Revision of Failed Sacroiliac Joint Posterior Interpositional Structural Allograft Stabilization with Lateral Porous Titanium Implants: A Multicenter Case Series.

Background: Distraction arthrodesis (DA) and stabilization of the sacroiliac (SI) joint by placing standalone structural allograft (SA) into the joint from a posterior trajectory has recently been introduced as a surgical procedure for chronic SI joint pain refractory to non-operative care. Methods: Retrospective case series of patients with recurrent and/or persistent pain after placement of one or more interpositional/intraarticular standalone SAs between the ilium and sacrum using a posterior procedure to treat SI joint pain/dysfunction. Patients subsequently underwent surgical revision with porous titanium fusion implants using a lateral transfixing procedure. The demographic, clinical, and radiographic features of these cases are described. Results: Data were available for 37 patients. The average (SD) age was 57 (13) years, 62% were female, and the average BMI was 31 (5.4). On average, two SA implants were placed per joint; 46% of cases were bilateral. At follow-up, two common themes were identified: lucencies around the implants and suboptimal implant position. None of the cases showed radiographic fusion of the SI joint prior to revision. One patient had an inflammatory reaction to the SA. All patients presented for revision due to either continued (49%) or recurrence (51%) of pain. In one revision case, the SA was forced ventrally, resulting in a sacral fracture, which was treated conservatively without sequelae. Conclusions: The popularity of standalone SA for SI joint stabilization/fusion with a posterior procedure is increasing. This case series demonstrates that clinical failures from this procedure may require surgical revision. The proposed fusion strategy (DA) for these products is unproven in the SI joint, and, therefore, properly conducted prospective randomized clinical trials with long-term clinical and radiographic follow-up are important to establish the safety and efficacy of this approach. In the meantime, the placement of lateral titanium implants appears to be an effective revision strategy.

Frederick Sanger, Erwin Chargaff, and the metamorphosis of specificity.

That a transformation of ruling ideas in genetics and biochemistry took place at the dawn of molecular biology, in the late 1940s, is a commonplace; but the nature and components of that transformation are widely misunderstood. The change is often identified with the importation into biology of new styles of thought and new rigor by the many scientists trained in physics or chemistry who came into the nascent field--notably, Max Delbrück, Max Perutz, Francis Crick, John Kendrew, Maurice Wilkins, Rosalind Franklin. Most generally, the change is supposed to be the realization that genes are made not of protein but of nucleic acid--and this change was initiated, of course, by the work of Oswald Avery and his colleagues. These changes are not mutually exclusive, and both were surely important to the genesis of molecular biology. But logically prior to them, more fundamental, was another transformation in ruling preconceptions, one that has been neglected: the revolution in understanding of the chemical structures--the sequences of subunits--of proteins and of nucleic acids which was wrought by the work of Frederick Sanger and of Erwin Chargaff. This was a metamorphosis in the understanding of biochemical specificity, and while it astonished many biochemists it set free the small groups of those who were beginning to call themselves molecular biologists, enabling them to think of the relationship between genes and proteins in entirely new ways.

Lack of involvement of known DNA methyltransferases in familial hydatidiform mole implies the involvement of other factors in establishment of imprinting in the human female germline.

BACKGROUND: Differential methylation of the two alleles is a hallmark of imprinted genes. Correspondingly, loss of DNA methyltransferase function results in aberrant imprinting and abnormal post-fertilization development. In the mouse, mutations of the oocyte-specific isoform of the DNA methyltransferase Dnmt1 (Dnmt1o) and of the methyltransferase-like Dnmt3L gene result in specific failures of imprint establishment or maintenance, at multiple loci. We have previously shown in humans that an analogous inherited failure to establish imprinting at multiple loci in the female germline underlies a rare phenotype of recurrent hydatidiform mole. RESULTS: We have identified a human homologue of the murine Dnmt1o and assessed its pattern of expression. Human DNMT1o mRNA is detectable in mature oocytes and early fertilized embryos but not in any somatic tissues analysed. The somatic isoform of DNMT1 mRNA, in contrast, is not detectable in human oocytes. In the previously-described family with multi-locus imprinting failure, mutation of DNMT1o and of the other known members of this gene family has been excluded. CONCLUSIONS: Mutation of the known DNMT genes does not underlie familial hydatidiform mole, at least in the family under study. This suggests that trans-acting factors other than the known methyltransferases are required for imprint establishment in humans, a concept that has indirect support from recent biochemical studies of DNMT3L.

