Homocysteinemia due to MTHFR deficiency in a young adult presenting with bilateral lens subluxations.

The most common cause of isolated inherited homocysteinemia is a deficiency of the enzyme cystathionine ß-synthase (CBS). Clinical manifestations of CBS deficiency can include ectopia lentis, thromboembolism, marfanoid habits, and intellectual disability. CBS deficiency, which affects the transsulfuration pathway, is marked biochemically by elevated serum homocysteine and plasma methionine. We report a patient with homocysteinemia, low plasma methionine, and no significant neurological abnormalities who presented with bilateral subluxated crystalline lenses due to a 5,10-methylenetetrahydrofolate reductase (MTHFR) deficiency. MTHFR deficiency, a disorder in the remethylation pathway, can cause mild to severe disease, although most presentations include neurological involvement. MTHFR deficiency has not been previously associated with lens subluxation or complete dislocation. Prolonged exposure to elevated serum homocysteine levels is most likely the explanation for her ectopia lentis. This case expands the differential diagnosis of homocysteinemia and highlights the need for a correct diagnosis to optimize the clinical outcome of patients with this condition.

Observations of ejecta clouds produced by impacts onto Saturn's rings.

We report observations of dusty clouds in Saturn's rings, which we interpret as resulting from impacts onto the rings that occurred between 1 and 50 hours before the clouds were observed. The largest of these clouds was observed twice; its brightness and cant angle evolved in a manner consistent with this hypothesis. Several arguments suggest that these clouds cannot be due to the primary impact of one solid meteoroid onto the rings, but rather are due to the impact of a compact stream of Saturn-orbiting material derived from previous breakup of a meteoroid. The responsible interplanetary meteoroids were initially between 1 centimeter and several meters in size, and their influx rate is consistent with the sparse prior knowledge of smaller meteoroids in the outer solar system.

Risk assessment in human immunodeficiency virus-associated acute myeloid leukemia.

CD4 count ≤200×10(6) cells/L has been identified as a predictor of short survival in HIV-associated acute myeloid leukemia (HIV-AML), but karyotype, which is the best predictor of survival in AML, has not been evaluated in HIV-AML patients. A retrospective cohort of 31 patients was created from 9 local cases and 22 published cases. HIV-AML karyotypes were heterogeneous and were similar in distribution to those in HIV-negative AML. Among intensively treated patients, most achieved complete remission, but succumbed to infectious complications, mostly non-opportunistic, during consolidation therapy. Median survival for intensively-treated patients with CD4 counts ≤200×10(6) cells/L was 8.5 months, compared to 48 months for those with >200×10(6) CD4 cells/L (p=0.03). In contrast, AML karyotype did not predict survival (p=0.43), albeit with small numbers in each karyotype group. Thus, CD4 count is a strong predictor of short survival in HIV-AML patients regardless of karyotype. Studies evaluating innovative strategies for infection prophylaxis and for improving immune reconstitution are needed.

Rituximab treatment for thrombotic thrombocytopenic purpura associated with human immunodeficiency virus failing extensive treatment with plasma exchange: a report of two cases.

In an urban area with a 3% prevalence of HIV infection, two women presented in a 1-year period with AIDS and thrombotic thrombocytopenic purpura (TTP). TTP was diagnosed in each patient based on the presence of thrombocytopenia, schistocytes, and markedly elevated lactate dehydrogenase (LDH) activity. Initial treatment with plasma exchange resulted in resolution of these abnormalities. However, the discontinuation of plasma exchange resulted in the prompt recurrence of laboratory abnormalities diagnostic for TTP. Treatment failure was established after observing 6 and 4 such responses requiring 41 and 40 episodes of plasma exchange for each patient, respectively. Patients were subsequently treated with 2-4 doses of weekly rituximab resulting in durable remission. These patients are now 21 and 9 months beyond rituximab treatment. Rituximab appears to be safe and effective in this setting.

The determination of the structure of Saturn's F ring by nearby moonlets.

Saturn's narrow F ring exhibits several unusual features that vary on timescales of hours to years. These include transient clumps, a central core surrounded by a multistranded structure and a regular series of longitudinal channels associated with Prometheus, one of the ring's two 'shepherding' satellites. Several smaller moonlets and clumps have been detected in the ring's immediate vicinity, and a population of embedded objects has been inferred. Here we report direct evidence of moonlets embedded in the ring's bright core, and show that most of the F ring's morphology results from the continual gravitational and collisional effects of small satellites, often combined with the perturbing effect of Prometheus. The F-ring region is perhaps the only location in the Solar System where large-scale collisional processes are occurring on an almost daily basis.

How Prometheus creates structure in Saturn's F ring.

Images of Saturn's narrow and contorted F ring returned by the Cassini spacecraft have revealed phenomena not previously detected in any planetary ring system. The perturbing effect of the inner shepherding satellite, Prometheus, seems to introduce channels through the F ring and a 'streamer'--a line of particles that link the ring to the satellite. The detailed mechanism for the formation of these features has been lacking an explanation. Here we show that these phenomena can be understood in terms of a simple gravitational interaction as Prometheus approaches and recedes from the F ring every 14.7 hours. Our numerical models show that as Prometheus recedes from its closest approach to the F ring, it draws out ring material; one orbital period later, this affected region has undergone keplerian shear and is visible as a channel, in excellent agreement with structures seen in the Cassini images. Prometheus' periodic disruption of the F ring will become more pronounced as the two orbits approach their minimum separation in 2009. The model predicts that the appearance of streamers and the associated channels will vary in a regular fashion on a timescale of one orbital period.

Imaging of Titan from the Cassini spacecraft.

Titan, the largest moon of Saturn, is the only satellite in the Solar System with a substantial atmosphere. The atmosphere is poorly understood and obscures the surface, leading to intense speculation about Titan's nature. Here we present observations of Titan from the imaging science experiment onboard the Cassini spacecraft that address some of these issues. The images reveal intricate surface albedo features that suggest aeolian, tectonic and fluvial processes; they also show a few circular features that could be impact structures. These observations imply that substantial surface modification has occurred over Titan's history. We have not directly detected liquids on the surface to date. Convective clouds are found to be common near the south pole, and the motion of mid-latitude clouds consistently indicates eastward winds, from which we infer that the troposphere is rotating faster than the surface. A detached haze at an altitude of 500 km is 150-200 km higher than that observed by Voyager, and more tenuous haze layers are also resolved.