Altered Sox9 and FGF signaling gene expression in Aga2 OI mice negatively affects linear growth

Osteogenesis imperfecta (OI), or brittle bone disease, is a disorder characterized by bone fragility and increased fracture incidence. All forms of OI also feature short stature, implying an effect on endochondral ossification. Using the Aga2+/- mouse, which has a mutation in type I collagen, we show an affected growth plate primarily due to a shortened proliferative zone. We used single-cell RNA-Seq analysis of tibial and femoral growth plate tissues to understand transcriptional consequences on growth plate cell types. We show that perichondrial cells, which express abundant type I procollagen, and growth plate chondrocytes, which were found to express low amounts of type I procollagen, had ER stress and dysregulation of the same unfolded protein response pathway as previously demonstrated in osteoblasts. Aga2+/- proliferating chondrocytes showed increased FGF and MAPK signaling, findings consistent with accelerated differentiation. There was also increased Sox9 expression throughout the growth plate, which is expected to accelerate early chondrocyte differentiation but reduce late hypertrophic differentiation. These data reveal that mutant type I collagen expression in OI has an impact on the cartilage growth plate. These effects on endochondral ossification indicate that OI is a biologically complex phenotype going beyond its known impacts on bone to negatively affect linear growth.

Expanding the genetic architecture and phenotypic spectrum in the skeletal ciliopathies

Defects in the biosynthesis and/or function of primary cilia cause a spectrum of disorders collectively referred to as ciliopathies. A subset of these disorders is distinguished by profound abnormalities of the skeleton that include a long narrow chest with markedly short ribs, extremely short limbs, and polydactyly. These include the perinatal lethal short-rib polydactyly syndromes (SRPS) and the less severe asphyxiating thoracic dystrophy (ATD), Ellis-van Creveld (EVC) syndrome, and cranioectodermal dysplasia (CED) phenotypes. To identify new genes and define the spectrum of mutations in the skeletal ciliopathies, we analyzed 152 unrelated families with SRPS, ATD, and EVC. Causal variants were discovered in 14 genes in 120 families, including one newly associated gene and two genes previously associated with other ciliopathies. These three genes encode components of three different ciliary complexes; FUZ, which encodes a planar cell polarity complex molecule; TRAF3IP1, which encodes an anterograde ciliary transport protein; and LBR, which encodes a nuclear membrane protein with sterol reductase activity. The results established the molecular basis of SRPS type IV, in which mutations were identified in four different ciliary genes. The data provide systematic insight regarding the genotypes associated with a large cohort of these genetically heterogeneous phenotypes and identified new ciliary components required for normal skeletal development.

MED resulting from recessively inherited mutations in the gene encoding calcium-activated nucleotidase CANT1

Multiple Epiphyseal Dysplasia (MED) is a relatively mild skeletal dysplasia characterized by mild short stature, joint pain, and early-onset osteoarthropathy. Dominantly inherited mutations in COMP, MATN3, COL9A1, COL9A2, and COL9A3, and recessively inherited mutations in SLC26A2, account for the molecular basis of disease in about 80-85% of the cases. In two families with recurrent MED of an unknown molecular basis, we used exome sequencing and candidate gene analysis to identify homozygosity for recessively inherited missense mutations in CANT1, which encodes calcium-activated nucleotidase 1. The MED phenotype is thus allelic to the more severe Desbuquois dysplasia phenotype and the results identify CANT1 as a second locus for recessively inherited MED.

Loss of DDRGK1 modulates SOX9 ubiquitination in spondyloepimetaphyseal dysplasia

Shohat-type spondyloepimetaphyseal dysplasia (SEMD) is a skeletal dysplasia that affects cartilage development. Similar skeletal disorders, such as spondyloepiphyseal dysplasias, are linked to mutations in type II collagen (COL2A1), but the causative gene in SEMD is not known. Here, we have performed whole-exome sequencing to identify a recurrent homozygous c.408+1G>A donor splice site loss-of-function mutation in DDRGK domain containing 1 (DDRGK1) in 4 families affected by SEMD. In zebrafish, ddrgk1 deficiency disrupted craniofacial cartilage development and led to decreased levels of the chondrogenic master transcription factor sox9 and its downstream target, col2a1. Overexpression of sox9 rescued the zebrafish chondrogenic and craniofacial phenotype generated by ddrgk1 knockdown, thus identifying DDRGK1 as a regulator of SOX9. Consistent with these results, Ddrgk1-/- mice displayed delayed limb bud chondrogenic condensation, decreased SOX9 protein expression and Col2a1 transcript levels, and increased apoptosis. Furthermore, we determined that DDRGK1 can directly bind to SOX9 to inhibit its ubiquitination and proteasomal degradation. Taken together, these data indicate that loss of DDRGK1 decreases SOX9 expression and causes a human skeletal dysplasia, identifying a mechanism that regulates chondrogenesis via modulation of SOX9 ubiquitination.

