Short metacarpal and metatarsal bones

Introduction Short metacarpal and humerus are the main clinical manifestations of hypothyroidism in children. Insufficient PTH can weaken the role of osteoclasts, reduce bone calcium mobilization, and reduce the production of 1,25-(OH)2D3 and the reabsorption of calcium by renal tubules and the reduction of phosphorus excretion. High blood phosphorus, only a small number of oral antacids or blood phosphorus in the diet can be normal. The cause of the disease is a dominant X-chain-locked hereditary disease. Paying attention to pre-marital examination and focusing on reproductive health prevention and other measures to prevent genetic diseases is of great significance for the prevention and treatment of this disease.

Cause

(1) Causes of the disease

The disease is a different exogenous X-chain-locked hereditary disease. The basic obstacle is that the target cells do not respond completely or completely to PTH. This abnormality in PTH response involves a series of reactions from the binding of PTH to the receptor into the target cell, and the currently known defect: in the red blood cells of this patient, coupled with the PTH receptor adenylate cyclase system Linkage; a regulatory protein that is sensitive to avian nucleotides. The target organ tissue is not responsive to PTH. Or parathyroid hormone abnormal structure, not recognized by the PTH receptor to bind to it; PTH promotes the role of 1,25 (OH) 2D in the kidney is also abnormal, so that PTH can not play a role.

(two) pathogenesis

Parathyroid tissue is normal, PTH secretion is normal, blood PTH is normal or high, but there is still hypocalcemia and hyperphosphatemia. Parathyroid compensatory hypertrophy is the target organ cell weakened or completely lack of PTH response. . Generally divided into type 2, pseudo-parathyroidal low type I, is a receptor defect on the target cell membrane, can not accept PTH, can accept but can not activate adenylyl cyclase system, can not synthesize cAMP, give PTH urinary excretion cAMP does not increase Thus PTH cannot exert physiological effects. Injection of exogenous PTH, low blood calcium, high blood phosphorus is still not corrected. Pseudo-parathyroidal type II is an increase in cAMP in the urinary tract after injection of exogenous PTH, but phosphorus excretion does not increase, hypocalcemia and hyperphosphatemia are not corrected, and are post-receptor defects. The disease is a dominant hereditary X-chain-locked inheritance.

an examination

Related inspection

Serum calcium (Ca2+, Ca) serum phosphorus (Pi) bone and joint plain film of limbs

Clinical features: In addition to low hypocalcemia near the nail, there are congenital bones and other developmental deformities, such as dwarfism, round face, mental retardation, small jaw, neck short, heterotopic ossification, etc., such as kidney In response to bone tissue response to PTH, subperiosteal absorption, fibrocystic osteitis, known as fibrotic osteitis pseudo-parathyroid.

The child has sputum, short stature, short thumb, short 1, 2, 4 metacarpal and humerus, occasionally the second finger is longer than the middle finger, short toe, exogenous epiphysis, thickening of the skull and growth disorders, common There are translocation calcium deposition and subcutaneous migration osteogenesis, basal ganglia calcification and crystalline cataract. Children often have the above anatomical features. PTH resistance can also be accompanied by hypogonadal function, also caused by Gs gene mutation, blood calcium reduction, phosphorus And alkaline phosphatase can be elevated, blood PTH increased or normal.

an examination:

1. Blood biochemical examination: blood calcium is lowered and blood phosphorus is increased.

2. Ellsworth-Howard test: After administration of 200 U (2 ml) of PTH (injection), if the urinary phosphorus is discharged 5 to 6 times more than the original, it means that the primary hypoparathyroidism is reduced, that is, the renal tubules have good PTH. reaction. If it is less than 2 times, it is the disease. If the cAMP can be measured at the same time, if the cAMP is increased, and the urinary phosphorus is more, the primary hypoparathyroidism is reduced. For example, only cAMP is increased, and the intrinsic type II indicates that the second messenger is destroyed, such as urinary phosphorus. And cAMP does not increase is intrinsic type I (Drezner classification: type I with PTH no matter urinary phosphorus and cAMP are not increased; type II is urinary phosphorus is not increased, but cAMP increased).

3. X-ray bone examination: visible various deformities, such as short finger toe deformity, skull thickening, exostosis, heterotopic ossification, and fibrous osteitis.

4. EEG examination: abnormal brain waves can be found.

Differential diagnosis

The metacarpal index is equal to the sum of the 2nd and 5th metacarpal lengths and the 2nd and 5th metacarpal transverse diameters. The metacarpal bone, the bone of the palm, starts with the thumb and is the first, second, third, fourth, and fifth metacarpals. The clinical manifestations of Marfan syndrome are an increase in both the metacarpal index and the phalanx index.

The carpal bone dysplasia and the metacarpal bone are rod-like changes: the symptoms are found in the mucopolysaccharidosis type VI, which is also known as Maroteaux-Lamy syndrome, multiple dystrophic dwarfism. It is an autosomal recessive hereditary disease. The disease is autosomal recessive. The basic biochemical defect of this disease is the reduction of N-acetylgalactosamine-4-sulfatase activity, which can hydrolyze the sulfuric acid in N-acetylgalactosamine-sulfate, which occurs in chondroitin-4- Sulfuric acid also occurs in dermatan sulfate. The gene is located at 5q12 to q13 and may have 2 alleles. In this type of human body, due to the insufficient activity of the enzyme, chondroitin-4-sulfate and dermatan sulfate can be deposited in various tissue cells to cause disease.

Excessive keratosis: refers to local skin keratinization, dry skin, scaly, chapped, generally no subjective discomfort, sometimes itching or pain, often aggravated in winter.

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