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Retinal Photoreceptor Functions Are Compromised in Patients With Resistance to Thyroid Hormone Syndrome (RTHβ)
Irene Campi1,2, Gabriella Cammarata3, Stefania Bianchi Marzoli3
1Division of Endocrine and Metabolic Diseases, Laboratory of Endocrine and Metabolic Research, Istituto Di Ricovero e Cura a Carattere Scientifico, Istituto Auxologico Italiano, 20149 Milan, Italy.
Context:
In animal models, disruption of thyroid hormone (TH) receptor-β (TRβ) reduces the long/medium wavelength (L/M) and increases the short-wavelength (S) cones. Retinal photoreceptor (RP) functions are unknown in patients with resistance to TH syndrome (RTHβ) with dominant-negative TRβ mutations.
Objective:
To investigate RP functions in RTHβ.
Design, Setting, And Participants:
Case-control study involving 27 RTHβ patients and 31 age/sex-matched controls, conducted in two tertiary referral centers in Italy.
Main Outcome Measures:
Color vision sensitivity assessed by Farnsworth; central macular thickness (CMT) of the outer retinal layer measured by spectral-domain optical coherence tomography; and retinal function tested by full-field electroretinogram (ERG) and S-cone ERG.
Results:
Color sensitivity was worse in RTHβ patients than controls (P = 0.002). CMT was overlapping between the study groups but directly correlated with sex hormone-binding globuline levels in RTHβ. We found a significant reduction in amplitude of the cone (P = 0.024) and of the rod response (P = 0.006) in the ERG of RTHβ patients compared with controls. The response of the L/M cones measured by a specialized ERG test was lower in RTHβ than controls (P = 0.027), whereas no differences were found in the S-cone response. No correlations were found between TH levels, total error score, or electrophysiological results. Furthermore, no differences were found between patients with maternal or de novo/paternal inheritance.
Conclusions:
We report, to our knowledge, the first in vivo evidence of functional defects of RP in RTHβ. These changes occur independently of endogenous TH levels or the prenatal exposure to high or normal maternal TH.