Altered mRNA Splicing, Chondrocyte Gene Expression and Abnormal Skeletal Development due to SF3B4 Mutations in Rodriguez Acrofacial Dysostosis

The acrofacial dysostoses (AFD) are a genetically heterogeneous group of inherited disorders with craniofacial and limb abnormalities. Rodriguez syndrome is a severe, usually perinatal lethal AFD, characterized by severe retrognathia, oligodactyly and lower limb abnormalities. Rodriguez syndrome has been proposed to be a severe form of Nager syndrome, a non-lethal AFD that results from mutations in SF3B4, a component of the U2 small nuclear ribonucleoprotein particle (U2 snRNP). Furthermore, a case with a phenotype intermediate between Rodriguez and Nager syndromes has been shown to have an SF3B4 mutation. We identified heterozygosity for SF3B4 mutations in Rodriguez syndrome, confirming that the phenotype is a dominant disorder that is allelic with Nager syndrome. The mutations led to reduced SF3B4 synthesis and defects in mRNA splicing, primarily exon skipping. The mutations also led to reduced expression in growth plate chondrocytes of target genes, including the DLX5, DLX6, SOX9, and SOX6 transcription factor genes, which are known to be important for skeletal development. These data provide mechanistic insight toward understanding how SF3B4 mutations lead to the skeletal abnormalities observed in the acrofacial dysostoses.

The acrofacial dysostoses (AFD) are inherited disorders with abnormalities of the facial and limb bones. Rodriguez syndrome is a severe type of AFD that is usually lethal in the immediate perinatal period. Rodriguez syndrome has been proposed to be a severe form of Nager syndrome, a non-lethal AFD that results from mutations in SF3B4, a component of mRNA splicing machinery needed for proper maturation of primary transcripts. Furthermore, a case with a phenotype intermediate between Rodriguez and Nager syndromes has been shown to have an SF3B4 mutation. We found that mutations in SF3B4 produce Rodriguez syndrome, further demonstrating that it is allelic with Nager syndrome. The consequences of the mutations include abnormal splicing and reduced expression in growth plate chondrocytes of genes that are important for proper development of the skeleton, providing mechanistic insight toward understanding how SF3B4 mutations lead to the skeletal abnormalities observed in the acrofacial dysostoses.

IFT52 mutations destabilize anterograde complex assembly, disrupt ciliogenesis and result in short rib polydactyly syndrome

The short-rib polydactyly syndromes (SRPS) encompass a radiographically and genetically heterogeneous group of skeletal ciliopathies that are characterized by a long narrow chest, short extremities, and variable occurrence of polydactyly. Radiographic abnormalities include undermineralization of the calvarium, shortened and bowed appendicular bones, trident shaped acetabula and polydactyly. In a case of SRPS we identified compound heterozygosity for mutations in IFT52, which encodes a component of the anterograde intraflagellar transport complex. The IFT52 mutant cells synthesized a significantly reduced amount of IFT52 protein, leading to reduced synthesis of IFT74, IFT81, IFT88 and ARL13B, other key anterograde complex members. Ciliogenesis was also disrupted in the mutant cells, with a 60% reduction in the presence of cilia on mutant cells and loss of cilia length regulation for the cells with cilia. These data demonstrate that IFT52 is essential for anterograde complex integrity and for the biosynthesis and maintenance of cilia. The data identify a new locus for SRPS and show that IFT52 mutations result in a ciliopathy with primary effects on the skeleton.

