozygous mutation of the COL3A1 gene that encodes the alpha 1(III) chains of type III collagen was identified in a family with the acrogeric form of Ehlers-Danlos syndrome type IV (EDS-IV). Cultured dermal fibroblasts produced normal and shortened alpha 1(III) chains. The triple helix of the latter chain was shortened owing to a 33 amino acid deletion of Gly-184 to Pro-216. The corresponding region of cDNA lacked 99 base pairs from nucleotides 1051 to 1149. The deletions corresponded exactly to the normal sequence encoded by exon 17 of the COL3A1 gene. The proband was heterozygous for a T to G transversion at position +2 of intron 17, which resulted in skipping of exon 17. The splicing defect was not corrected by growing the fibroblasts at 33 degrees C and no other splicing variants were identified at 33 or 37 degrees C. The affected brother had the same mutation but his unaffected mother did not. Heterotrimeric type III collagen molecules containing normal and mutant chains were retained within the cell. The mutant homotrimeric molecules were modified and secreted normally and were thermally stable. These normal characteristics of the mutant homotrimers suggested that the loss of ten Gly-Xaa-Yaa triplets (where Gly-Xaa-Yaa is a repetitive amino acid triplet structure in which Xaa and Yaa are other amino acids, proline and hydroxyproline being more common in the Yaa position) did not adversely affect the formation and stability of the triple helix or the structural requirements for secretion. However, the mutant homotrimers were not incorporated into the extracellular matrix of an in vitro model of EDS-IV dermis. The EDS-IV phenotype in this family was probably due to a deficiency in the amount of normal type III collagen available for formation of the heterotypic collagen fibrils of the extracellular matrix. Intracellular and extracellular quality-control mechanisms prevented the incorporation of heterotrimeric and homotrimeric mutant type III collagen molecules into the cross-linked extracellular matrix.

Myocardial infarction resulting from coronary artery dissection in an adolescent with Ehlers-Danlos syndrome type IV due to a type III collagen mutation.

Ehlers-Danlos syndrome encompasses a group of inherited disorders of connective tissue, some of which are characterised by abnormalities of collagen metabolism. The chromosomal location, identified genes and biochemical defects, inheritance pattern, and clinical features for the various known subtypes are outlined. Prenatal diagnosis is possible for types IV, VI, VIIA1, and VIIA2. An unusual presentation of type IV Ehlers-Danlos syndrome in a 16 year old boy with an anterior myocardial infarction resulting from dissection of the left anterior descending coronary artery is reported here. A clinical diagnosis of type IV Ehlers-Danlos syndrome was made subsequently and confirmed by the reduced production, impaired secretion, and abnormally slow electrophoretic migration of type III collagen, indicating an underlying mutation in the COL3A1 gene. This patient represents the first case of type IV Ehlers-Danlos syndrome with symptomatic coronary artery dissection.

The clinical features of Ehlers-Danlos syndrome type VIIB resulting from a base substitution at the splice acceptor site of intron 5 of the COL1A2 gene.

