Albright hereditary osteodystrophy (AHO) is a syndrome with a wide range of manifestations including short stature, obesity, rounded face, subcutaneous ossifications and characteristic shortening and widening of long bones in the hands and feet (brachydactyly mostly affecting the 4th and 5th rays). Mental retardation was less frequently described. These somatic features are associated with resistance to PTH or parathyroid hormone (a syndrome called pseudohypoparathyroidism type 1a or PHP1a) and to other hormones (thyroid-stimulating hormone or TSH in particular). PHP1a is characterized by hypoparathyroid manifestations (hypocalcemia, hyperphosphoremia) and elevated PTH levels, indicating resistance to the hormone. Patients show decreased biological activity of the protein Gs in erythrocytes. AHO with Gs deficiency but without hormone resistance is called pseudopseudohypoparathyroidism (PPHP). OHA with hormonal resistance but normal Gs activity is called PHP-1c. PHP without AHO (and with normal levels of Gs biological activity) is generally classified as PHP-1b. AHO with decreased Gs activity is due to heterozygous inactivating mutations of the GNAS gene. This gene encodes the a-subunit of Gs, the heterotrimeric G protein that couples with heptahelical plasma membrane receptors. Whether the patient exhibits resistance to hormones or not is determined by the parental origin of the mutation, a functional maternal GNAS1 allele having a predominant role in preventing hormone resistance.
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