Related Experiment Videos
Thyroxine-binding globulin deficiency detected by newborn screening
1Department of Pediatrics, Oregon Health Sciences University, Portland 97201.
Insights
Inherited thyroxine-binding globulin (TBG) deficiency is common in Northwest boys, affecting 1 in 1700. This X-linked disorder impacts thyroid hormone levels, but free T4 remains normal in affected infants.
Area of Science:
- Endocrinology
- Genetics
- Neonatal Screening
Background:
- Thyroxine-binding globulin (TBG) is crucial for thyroid hormone transport.
- Inherited TBG deficiency is an X-linked disorder affecting thyroid hormone levels.
- Neonatal screening programs identify infants with potential thyroid abnormalities.
Purpose of the Study:
- To determine the prevalence of inherited thyroxine-binding globulin (TBG) deficiency in infants.
- To assess the impact of TBG deficiency on thyroid hormone concentrations in newborns.
Main Methods:
- Analysis of data from the Northwest Regional Screening Program (1975-1991).
- Inclusion of infants with low T4 levels on filter paper tests.
- Measurement of serum T4, T3RU, and thyrotropin levels.
Main Results:
- TBG deficiency identified in 1:4315 infants overall (1:2400 for boys).
- Higher frequency observed in Oregon (1:3080), likely due to more comprehensive screening.
- TBG-deficient boys showed altered T4 and T3RU values; free T4 levels were normal.
- TBG deficiency is significantly more common in boys (male/female ratio 8.9:1).
Conclusions:
- Inherited TBG deficiency is a relatively common condition in Northwest boys.
- The disorder causes significant alterations in total T4 and T3RU but not free T4.
- Screening programs can identify this genetic condition, which requires careful interpretation of thyroid function tests.
Abstract:
We examined the results of the Northwest Regional Screening Program from May 1975 to June 1991 to determine the prevalence of inherited thyroxine-binding globulin (TBG) deficiency and its effect on thyroid hormone concentrations in infants. Serum thyroxine (T4), triiodothyronine resin uptake (T3RU), and thyrotropin values were requested of physicians caring for all infants with a single filter paper T4 level < 38.6 nmol/L (3 micrograms/dl) or a T4 level < 3rd percentile on two filter paper tests (at birth and 2 to 6 weeks of age). From 1,367,724 infants screened in five states, TBG deficiency, an X-linked disorder, was identified in 317 infants (285 boys). For the entire screening program the calculated frequency of TBG deficiency was 1:4315 infants (1:2400 for boys). In Oregon, where 95% of infants have two screening tests performed, the calculated frequency was somewhat higher (1:3080 infants; 1712 boys) and is probably more accurate. The mean serum T4 concentration for TBG-deficient boys was 41.9 nmol/L (3.26 micrograms/dl); 31% had values < 25.7 nmol/L (2.0 micrograms/dl). The mean serum T4 concentration for TBG-deficient girls was 60.2 nmol/L (4.68 micrograms/dl), with none < 2.0 micrograms/dl. The mean T3RU value was 0.472 in TBG-deficient boys, and 0.412 in TBG-deficient girls; the T3RU value was > 0.55 in 24% of TBG-deficient boys but was > 0.55 in only one girl. Free serum T4 levels were normal in all 56 TBG-deficient infants studied, and TBG levels were low in all 20 infants studied. Inherited TBG deficiency is common in boys in the Northwest, with a frequency of 1:1700 and a male/female ratio of 8.9:1. Boys with TBG deficiency have mild, moderate, or severe alterations in total T4 and T3RU values, but severe deficiency is rare in girls.