Treatment of joint disease that results in limited flexion is often rejected by patients in non-Western cultures whose activities of daily living require a higher range of motion at the hip, knee, or ankle. However, limited information is available about the joint kinematics required for high range of motion activities, such as squatting, kneeling, and sitting cross-legged, making it difficult to design prosthetic implants that will meet the needs of these populations. Therefore, the objective of this work was to generate three-dimensional kinematics at the hip, knee, and ankle joints of Indian subjects while performing activities of daily living. Thirty healthy Indian subjects (average age: 48.2 AE 7.6 years) were asked to perform six trials of the following activities: squatting, kneeling, and sitting cross-legged. Floating axis angles were calculated at the joints using the kinematic data collected by an electromagnetic motion tracking device with receivers located on the subject's foot, shank, thigh, and sacrum. A mean maximum flexion of 1578 AE 68 at the knee joint was required for squatting with heels up. Mean maximum hip flexion angles reached up to 958 AE 278 for squatting with heels flat. The high standard deviation associated with this activity underscored the large range in maximum hip flexion angles required by different subjects. Mean ankle range of flexion reached 588 AE 148 for the sitting cross-legged activity. The ranges of motion required to perform the activities studied are greater than that provided by most currently available joint prostheses, demonstrating the need for high range of motion implant design. ß

Complex I (NADH:ubiquinone oxidoreductase) is the first and largest multimeric complex of the mitochondrial respiratory chain. Human complex I comprises seven subunits encoded by mitochondrial DNA and 38 nuclear-encoded subunits that are assembled together in a process that is only partially understood. To date, mutations causing complex I deficiency have been described in all 14 core subunits, five supernumerary subunits, and four assembly factors. We describe complex I deficiency caused by mutation of the putative complex I assembly factor C20orf7. A candidate region for a lethal neonatal form of complex I deficiency was identified by homozygosity mapping of an Egyptian family with one affected child and two affected pregnancies predicted by enzyme-based prenatal diagnosis. The region was confirmed by microcell-mediated chromosome transfer, and 11 candidate genes encoding potential mitochondrial proteins were sequenced. A homozygous missense mutation in C20orf7 segregated with disease in the family. We show that C20orf7 is peripherally associated with the matrix face of the mitochondrial inner membrane and that silencing its expression with RNAi decreases complex I activity. C20orf7 patient fibroblasts showed an almost complete absence of complex I holoenzyme and were defective at an early stage of complex I assembly, but in a manner distinct from the assembly defects caused by mutations in the assembly factor NDUFAF1. Our results indicate that C20orf7 is crucial in the assembly of complex I and that mutations in C20orf7 cause mitochondrial disease.

Complex IV is the terminal enzyme of the mitochondrial respiratory chain. In humans, biogenesis of complex IV involves the coordinated assembly of 13 subunits encoded by both mitochondrial and nuclear genomes. The early stages of complex IV assembly involving mitochondrial DNA‐encoded subunits CO1 and CO2 have been well studied. However, the latter stages, during which many of the nuclear DNA‐encoded subunits are incorporated, are less well understood. Using in vitro import and assembly assays, we found that subunits Cox6a, Cox6b and Cox7a assembled into pre‐existing complex IV, while Cox4‐1 and Cox6c subunits assembled into subcomplexes that may represent rate‐limiting intermediates. We also found that Cox6a and Cox7a are incorporated into a novel intermediate complex of approximately 250 kDa, and that transition of subunits from this complex to the mature holoenzyme had stalled in the mitochondria of patients with isolated complex IV deficiency. A number of complex IV subunits were also found to integrate into supercomplexes containing combinations of complex I, dimeric complex III and complex IV. Subunit assembly into these supercomplexes was also observed in mitochondria of patients in whom monomeric complex IV was selectively reduced. We conclude that newly imported nuclear DNA‐encoded subunits can integrate into the complex IV holoenzyme and supercomplex forms by associating with pre‐existing subunits and intermediate assembly complexes.