The features of a 32 year old woman with Ehlers-Danlos syndrome type VIIB and affected members of her family, resulting from a mutation in one COL1A2 allele, were studied. Her dermal type I collagen contained alpha 2(I) chains and mutant pN-alpha 2(I) chains in which the amino-terminal propeptide remained attached to the alpha 2(I) chain. She was heterozygous for an AG-->AC mutation at the splice acceptor site of intron 5 of the COL1A2 gene. The mutation activated a cryptic AG splice acceptor site corresponding to positions +14 and +15 of exon 6 of the COL1A2 gene. In contrast to previous reports only five, rather than all 18, amino acids encoded by exon 6 were deleted in the proband. The deleted peptide removed the amino-proteinase cleavage site, but not the nearby lysine cross linking site in the amino-telopeptide of the alpha 2(I) chain. She was born with bilateral hip dislocations, knee subluxations, and generalised joint hypermobility. Bilateral inguinal herniae and an umbilical hernia were present at birth. Facial features included a depressed nasal bridge with prominent paranasal folds. The skin was soft, moderately hyperelastic, and sagged over the face. Skin fragility and easy bruising were apparent from childhood. Skin wounds healed slowly and with broad, paper thin scars. Throughout her life, she had multiple fractures of the small bones of her hands and feet following moderate trauma. Electron microscopy of the proband's dermis as well as deep fascia and hip joint capsule from her affected brother showed that collagen fibrils in transverse section were nearly circular but with irregular margins. Light microscopy of bone from her affected brother and son showed normal Haversian systems and lamellar bone. All of these tissues contained approximately equal amounts of the normal and mutant alpha2(I) chains. The findings of this study confirm that loss of the amino-proteinase cleavage site of the pro alpha2(I) collagen chains, owing to anomalous splicing of exon 6 sequences in the conversion of pre-mRNA to mRNA, produces the clinical features of Ehlers-Danlos syndrome type VIIB. The history of frequent fractures found in this family is atypical and indicates an overlap with osteogenesis imperfecta.

Experimental, clinical and preventive aspects of ototoxicity.

Ototoxicity is an important clinical problem and accounts for a significant proportion of sensorineural hearing loss in some parts of the world. Ototoxicity is predominantly an iatrogenic condition. However, with proper dosing, prudent monitoring of serum levels of ototoxic medications and serial audiometry, ototoxicity can be prevented. A number of the more common ototoxic medications, including aminoglycosides, erythromycin, loop diuretics, salicylates, cisplatin, deferoxamine and ototopical agents, are outlined in this review. Their pharmacology, mechanisms of action and methods of preventing complications are discussed together with animal and clinical studies.

A base substitution at the splice acceptor site of intron 5 of the COL1A2 gene activates a cryptic splice site within exon 6 and generates abnormal type I procollagen in a patient with Ehlers-Danlos syndrome type VII.

The dermal type I collagen of a patient with Ehlers-Danlos type VIIB (EDS-VIIB) contained normal alpha 2(I) chains and mutant pN-alpha 2(I)' chains in which the amino-terminal propeptide (N-propeptide) remained attached to the alpha 2(I) chain. Similar alpha 2(I) chains were produced by cultured dermal fibroblasts. Amino acid sequencing of tryptic peptides, prepared from the mutant amino-terminal pN-alpha 2(I) CB1' peptide, indicated that five amino acids, including the N-proteinase (the specific proteinase that cleaves the procollagen N-propeptide) cleavage site, had been deleted from the junction of the N-propeptide and the N-telopeptide (the nonhelical domain at the amino-terminus of the alpha chains of fully processed type I polypeptide chains) of the mutant pro-alpha 2(I)' chain. The corresponding 15 nucleotides, which were deleted from approximately half of the alpha 2(I) cDNA polymerase chain reaction products, of the alpha 2(I) cDNA polymerase chain reaction products, were encoded by the +1 to +15 nucleotides of exon 6 of the normal alpha 2(I) gene (COL1A2). These 15 nucleotides were deleted in the splicing of alpha 2(I) pre-mRNA to mRNA as a result of inactivation of the 3' splice site of intron 5 by an AG to AC mutation and the activation of a cryptic AG splice acceptor site corresponding to positions +14 and +15 of exon 6. Loss of the N-proteinase cleavage site explained the persistence of the pN-alpha 2(I)' chains in the dermis and in fibroblast cultures. Collagen production by cultured dermal fibroblasts was doubled, possibly due to reduced feedback inhibition by the N-propeptides. In contrast to previously reported cases of EDS-VIIB, Lys5 of the N-telopeptide was not deleted and appeared to take part in the formation of intramolecular cross-linkages. However, increased collagen solubility and abnormal extraction profiles of the mutant type I collagen molecules indicated that collagen cross-linking was abnormal in the dermis. The proband and her son were heterozygous for the mutation. It is likely that the heterozygous loss of the N-proteinase cleavage site, with persistence of a shortened N-propeptide, was the major factor responsible for the EDS-VIIB phenotype.

