In humans, low peak bone mass is a significant risk factor for osteoporosis. We report that LRP5, encoding the low-density lipoprotein receptor-related protein 5, affects bone mass accrual during growth. Mutations in LRP5 cause the autosomal recessive disorder osteoporosis-pseudoglioma syndrome (OPPG). We find that OPPG carriers have reduced bone mass when compared to age- and gender-matched controls. We demonstrate LRP5 expression by osteoblasts in situ and show that LRP5 can transduce Wnt signaling in vitro via the canonical pathway. We further show that a mutant-secreted form of LRP5 can reduce bone thickness in mouse calvarial explant cultures. These data indicate that Wnt-mediated signaling via LRP5 affects bone accrual during growth and is important for the establishment of peak bone mass.

We have recently observed a large pedigree with a new rare autosomal dominant spastic paraparesis. In three subsequent generations, 13 affected individuals presented with bilateral cataracts, gastroesophageal reflux with persistent vomiting, and spastic paraparesis with amyotrophy. Bilateral cataracts occurred in all affected individuals, with the exception of one patient who presented with a chorioretinal dystrophy, whereas clinical signs of spastic paraparesis showed a variable expressivity. Using a genomewide mapping approach, we mapped the disorder to the long arm of chromosome 10 on band q23.3-q24.2, in a 12-cM chromosomal region where additional neurologic disorders have been localized. The spectrum of phenotypic manifestations in this family is reminiscent of a smaller pedigree, reported recently, confirming the possibility of a new syndrome. Finally, the anticipation of symptoms suggests that an unstable trinucleotide repeat may be responsible for the condition.

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Tuberous sclerosis is an autosomal dominant disease whose characteristic feature is the development of multiple hamartomas in a variety of organs and tissues. Two major loci have been identified so far: TSC1 on chromosome 9q34 and TSC2 on chromosome 16p13.3. Loss of heterozygosity at 16p13.3-associated markers has been recently observed in hamartomatous lesions of some tuberous sclerosis patients. Here we report the first evidence of loss of heterozygosity at the TSC1 critical region in a giant cell astrocytoma of a familial tuberous sclerosis case. Segregation analysis showed that the 9q34 haplotype lost carried the putative normal TSC1 gene. These data support the hypothesis of both a germline and somatic loss-of-function mutation for the development of tuberous sclerosis hamartomas and suggest a tumor-suppressor-like activity also for the TSC1 gene product. Finally, the possible significance of a second small region of loss of heterozygosity at 9p21, found in the same astrocytoma, is discussed.

We studied the response to UV irradiation in cells from four patients, from three apparently unrelated families, affected by trichothiodystrophy (TTD). They showed all the symptoms of this rare autosomal recessive disorder (brittle hair with reduced sulfur content, mental and physical retardation, ichthyosis, peculiar face) together with photosensitivity. We found a decreased rate of duplicative DNA synthesis in stimulated lymphocytes, reduced survival in fibroblasts, and very low levels of unscheduled DNA synthesis (UDS) in Go lymphocytes and fibroblasts after UV irradiation. Complementation studies showed that normal values of UDS are restored in heterokaryons obtained by fusion of TTD cells with normal and xeroderma pigmentosum (XP)-complementation group A-cells. In contrast the defect is not complemented by fusion with XP-complementation group D-fibroblasts.