Developmental basis for hind-limb loss in dolphins and origin of the cetacean bodyplan.

Among mammals, modern cetaceans (whales, dolphins, and porpoises) are unusual in the absence of hind limbs. However, cetacean embryos do initiate hind-limb bud development. In dolphins, the bud arrests and degenerates around the fifth gestational week. Initial limb outgrowth in amniotes is maintained by two signaling centers, the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA). Our data indicate that the cetacean hind-limb bud forms an AER and that this structure expresses Fgf8 initially, but that neither the AER nor Fgf8 expression is maintained. Moreover, Sonic hedgehog (Shh), which mediates the signaling activity of the ZPA, is absent from the dolphin hind-limb bud. We find that failure to establish a ZPA is associated with the absence of Hand2, an upstream regulator of Shh. Interpreting our results in the context of both the cetacean fossil record and the known functions of Shh suggests that reduction of Shh expression may have occurred approximately 41 million years ago and led to the loss of distal limb elements. The total loss of Shh expression may account for the further loss of hind-limb elements that occurred near the origin of the modern suborders of cetaceans approximately 34 million years ago. Integration of paleontological and developmental data suggests that hind-limb size was reduced by gradually operating microevolutionary changes. Long after locomotor function was totally lost, modulation of developmental control genes eliminated most of the hind-limb skeleton. Hence, macroevolutionary changes in gene expression did not drive the initial reduction in hind-limb size.

Linking people with AIDS in rural communities: the telephone group.

People with acquired immune deficiency syndrome (AIDS) living in rural areas have difficulty obtaining needed information and support. Bringing support groups into the homes of rural residents through telephone conference call technology is an innovative practice strategy to address this problem. The authors describe the development, implementation, and evaluation of a model program consisting of six telephone group sessions. The goals of the psychoeducational group were to increase information and social support, reduce feelings of isolation, and enhance individual coping with living with AIDS.

Surgical spectrum of aortic stenosis in children: a thirty-year experience with 257 children.

Aortic stenosis accounts for 5 to 6% of infants and children seen for surgical repair of congenital heart disease. The clinical presentation and reported results of operation for aortic stenosis are highly variable. This retrospective review was undertaken to assess our operative mortality and the degree of gradient reduction afforded by each of several surgical techniques used to treat aortic stenosis in children over a 30-year period. Two hundred fifty-seven patients ranging in age from 1 day to 19 years were operated on between 1957 and 1986. The indication for operation included asymptomatic patients with gradients greater than 50 mm Hg to patients in profound cardiogenic shock. The operative mortality for children older than 6 months was 4%, whereas neonates seen with critical aortic stenosis had a 60% mortality. The late mortality was 2%. Eighty percent of surviving patients to date have undergone cardiac catheterization after repair. This shows an overall reduction of 57 mm Hg in the left ventricular-aortic gradient. Patients with supravalvular aortic stenosis and discrete subvalvular aortic stenosis as well as patients undergoing aortic valve replacement showed a reduction in or elimination of associated aortic insufficiency, whereas patients undergoing aortic valvotomy or neonates having valvotomy had a significant increase in demonstrable aortic insufficiency. The incidence of third-degree heart block or cerebral emboli following operation for aortic stenosis was less than 1%. However, the incidence of late bacterial endocarditis following repair was nearly 5%; six of eleven cases occurred in the group with discrete subvalvular aortic stenosis. Twenty-nine (13%) of the 223 long-term survivors have undergone a subsequent procedure for relief of residual or recurrent obstruction; 12 have had insertion of an aortic valve prosthesis, 12 have had insertion of an apicoaortic conduit, and 6 have required repeat aortic valvotomy. These data demonstrate the low operative mortality and excellent hemodynamic benefit of surgical relief of single-level aortic stenosis in children older than neonates. Conduits placed for complex obstructions or operative procedures in neonates have acceptable hemodynamic benefits, but operative mortality remains high.