A number of metabolic and genetic disorders affect bone, and some of the more important examples are listed in Table 1.

Table1. Some Metabolic & Genetic Diseases Affecting Bone & Cartilage

Osteogenesis imperfecta (brittle bones) is characterized by abnormal fragility of bones. The sclera of the eye is often abnormally thin and translucent and may appear blue owing to a deficiency of connective tissue. Eight types (I-VIII) of this condition have been recognized. Types I to IV are caused by mutations in the COL1A1orCOL1A2genes or both. Type I is mild, but type II is severe and infants born with the condition usually do not survive, and types III and IV are progressive and/or deforming. Over 100 mutations in these two genes have been documented and include partial gene deletions and duplications. Other mutations affect RNA splicing, and the most frequent type results in the replacement of glycine by another bulkier amino acid, affecting formation of the triple helix. In general, these mutations result in decreased expression of collagen or in structurally abnormal pro chains that assemble into abnormal fibrils, weakening the overall structure of bone. When one abnormal chain is present, it may interact with two normal chains, but folding may be prevented, resulting in enzymatic degradation of all of the chains. This is called “procollagen suicide” and is an example of a dominant negative mutation, a result often seen when a protein consists of multiple different subunits. Types V to VIII are less common and are caused by mutations in the genes for proteins involved in bone mineralization other than collagen.

Osteopetrosis (marble bone disease), characterized by increased bone density, is a rare condition characterized by inability to resorb bone. It is due to mutations in the gene (located on chromosome 8q22) encoding carbonic anhydrase II (CA II), one of four isozymes of carbonic anhydrase present in human tissues. Deficiency of CA II in osteoclasts prevents normal bone resorption, and osteopetrosis results.

Osteoporosis is a generalized progressive reduction in bone tissue mass per unit volume, caused by an imbalance between bone resorption and deposition, and leads to skeletal weakness. The primary type 1 condition commonly occurs in women after the menopause. This is thought to be mainly due to lack of estrogen, which leads to increased bone resorbtion accompanied by decreased bone mineralization. Primary type 2 or senile osteoporosis occurs in both sexes post 75 years, although is more prevalent in women (ratio 2:1 female: male). The ratio of mineral to organic elements is unchanged in the remaining normal bone. Fractures of various bones, such as the head of the femur, occur very easily and represent a huge burden to both the affected patients and to society in general.

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مؤتمر السيد المجاهد يشهد عرض فيلم وثائقي عن سيرته العلمية ومشروع إحياء تراثه

بحث حوزوي يتناول التمييز بين المعجزة والسحر عند السيد المجاهد

بحث يناقش أثر القواعد العقلية في استنباط الأحكام الشرعية عند السيد محمد المجاهد

بحث علمي يناقش ردود السيد المجاهد على اللغويين والنحويين في كتابه (مفاتيح الأصول)

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الآخبار الصحية

هل توقيت نشاطك اليومي يؤثر على صحة دماغك؟.. العلماء يجيبون

"مشروب محبوب" يخفي فوائد لا يعرفها كثيرون

طبيب يكشف 5 أنواع للسعال.. بعضها خطير

نقص فيتامينات "خفي".. قد يفسّر التعب والتنميل وقلة التركيز

المزيد

الآخبار التكنلوجية

دراسة: تغيّرات في أسلوب القيادة قد تكشف مبكرا عن الخرف !

عمرها 773 ألف سنة.. اكتشاف أقدم أحافير بشرية في المغرب

"اختراق علمي".. اختبار دم في منزلك قد يكشف ألزهايمر

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مواضيع ذات صلة

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Transport Vesicle Formation and Function Involves SNAREs & Other Factors

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The ER Functions as The Quality Control Compartment of The Cell

Proteins Follow Several Routes to be Inserted Into or Attached to The Membranes of The Endoplasmic Reticulum

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Proteins Imported Into Peroxisomes Carry Unique Targeting Sequences

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Many proteins are targeted by signal sequences to their correct destinations

Conjugation reactions in phase 2 metabolism prepare Xenobiotics for excretion