Mineralization is a biological process that consists in the deposition of calcium phosphate in the extracellular matrix of bones and all calcified tissues. In addition to the fundamental function of support, the skeletal mineral constitutes the organism’s main calcium reserve, useful for compensating any imbalances of this vital element.
There are many pathologies linked to defects in the mineralization process:
- When mineralization is reduced or absent, there is a condition of “soft bone”, called osteomalacia in adults and rickets in children. In this case, the fragile bone will be susceptible to deformations, fractures and pain.
- When mineralization is excessive it is called bone sclerosis, which rather than giving strength and hardness to the bone, induces a reduction in normal remodeling and damage repair, resulting in structural fragility and increased susceptibility to fractures.
This type of disorders constitute a heterogeneous group of rare inherited diseases caused by gene mutations on one or more of the many genes involved in the regulation of calcium homeostasis.
Among the main inherited disorders of the mineralization we find:
- Hypophosphatasia: it is caused by a defect on the ALPL gene, which encodes the enzyme alkaline phosphatase (TNS-ALP) not tissue-specific, which leads to a reduction in bone mineralization. The clinical spectrum of the disease is extremely variable. The most severe forms present severe rickets, bone fragility, multiple fractures, osteoarticular pain and even neurological affections (convulsions, seizures, encephalopathy, insomnia, anxiety, and depression).
- Osteogenesis imperfecta: includes a heterogeneous group of genetic diseases characterized by a decrease in mineralized bone mass, which results in increased skeletal fragility, and a susceptibility to multiple bone fractures of varying severity.
- Disorders of phosphate metabolism: it is caused by mutations in the genes that code for proteins that lead to a reduction of phosphate, the ion that with calcium builds up the bone crystal, hydroxyphosphite, in those diseases we find generalized reduced bone mineralization (rickets), bone deformities, fragility fractures, short stature, tooth loss. In addition, there are also mutations on the genes that induce an increase in phosphate in the blood and that are responsible for congenital hyperphosphatemic tumor calcinosis which occurs with the deposition of calcium phosphate crystals in the skin, muscles, tendons and ligaments.