Ehlers-Danlos syndrome type IV: phenotypic consequences of a splicing mutation in one COL3A1 allele.

The features of a child with Ehlers-Danlos syndrome type IV (EDS IV) resulting from a mutation in one COL3A1 allele were studied. The child was heterozygous for a G- to A-transition at the splice donor site of intron 41. It resulted in the splicing out of the exon 41 encoded sequence from alpha 1(III) mRNA and the deletion of 36 amino acids from glycine775 to lysine810 of the triple helical domain of alpha 1(III) chains of type III collagen. The amount of type III collagen in the dermis was only about 11% of normal. The child had the acrogeric form of EDS IV. He had the characteristic facies with a pinched nose, thin lips, and prominent eyes. These facial features, his aesthenic build, thin skin, prominent subcutaneous veins, and aged hands produced a 'cachectic' appearance. These features were evident in early childhood and worsened up to 12 1/2 years when he was last reviewed. Spontaneous bruising, bleeding from the large bowel, constipation, and delayed gastric emptying were other features. In cross section, the dermal collagen fibrils were round and measured 93.3 +/- 11.5 nm in diameter which was not significantly different from control values of 102.5 +/- 13.4 nm. The serum type III procollagen amino-terminal propeptide level of 25.5 ng/ml was within the normal age matched values of 15.5 +/- 7.7 ng/ml despite the low production of type III collagen by cultured fibroblasts. The child probably had a spontaneous new mutation in one COL3A1 allele as only normal sequences were obtained from the corresponding amplified region of the parent's leucocyte DNA.

A base substitution at a splice site in the COL3A1 gene causes exon skipping and generates abnormal type III procollagen in a patient with Ehlers-Danlos syndrome type IV.

The dermis of a child with Ehlers-Danlos syndrome type IV (EDS-IV) contained about 11% of the normal amount of type III collagen and cultured dermal fibroblasts produced a reduced amount of type III procollagen which was secreted poorly. Type III collagen produced by these cells contained normal and abnormal alpha-chains and cyanogen bromide peptides. The site of the structural defect in the abnormal alpha 1 (III) chains was localized to the region of Met797, which is at the junction of the two carboxyl-terminal CB5 and CB9 cyanogen bromide peptides. Chemical cleavage of heteroduplexes formed between EDS-IV mRNA and a normal cDNA clone covering the CB5 and CB9 region showed that about 100 nucleotides were mismatched. Sequencing of amplified and cloned cDNA spanning the mutant region revealed a 108 nucleotide deletion corresponding to amino acid residues Gly775 to Lys810. The deleted nucleotide sequence corresponded to sequences that, by analogy to the organization of the type I collagen genes, should be precisely encoded by exon 41 of the COL3A1 gene. Sequencing of amplified genomic DNA, prepared using disimilar amounts of primers specific for exons 41 and 42, displayed a base substitution (G-to-A) in the highly conserved GT dinucleotide of the 5' splice site of intron 41. Normal sequences were also obtained from the normal allele. It is likely that the GT-to-AT transition at the splice donor site of intron 41 generated an abnormally spliced mRNA in which sequences of exon 40 and 42 were joined together with maintenance of the reading frame. The corresponding peptide deletion included the cyanogen bromide cleavage site Met797-Pro798 and the mammalian collagenase cleavage site at Gly781-Ile782. These losses account for the resistance of EDS-IV collagen to cyanogen bromide and mammalian collagenase digestion. Cultured fibroblasts produced normal homotrimer, mutant homotrimer, and mixed heterotrimer type III collagen molecules. The mutant homotrimer molecules were the major pepsin-resistant species and about 69% of the alpha 1(III) mRNA was in the mutant form.