Patient navigation to increase colorectal cancer screening among Latino Medicare enrollees: a randomized controlled trial

PURPOSE

Latino Medicare enrollees report suboptimal rates of colorectal cancer screening (CRCS) despite Medicare policies designed to improve CRCS access for older persons. Patient navigation (PN) may address many underlying barriers to CRCS, yet little is known about the effectiveness of PN to increase CRCS adherence among Latino Medicare enrollees.

METHODS

Using a randomized controlled trial study design, we evaluated tailored PN delivered outside of primary care settings as an intervention to increase CRCS adherence in this population. Intervention participants (n = 135) received tailored PN services which included education, counseling, and logistical support administered in their language of choice. Comparison participants (n = 168) received mailed cancer education materials. We compared CRCS rates between interventions and used multivariable logistic regression to assess the odds of CRCS adherence for PN versus comparison groups after adjusting for covariates of interest.

RESULTS

More navigated than non-navigated participants became CRCS adherent during the study period (43.7 vs. 32.1%, p = 0.04). The odds of CRCS adherence were significantly higher for PN relative to comparison participants before and after adjusting for covariates (unadjusted OR 1.64, p = 0.04; adjusted OR 1.82, p = 0.02). Higher CRCS adherence rates were observed primarily in the uptake of endoscopic screening methods.

CONCLUSION

This study demonstrates that PN delivered outside of the primary care environment is modestly effective in increasing CRCS adherence among Latino Medicare enrollees. This intervention strategy should be further evaluated as a complement to primary care-based PN and other care coordination strategies to increase adherence with CRCS and other evidence-based screenings among older Latinos.

HSP47 and FKBP65 cooperate in the synthesis of type I procollagen

Osteogenesis imperfecta (OI) is a genetic disorder that results in low bone mineral density and brittle bones. Most cases result from dominant mutations in the type I procollagen genes, but mutations in a growing number of genes have been identified that produce autosomal recessive forms of the disease. Among these include mutations in the genes SERPINH1 and FKBP10, which encode the type I procollagen chaperones HSP47 and FKBP65, respectively, and predominantly produce a moderately severe form of OI. Little is known about the biochemical consequences of the mutations and how they produce OI. We have identified a new OI mutation in SERPINH1 that results in destabilization and mislocalization of HSP47 and secondarily has similar effects on FKBP65. We found evidence that HSP47 and FKBP65 act cooperatively during posttranslational maturation of type I procollagen and that FKBP65 and HSP47 but fail to properly interact in mutant HSP47 cells. These results thus reveal a common cellular pathway in cases of OI caused by HSP47 and FKBP65 deficiency.

WNT1 mutations in early-onset osteoporosis and osteogenesis imperfecta

This report identifies human skeletal diseases associated with mutations in WNT1. In 10 family members with dominantly inherited, early-onset osteoporosis, we identified a heterozygous missense mutation in WNT1, c.652T→G (p.Cys218Gly). In a separate family with 2 siblings affected by recessive osteogenesis imperfecta, we identified a homozygous nonsense mutation, c.884C→A, p.Ser295*. In vitro, aberrant forms of the WNT1 protein showed impaired capacity to induce canonical WNT signaling, their target genes, and mineralization. In mice, Wnt1 was clearly expressed in bone marrow, especially in B-cell lineage and hematopoietic progenitors; lineage tracing identified the expression of the gene in a subset of osteocytes, suggesting the presence of altered cross-talk in WNT signaling between the hematopoietic and osteoblastic lineage cells in these diseases.

Dominant and recessive forms of fibrochondrogenesis resulting from mutations at a second locus, COL11A2

Fibrochondrogenesis is a severe, recessively inherited skeletal dysplasia shown to result from mutations in the gene encoding the proα1(XI) chain of type XI collagen, COL11A1. The first of two cases reported here was the affected offspring of first cousins and sequence analysis excluded mutations in COL11A1. Consequently, whole-genome SNP genotyping was performed to identify blocks of homozygosity, identical-by-descent, wherein the disease locus would reside. COL11A1 was not within a region of homozygosity, further excluding it as the disease locus, but the gene encoding the proα2(XI) chain of type XI collagen, COL11A2, was located within a large region of homozygosity. Sequence analysis identified homozygosity for a splice donor mutation in intron 18. Exon trapping demonstrated that the mutation resulted in skipping of exon 18 and predicted deletion of 18 amino acids from the triple helical domain of the protein. In the second case, heterozygosity for a de novo 9 bp deletion in exon 40 of COL11A2 was identified, indicating that there are autosomal dominant forms of fibrochondrogenesis. These findings thus demonstrate that fibrochondrogenesis can result from either recessively or dominantly inherited mutations in COL11A2.

