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Syndrome presenting with round face, short stature, short neck, and obesity. Subcutaneous and intracranial calcifications, seizures, and neuromuscular problems such as fatigue and muscle cramps. Pseudohypoparathyroidism and hypocalcemia.

Albright hereditary osteodystrophy

This infant with obesity, round face, and short neck shows some of the typical features of this disorder.

Pseudohypoparathyroidism Type IA. Strictly, Albright Hereditary Osteodystrophy relates to type IA only. However, for completeness, Pseudohypoparathyroidism Type IB is included here. Do not confuse Albright Hereditary Osteodystrophy with McCune-Albright Syndrome.

Exact incidence is unknown; however, in Japan the incidence is estimated to range from 3 to 4 per 1,000,000 live births.

Autosomal dominant inheritance. In type IA, the genetic defect involves the α subunit of the stimulatory G protein (which is either defect or only produced in minimal amounts) that couples pathways for transmembrane signaling and enhances the production of cyclic adenosine monophosphate (cAMP). The gene encoding for this α subunit of the G protein (GNAS1) has been mapped to the long arm of chromosome 20 (20q13.2). Occasionally, a small terminal deletion on chromosome 2 may exist. Full expression occurs in patients with maternal transmission, whereas only partial expression occurs in paternally transmitted cases. All patients are heterozygous, leaving them with one normal allele for the α subunit, which is not only required for parathormone, but also for many other peptide hormones (e.g., adrenocorticotropin [ACTH], thyrotropin, glucagon, gonadotropins, antidiuretic hormone). Consequently, these patients may clinically exhibit some resistance to the effects of all these hormones. Although type IB also is autosomal dominant inherited, the underlying defect is different. The mutation has been mapped to 20q13.3 (i.e., close to the GNAS1 gene region). Hormonal resistance appears to be caused by limited or absent responsiveness of the kidneys to parathormone. The skeletal lesions in these patients are evidence of an intact bone response to parathormone.

Increase in parathyroid hormone release and deficient end-organ responsiveness, either because of germline mutation in the gene encoding G α subunit, thus decreasing expression or function of G protein (type IA), or presumably a receptor defect (type IB).

Hypocalcemia associated with hyperphosphatemia occurs in type IA but not in type IB. The activity of protein G is reduced in type IA but is normal in type IB. Hyperparathyroidism in combination with hypocalcemia is caused by either secondary hyperparathyroidism or pseudohyperparathyroidism. Administration of exogenous parathormone is used to assess the renal and osseous response. The concentration changes of calcium, phosphate, calcitriol, and cAMP in the plasma and of phosphate and cAMP in the urine are measured. Serum concentration for estrogen is low but concentrations of Luteinizing Hormone (LH) and Follicular Stimulating Hormone (FSH) are high (reflecting involvement of G protein in the actions of all these hormones). CT scan of the head may reveal calcifications of the choroid ...

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