Osteoporosis-Pseudoglioma Syndrome

Alternative Names

  • OPPG
  • OPS
  • Osteogenesis Imperfecta, Ocular Form
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WHO-ICD-10 version:2010

Congenital malformations, deformations and chromosomal abnormalities

Congenital malformations and deformations of the musculoskeletal system

OMIM Number

259770

Mode of Inheritance

Autosomal Recessive

Gene Map Locus

11q13.4

Description

The osteoporosis-pseudoglioma syndrome (OPPG) is a rare autosomal recessive disorder characterized by severe juvenile-onset osteoporosis, which ranges between mild to moderate, and congenital or early-onset blindness occurring due to hyperplasia of the vitreous, to corneal capacity, and to secondary glaucoma. Other manifestations include muscular hypotonia, ligamentous laxity, mild mental retardation and seizures. Prevalence of OPPG is estimated at 1 per 2,000,000 and the age of onset mainly occurs during childhood.

Molecular Genetics

Osteoporosis-pseudoglioma syndrome (OPPG) occurs due to the low density of lipoprotein receptor-related protein-5 (LRP5) which is found in the outer membrane of various cells. LRP5 consists of 1615 amino acids and has a molecular weight of 179.145 kDa.

The LRP5 gene, located on chromosome 11q11-12, is recognized as a co-receptor since it functions with another receptor protein called frizzled-4 (produced from FZD4 gene). These two genes are responsible for transmitting chemical signals from outside the cell to the cell's nucleus. Frizzled-4 and LRP5 protein are involved in Wnt signaling pathway which is a series of steps that engage in the way cells and tissues mature. The LRP5 protein plays a vital role in the development and maintenance of numerous tissues by regulating bone mineral density, directing the specialization of cells in the retina, and determining a blood supply to the retina and inner ear.

Epidemiology in the Arab World

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Other Reports

Kuwait

Teebi et al. (1988) described a sibship of two brothers and one sister from Oman suffering from osteoporosis-pseudoglioma syndrome associated with congenital heart disease. The subjects were born to phenotypically normal first cousins aged 30 years with two more healthy normal children. The three patients demonstrated visual impairment and psychomotor retardation during infancy, as well as severe platyspondyly, bilateral cataracts, joint laxity, borderline mental retardation, ventricular septal defect, and muscular hypotonia. Teebi et al. (1988) suggested an autosomal recessive inheritance for osteoporosis-pseudoglioma syndrome due to parental consanguinity and the fact that the three sibs from both sexes were affected. Furthermore, a broad range of interfamilial variability was demonstrated through studying previous and present papers proposing the existence of multiple allelism or genetic heterogeneity for this disorder.

Oman

[See: Kuwait > Teebi et al., 1988].

Tunisia

Lev et al. (2003) reported the case of two male siblings with the OPPG syndrome who were born to healthy and consanguineous parents (the father is the mother's uncle) of Tunisian Jewish ancestry. Age of the first sibling was 21 years. At age 4 months, the parents first noticed that he did not visually track. Gradual deterioration of vision and complete blindness became evident by age 6 years. At age 4 years, he had febrile convulsions followed by recurrent non-febrile complex partial seizures. At age 17 he was reexamined because of an episode of generalized seizures. Examination at age 20 showed normal growth parameters with no dysmorphic features or skin lesions, no neurologic abnormalities, and normal cognitive functions. However, he had a pigeon-chest deformity and kyphosis. A bone density study revealed severe osteoporosis. An ophthalmologic examination showed bilateral microphthalmia, nystagmus, complete opacification of the cornea and total blindness. Age of the second sibling was 15 years. At age 3 months, the parents noticed the absence of eye-tracking. Later, he was diagnosed as blind at the age of 8 months. When he was 4 years old, he had a single non-febrile generalized seizure. Findings of the eye examination were similar to those of his brother. Bone mineral density studies were performed in the two affected brothers, in the parents, in one healthy sister, and in two siblings with neurologic disability. Bone mineral density was determined in the lumbar spine (antero-posterior), femoral neck, two-thirds distal forearm (> 95% cortical bone) and ultradistal forearm (predominantly trabecular bone) by dual-energy X-ray absorptiometry.

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