Familial Dysalbuminemic Hyperthyroxinemia

Introduction
Newer analogue free T4 methods, despite claims to the contrary, are still prone to interference by commonly occurring polymorphic albumin variants. These albumin variants bind T4 with increased affinity. Free T4 methods typically return high values for free T4, usually with normal values for TSH. The degree of elevation is method dependant, although most methods can show some degree of interference. As three common genetic variants in the albumin gene are associated with increased affinity for T4, these can be simply detected using genetic methods.

Clinical Indications
Suspected thyroid hormone assay interference particularly unexpectedly raised free T4 with normal TSH. 

See also ‘Anomalous thyroid function tests’ for screening test.

Method Information
PCR and Dideoxy terminator sequencing of DNA extracted from peripheral leukocytes. Exon 3 and 7 are amplified and sequenced to detect p.R242H, p.R242P and p.L90P. Reference sequence NM_000477.3. +1 = ATG translation initiation codon.

Patient Preparation
As for all genetic tests patients need to be counselled. Dysalbuminaemic hyperthyroxinaemia is doinnantly inherited, so first degree relatives may also be affected. The requesting clinician is responsible for provision of appropriate counselling.

Sample Requirements
5mls of EDTA anti-coagulated blood are required.

Sample Handling
Please send the sample via first class post from UK locations

Interpretation
The laboratory will provide interpretation

Quality Assessment
UK EMQN.

Centres offering this assay
Cambridge Addenbrooke’s Hospital Endocrine Laboratory

References
OMIM +103600
Sapin R, Gasser F, Schlienger JL. Familial dysalbuminemic hyperthyroxinemia and thyroid hormone autoantibodies: interference in current free thyroid hormone assays. Horm Res. 1996;45(3-5):139-41.

 

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