Novel mutations affecting LRP5 splicing in patients with osteoporosis-pseudoglioma syndrome (OPPG).

Osteoporosis-pseudoglioma sydrome (OPPG) is an autosomal recessive disorder with early-onset severe osteoporosis and blindness, caused by biallelic loss-of-function mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene. Heterozygous carriers exhibit a milder bone phenotype. Only a few splice mutations in LRP5 have been published. We present clinical and genetic data for four patients with novel LRP5 mutations, three of which affect splicing. Patients were evaluated clinically and by radiography and bone densitometry. Genetic screening of LRP5 was performed on the basis of the clinical diagnosis of OPPG. Splice aberrances were confirmed by cDNA sequencing or exon trapping. The effect of one splice mutation on LRP5 protein function was studied. A novel splice-site mutation c.1584+4A>T abolished the donor splice site of exon 7 and activated a cryptic splice site, which led to an in-frame insertion of 21 amino acids (p.E528_V529ins21). Functional studies revealed severely impaired signal transduction presumably caused by defective intracellular transport of the mutated receptor. Exon trapping was used on two samples to confirm that splice-site mutations c.4112-2A>G and c.1015+1G>T caused splicing-out of exons 20 and 5, respectively. One patient carried a homozygous deletion of exon 4 causing the loss of exons 4 and 5, as demonstrated by cDNA analysis. Our results broaden the spectrum of mutations in LRP5 and provide the first functional data on splice aberrations.

Effect of increased fluid intake on stool output in normal healthy volunteers.

Constipation is a common condition affecting millions of people throughout the world. The present study aimed to determine the effect of extra fluid intake, as recommended by many primary care physicians and gastroenterologists, on the actual stool output in normal healthy volunteers. We recruited 15 healthy volunteers (aged 23-46 years, mean 30.1) without any significant history of diarrhea or constipation to participate in our study. Nine subjects underwent extra intake of isotonic fluids (Gatorade), whereas the remainder received extra free water over their baseline. During period I (3 days), baseline diet and fluid intake were determined by a registered dietitian. During periods II and III (2 days each), the volunteers in each group increased their fluid intake by 1 and 2 l of isotonic (Gatorade) and hypotonic solution (water), respectively. Period IV (2 days) completed the study with the volunteers returning to their baseline fluid intake. Urine and stool outputs were measured in these volunteers. Additional increase in fluid intake (isotonic or free water) did not result in a significant change in stool output. However, there was a significant increase in urine output (P < 0.05). Despite common medical advice to consume extra fluid for constipation, our results indicate that extra fluid intake in normal healthy volunteers did not produce a significant increase in stool output.