Beta-adrenergic hyperresponsiveness in compensated hypothyroidism associated with Down syndrome

Area of Science:

• Endocrinology
• Genetics
• Cellular Biology

Background:

• Compensated hypothyroidism (CH) is common in Down syndrome (DS), but its cause is unknown.
• DS is also linked to gonadal failure, suggesting a shared underlying pathway.
• Previous studies indicated altered G-protein adenylate-cyclase (AC) system and beta-adrenergic responsiveness in DS.

Purpose of the Study:

• To investigate the role of the G-protein adenylate-cyclase (AC) system and beta-adrenergic responsiveness in compensated hypothyroidism in Down syndrome.
• To explore a potential unifying signal-transduction pathway for DS-associated endocrinopathies.

Main Methods:

• Studied 21 DS patients (11 with elevated TSH [hTSH], 10 with normal TSH [nTSH]) and 14 controls.
• Measured cAMP levels in peripheral mononuclear cells (PMCs) after stimulation with G-protein modulators (PGE1, CTx), an AC stimulator (forskolin), and a beta-adrenergic agonist (isoproterenol).

Main Results:

• cAMP responses to forskolin, PGE1, and CTx were similar across all groups.
• Isoproterenol-stimulated cAMP levels were significantly higher in the DS hTSH group compared to the DS nTSH group and controls (p=0.02).
• Four patients in the DS hTSH subgroup exhibited impaired sexual development.

Conclusions:

• A subgroup of DS patients with compensated hypothyroidism demonstrates hyperresponsiveness to beta-adrenergic stimulation in PMCs.
• This finding suggests a potential mechanism involving altered cellular signaling that could contribute to CH in DS.
• The observed hyperresponsiveness may impact thyroid gland function and TSH responsiveness, leading to CH.