In patients with Alzheimer's disease, amyloid fibrils that are aggregates of A4 protein subunits are deposited in the brain. A similar process occurs at an earlier age in persons with Down's syndrome. To investigate the deposition of amyloid in these diseases, we used a radioimmunoassay to measure levels of the amyloid precursor (PreA4) in the serum of 17 patients with Down's syndrome, 15 patients with Alzheimer's disease, and 33 normal elderly controls. The mean (+/- SD) concentration of serum PreA4 was increased 1.5-fold in patients with Down's syndrome (2.49 +/- 1.13 nmol per liter) as compared with that in controls (1.68 +/- 0.49 nmol per liter; P less than 0.007); the levels in patients with Alzheimer's disease were similar to those in controls (1.83 +/- 0.78; P less than 0.98). We also found that the concentration of PreA4 in the brain tissue of two adults with Down's syndrome (100 and 190 pmol per gram) was higher than that in the brain tissue of either 26 patients with Alzheimer's disease (64.4 +/- 17.3 pmol per gram) or 17 elderly controls with neurologic disease (68.5 +/- 26.3 pmol per gram). Immunocytochemical studies of brain tissue from 26 patients with Down's syndrome showed that the deposition of A4 protein amyloid began in these patients approximately 50 years earlier than it began in 127 normal aging subjects studied previously, although the rate of deposition was the same. We conclude that, since the gene for PreA4 is on the long arm of chromosome 21, which is present in triplicate in Down's syndrome, overexpression of this gene may lead to increased levels of PreA4 and amyloid deposition in Down's syndrome. However, since increased levels of PreA4 are not present in Alzheimer's disease, additional factors must account for the amyloid deposition in that disorder.

The calcium (Ca) metabolism of established human lactation was studied in 40 adult women (mean age 32.4 years) who had been breast-feeding for 6 months (Lac) and in 40 age-matched controls (Con) using fasting urine and blood biochemistry and forearm single-photon bone mineral densitometry (BMD). Serial studies were performed up to 6 months after weaning in Lac women and repeated once in Con women. During lactation the significant findings were (1) a selective reduction (7.1%, P less than 0.03) in BMD at the ultradistal site containing 60% trabecular bone, but not at two more proximal, chiefly cortical bone sites; (2) increased bone turnover affecting bone resorption [fasting hydroxyproline excretion, Lac 2.22 +/- 0.12 mumol/liter GF (mean +/- SEM), Con 1.19 +/- 0.04, P less than 0.001] and affecting bone formation (plasma alkaline phosphatase, Lac 81.9 +/- 2.5 IU/liter, Con 53.5 +/- 2.7, P less than 0.001, and serum osteocalcin, Lac 14.0 +/- 0.7 microgram/liter, Con 7.3 +/- 0.4, P less than 0.001); and (3) renal conservation in the fasting state of both Ca and inorganic phosphate (Pi) with a resultant moderate increase in plasma Pi but not in plasma Ca (total or ionized). There were no differences between the groups in serum parathyroid hormone (PTH, intact and midmolecule assays), 25-hydroxy- and 1,25-dihydroxyvitamin D, nephrogenous cyclic AMP production, or plasma creatinine.(ABSTRACT TRUNCATED AT 250 WORDS)

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The changes in three different indices of 1,25-dihydroxyvitamin D (1,25(OH)2D) biological activity were studied longitudinally in 35 women during late pregnancy and lactation and in 26 control women. Measurements were made of maternal serum total 1,25(OH)2D and free 1,25(OH)2D concentration (by centrifugal ultrafiltration) and the free 1,25(OH)2D index (the molar ratio of total 1,25(OH)2D and vitamin D binding protein (DBP]. During late pregnancy total 1,25(OH)2D concentrations were significantly elevated when compared to controls, as were free 1,25(OH)2D and DBP concentrations and the free 1,25(OH)2D index. Serum total 1,25(OH)2D, free 1,25(OH)2D and DBP concentrations all fell dramatically during the first 2 weeks of lactation with total 1,25(OH)2D and free 1,25(OH)2D concentrations falling to levels below those of controls. During the course of lactation both total 1,25(OH)2D and free 1,25(OH)2D levels rose significantly although they were not different from controls at 18 weeks of lactation. In contrast, the free 1,25(OH)2D index fell during the first 2 weeks of lactation, but remained at this level, significantly lower than controls. Neither urinary calcium excretion nor dietary calcium intake correlated with total or free 1,25(OH)2D, DBP, or the free 1,25(OH)2D index. The disagreement in the results of free 1,25(OH)2D concentration and free 1,25(OH)2D index demonstrates that these two approaches to measuring biologically active 1,25(OH)2D are not equivalent. In attempting to account for the increased calcium requirements of human reproduction we conclude that in pregnancy any of the 1,25(OH)2D measurements may be appropriate. In lactation, however, either 1,25(OH)2D is not a major factor or 1,25(OH)2D biological activity is inadequately represented by any of the currently available methods.