Fibrochondrogenesis results from mutations in the COL11A1 type XI collagen gene

Fibrochondrogenesis is a severe, autosomal-recessive, short-limbed skeletal dysplasia. In a single case of fibrochondrogenesis, whole-genome SNP genotyping identified unknown ancestral consanguinity by detecting three autozygous regions. Because of the predominantly skeletal nature of the phenotype, the 389 genes localized to the autozygous intervals were prioritized for mutation analysis by correlation of their expression with known cartilage-selective genes via the UCLA Gene Expression Tool, UGET. The gene encoding the α1 chain of type XI collagen (COL11A1) was the only cartilage-selective gene among the three candidate intervals. Sequence analysis of COL11A1 in two genetically independent fibrochondrogenesis cases demonstrated that each was a compound heterozygote for a loss-of-function mutation on one allele and a mutation predicting substitution for a conserved triple-helical glycine residue on the other. The parents who were carriers of missense mutations had myopia. Early-onset hearing loss was noted in both parents who carried a loss-of-function allele, suggesting COL11A1 as a locus for mild, dominantly inherited hearing loss. These findings identify COL11A1 as a locus for fibrochondrogenesis and indicate that there might be phenotypic manifestations among carriers.

BMPER mutation in diaphanospondylodysostosis identified by ancestral autozygosity mapping and targeted high-throughput sequencing

Diaphanospondylodysostosis (DSD) is a rare, recessively inherited, perinatal lethal skeletal disorder. The low frequency and perinatal lethality of DSD makes assembling a large set of families for traditional linkage-based genetic approaches challenging. By searching for evidence of unknown ancestral consanguinity, we identified two autozygous intervals, comprising 34 Mbps, unique to a single case of DSD. Empirically testing for ancestral consanguinity was effective in localizing the causative variant, thereby reducing the genomic space within which the mutation resides. High-throughput sequence analysis of exons captured from these intervals demonstrated that the affected individual was homozygous for a null mutation in BMPER, which encodes the bone morphogenetic protein-binding endothelial cell precursor-derived regulator. Mutations in BMPER were subsequently found in three additional DSD cases, confirming that defects in BMPER produce DSD. Phenotypic similarities between DSD and Bmper null mice indicate that BMPER-mediated signaling plays an essential role in vertebral segmentation early in human development.

TREM-2 (triggering receptor expressed on myeloid cells 2) is a phagocytic receptor for bacteria

Phagocytosis, which is essential for the immune response to pathogens, is initiated by specific interactions between pathogens and cell surface receptors expressed by phagocytes. This study identifies triggering receptor expressed on myeloid cells 2 (TREM-2) and its signaling counterpart DAP12 as a molecular complex that promotes phagocytosis of bacteria. Expression of TREM-2–DAP12 enables nonphagocytic Chinese hamster ovary cells to internalize bacteria. This function depends on actin cytoskeleton dynamics and the activity of the small guanosine triphosphatases Rac and Cdc42. Internalization also requires src kinase activity and tyrosine phosphorylation. In bone marrow–derived macrophages, phagocytosis is decreased in the absence of DAP12 and can be restored by expression of TREM-2–DAP12. Depletion of TREM-2 inhibits both binding and uptake of bacteria. Finally, TREM-2–dependent phagocytosis is impaired in Syk-deficient macrophages. This study highlights a novel role for TREM-2–DAP12 in the immune response to bacterial pathogens.

[Does blastic crisis as revealed in chronic myeloid leukemia simulate either acute primary leukemia or acute primary leukemia with Philadelphia chromosome?]

In ten cases of apparently primary acute leukaemia, the discovery of a Philadelphia chromosome at routine examination of the caryotype led a diagnosis of blastic crisis of chronic myeloid leukemia. The clinical, cytological and cytogenetic pictures varied and only routine caryotypic examination may be used in reaching the diagnosis. The prognosis appear to be less bad than in blastic crises occurring after a long course of chronic myeloid leukaemia and closer to that of primary acute myeloid leukaemia.