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Zorluk: Çok zorEndocrine and Metabolic Mechanisms

Match the following molecular or genetic lesions with their corresponding classic clinical and laboratory phenotype.

  • Inactivating mutation of GNAS1 inherited from the motherHypocalcemia, hyperphosphatemia, elevated parathyroid hormone, brachydactyly, and subcutaneous calcifications
  • Inactivating mutation of GNAS1 inherited from the fatherNormocalcemia, normal phosphate, normal parathyroid hormone, brachydactyly, and subcutaneous calcifications
  • Inactivating mutation of the calcium-sensing receptor (CaSR) geneMild asymptomatic hypercalcemia, low urinary calcium excretion, and normal to mildly elevated parathyroid hormone
  • Activating mutation of the calcium-sensing receptor (CaSR) geneHypocalcemia, hyperphosphatemia, hypercalciuria, and inappropriately low or normal parathyroid hormone
  • Mutation in the autoimmune regulator (AIRE) geneHypocalcemia, hyperphosphatemia, low parathyroid hormone, chronic mucocutaneous candidiasis, and adrenal insufficiency

Cevap

The correct pairings are: Maternal GNAS1 mutation matches with pseudohypoparathyroidism type 1A (PTH resistance and Albright hereditary osteodystrophy); Paternal GNAS1 mutation matches with pseudopseudohypoparathyroidism (normocalcemia with AHO phenotype); Inactivating CaSR mutation matches with familial hypocalciuric hypercalcemia; Activating CaSR mutation matches with autosomal dominant hypocalcemia; AIRE mutation matches with autoimmune polyendocrine syndrome type 1.
Each genetic lesion dictates a distinct pathophysiologic mechanism: GNAS1 is maternally expressed in the renal tubule, so only maternal mutations cause PTH resistance (PHP1A); paternal mutations only cause the somatic AHO phenotype (PPHP). CaSR inactivation mimics low calcium signaling, causing FHH, whereas activation mimics high calcium signaling, causing autosomal dominant hypocalcemia. AIRE mutations lead to autoimmune destruction of endocrine glands (APS-1).

Adım Adım Çözüm

1
Evaluate the GNAS1 mutations considering genomic imprinting.
Maternal transmission leads to renal PTH resistance (PHP1A), while paternal transmission leads to an isolated somatic phenotype (PPHP).
The GNAS1 gene is imprinted in the renal proximal tubule, exclusively expressing the maternal allele. Without the maternal allele, the kidney cannot respond to PTH.
2
Distinguish between activating and inactivating CaSR mutations.
Inactivating mutations mimic low calcium (causing FHH), while activating mutations mimic high calcium (causing autosomal dominant hypocalcemia).
CaSR normally suppresses PTH and promotes renal calcium excretion in response to high calcium. An activating mutation shifts this set-point to the left, suppressing PTH prematurely.
3
Identify the syndromic cause of immune-mediated hypoparathyroidism.
AIRE mutation is paired with the classic triad of autoimmune polyendocrine syndrome type 1.
Loss of central immune tolerance leads to autoimmune destruction of the parathyroid and adrenal glands alongside chronic fungal infections.

Anahtar Kavram

Molecular mechanisms, genomic imprinting, and receptor kinetics in calcium and phosphate homeostasis disorders.
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Konular

Endocrine and Metabolic Mechanisms

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