Andrew M. Ho

Mutations in ANKH Cause Chondrocalcinosis

Chondrocalcinosis (CC) is a common cause of joint pain and arthritis that is caused by the deposition of calcium-containing crystals within articular cartilage. Although most cases are sporadic, rare familial forms have been linked to human chromosomes 8 (CCAL1) or 5p (CCAL2) (Baldwin et al. 1995; Hughes et al. 1995; Andrew et al. 1999). Here, we show that two previously described families with CCAL2 have mutations in the human homolog of the mouse progressive ankylosis gene (ANKH). One of the human mutations results in the substitution of a highly conserved amino acid residue within a predicted transmembrane segment. The other creates a new ATG start site that adds four additional residues to the ANKH protein. Both mutations segregate completely with disease status and are not found in control subjects. In addition, 1 of 95 U.K. patients with sporadic CC showed a deletion of a single codon in the ANKH gene. The same change was found in a sister who had bilateral knee replacement for osteoarthritis. Each of the three human mutations was reconstructed in a full-length ANK expression construct previously shown to regulate pyrophosphate levels in cultured cells in vitro. All three of the human mutations showed significantly more activity than a previously described nonsense mutation that causes severe hydroxyapatite mineral deposition and widespread joint ankylosis in mice. These results suggest that small sequence changes in ANKH are one cause of CC and joint disease in humans. Increased ANK activity may explain the different types of crystals commonly deposited in human CCAL2 families and mutant mice and may provide a useful pharmacological target for treating some forms of human CC.

Bone Regeneration Mediated by BMP4-Expressing Muscle-Derived Stem Cells Is Affected by Delivery System

This study investigated the delivery of bone morphogenetic protein (BMP)4-secreting muscle-derived stem cells (MDSC-B4) capable of inducing bone formation in mice using collagen gel (CG), fibrin sealant (FS), and gelatin sponge carriers. After implanting these various cell-loaded scaffolds intramuscularly or into critical-size skull defects, we measured the extent of heterotopic ossification and calvarial defect healing over a 6-week period via radiographic, radiomorphometric, histological, and micro-computed tomography analyses. As expected, in the absence of MDSC-B4, there was no ectopic ossification and only minimal calvarial regeneration using each type of scaffold. Although CG and gelatin sponges loaded with BMP4-secreting cells produced the most ectopic bone, FS constructs produced bone with comparably less mineralization. In the mouse calvaria, we observed MDSC-B4-loaded scaffolds able to promote bone defect healing to a variable degree, but there were differences between these implants in the volume, shape, and morphology of regenerated bone. MDSC-B4 delivery in a gelatin sponge produced hypertrophic bone, whereas delivery in a CG and FS healed the defect with bone that closely resembled the quantity and configuration of native calvarium. In summary, hydrogels are suitable carriers for osteocompetent MDSCs in promoting bone regeneration, especially at craniofacial injury sites.

Radial Artery Perforator Flap

Soft tissue defects in the hand and wrist can be challenging problems for the hand surgeon. The retrograde radial forearm fasciocutaneous flap has emerged in recent years as the workhorse flap to cover many hand and wrist defects. However, recognition of the intrinsic limitations of this flap has led to the development of other alternative flaps to provide soft tissue coverage for this region. The radial artery perforator flap has many of the benefits of the radial forearm flap but minimizes the disadvantages, such as the need to sacrifice the radial artery, color and bulk mismatch of the flap and recipient tissues, and donor site appearance. In this article, we will review the indications for using the radial artery perforator flap to cover hand and wrist soft tissue defects. We will discuss the surgical anatomy, indications, operating technique, rehabilitation protocol, potential complications, and pearls and pitfalls for use of this flap for upper-extremity defects.

Dominant negative Bmp5 mutation reveals key role of BMPs in skeletal response to mechanical stimulation

BackgroundOver a hundred years ago, Wolff originally observed that bone growth and remodeling are exquisitely sensitive to mechanical forces acting on the skeleton. Clinical studies have noted that the size and the strength of bone increase with weight bearing and muscular activity and decrease with bed rest and disuse. Although the processes of mechanotransduction and functional response of bone to mechanical strain have been extensively studied, the molecular signaling mechanisms that mediate the response of bone cells to mechanical stimulation remain unclear.ResultsHere, we identify a novel germline mutation at the mouse Bone morphogenetic protein 5 (Bmp5) locus. Genetic analysis shows that the mutation occurs at a site encoding the proteolytic processing sequence of the BMP5 protein and blocks proper processing of BMP5. Anatomic studies reveal that this mutation affects the formation of multiple skeletal features including several muscle-induced skeletal sites in vivo. Biomechanical studies of osteoblasts from these anatomic sites show that the mutation inhibits the proper response of bone cells to mechanical stimulation.ConclusionThe results from these genetic, biochemical, and biomechanical studies suggest that BMPs are required not only for skeletal patterning during embryonic development, but also for bone response and remodeling to mechanical stimulation at specific anatomic sites in the skeleton.

Isolated Complete Heart Block in the Fetus

Isolated congenital complete heart block (CCHB) is a rare disease with significant associated morbidity and mortality. A diagnosis is often made in fetal life, but data regarding long-term outcomes are limited, and fetal therapy to improve prognosis is controversial. In our institution, 85 fetuses were diagnosed with CCHB from 1981 to 2013 in 80 mothers. There were 37 anti-Ro-positive pregnancies, 36 both anti-Ro and anti-La positive, 10 antibody negative, and 2 of unknown antibody status. Antenatal treatments were given in 14 fetuses, with 8 given fluorinated steroids, 4 beta sympathomimetics, and both in 2. Of the original 85, 74 babies survived to delivery. Fetal hydrops was the only risk factor found to be significantly associated with intrauterine death (p <0.001). Four babies died before pacemaker implantation, 56 have had pacemakers implanted, and 14 are pacemaker free. The Kaplan-Meier estimate for median time to pacemaker implantation was 2.6 years, with 15 implanted in the neonatal period. There have been 14 postnatal deaths, with a Kaplan-Meier estimate of survival at 30 years of 76.8% (95% confidence interval 65% to 90%). Dilated cardiomyopathy was uncommon, occurring in 6 patients. Prematurity and hydrops were associated with increased postnatal mortality (p = 0.02 and 0.005, respectively). In conclusion, we present the largest single-unit experience of prenatally diagnosed CCHB in the published literature. Our cohort was conservatively managed, with survival similar to those previously published. These data offer insight into the long-term natural history of CCHB.