Relationship between point gene mutation, chromosomal abnormality, and tumour suppressor gene methylation status in colorectal adenomas.

Epigenetic mechanisms in carcinogenesis may have a significant role in the development of colorectal cancer. To investigate this phenomenon in early-stage disease, promoter methylation status in the tumour suppressor genes APC, MGMT, hMLH1, P14/P14ARF, and CDKN2A/P16 was investigated in 78 colorectal adenomas. These had previously been characterized for mutations of APC, KRAS, and TP53 genes and for chromosomal abnormality by comparative genomic hybridization (CGH). APC hypermethylation was seen in 52 tumours (66.7%). APC showed either methylation or mutation in 66 lesions (84.6%), but these events were not statistically associated. MGMT methylation was detected in 39 cases (50%). Adenomas with this abnormality showed a significantly lower number of chromosomal changes by CGH (p < 0.02), confirming that DNA repair defect of this type is associated with a lower level of chromosomal instability. An hMLH1 methylation defect was seen in only one adenoma (1.3%), from a patient who had a synchronous cancer showing the same defect. Methylation of P14 (P14ARF) was seen in 31 adenomas (39.7%) and CDKN2A (P16) abnormality in 25 (32.1%). DNA methylation at two or more loci was seen in 46 tumours (59%), while 11 lesions (14.1%) showed no evidence of hypermethylation at any of the loci studied. Methylation at any or all of MGMT, P14 or P16 was significantly associated with APC methylation (p = 0.01). Those neoplasms with more than two methylated genes showed significantly fewer chromosomal abnormalities than adenomas with one or no methylated loci (p < 0.001). There was no association between specific individual chromosomal abnormalities, APC, KRAS or TP53 mutations and any pattern of methylation abnormality. We conclude that methylation abnormality is very common in pre-invasive colorectal neoplasia, and that high level methylation is associated with low level chromosomal instability.

Structure and mutation analysis of the gene encoding DNA fragmentation factor 40 (caspase-activated nuclease), a candidate neuroblastoma tumour suppressor gene.

We have characterised the DFFB gene, encoding the active subunit of the apoptotic nuclease DNA fragmentation factor (DFF40). DFFB maps to 1p36, near the imprinted putative tumour suppressor gene TP73. The DFFA gene (encoding the inhibitory DFF45 subunit) also maps to 1p36.2-36.3, and we show by FISH that DFFB lies distal to DFFA. We have also mapped a processed DFFB pseudogene to chromosome 9. DFFB itself has seven coding exons spanning 10 kb. Exhaustive mutation screening of 41 neuroblastomas and other tumours in which a 1p36 tumour suppressor gene is implicated showed no tumour-specific mutations. A coding region polymorphism was used to demonstrate uniformly biallelic expression in human fetal DFFB transcripts. Since the putative neuroblastoma tumour suppressor gene in distal 1p36 is predicted to be maternally expressed, the lack of imprinting and absence of somatic mutations in DFFB indicate that it is probably not the neuroblastoma tumour suppressor gene.

The cell cycle control gene ZAC/PLAGL1 is imprinted--a strong candidate gene for transient neonatal diabetes.

We describe a screen for new imprinted human genes, and the identification in this way of ZAC (zinc finger protein which regulates apoptosis and cell cycle arrest)/ PLAGL1 (pleomorphicadenoma of the salivary gland gene like 1) as a strong candidate gene for transient neonatal diabetes mellitus (TNDM). To screen for imprinted genes, we compared parthenogenetic DNA from the chimeric patient FD and androgenetic DNA from hydatidiform mole, using restriction landmark genome scanning for methylation. This resulted in identification of two novel imprinted loci, one of which (NV149) we mapped to the TNDM region of 6q24. From analysis of the corresponding genomic region, it was determined that NV149 lies approximately 60 kb upstream of the ZAC / PLAGL1 gene. RT-PCR analysis was used to confirm that this ZAC / PLAGL1 is expressed only from the paternal allele in a variety of tissues. TNDM is known to result from upregulation of a paternally expressed gene on chromosome 6q24. The paternal expression, map position and known biological properties of ZAC / PLAGL1 make it highly likely that it is the TNDM gene. In particular, ZAC / PLAGL1 is a transcriptional regulator of the type 1 receptor for pituitary adenylate cyclase-activating polypeptide, which is the most potent known insulin secretagog and an important mediator of autocrine control of insulin secretion in the pancreatic islet.