The ratio of serum free triiodothyronine to free thyroxine in children: a retrospective database survey of healthy short individuals and patients with severe thyroid hypoplasia or central hypothyroidism

Background

The ratio of serum free triiodothyronine (FT3) to free thyroxine (FT4) has been shown to be constant in healthy adults. However, this ratio has been found to be decreased in athyreotic adult patients on levothyroxine (L-T4) supplementation. In order to better evaluate thyroid-related pathologies in children as well as to establish a reference range, we investigated the FT3/FT4 ratio in a pediatric population. Furthermore, we evaluated this ratio in children with congenital hypothyroidism as well as those with central hypothyroidism.

Methods

A reference range for the FT3/FT4 ratio was obtained from 129 Japanese children (3–17 y) with idiopathic short stature who were designated as the ‘Control’ group. Patients with congenital hypothyroidism due to athyreosis or severe thyroid hypoplasia (designated as ‘A/Hypoplasia’), as well as patients with central hypothyroidism (‘Central’), were recruited from the institutional database. For each group, the mean FT3/FT4 ratio was obtained.

Results

In the Control group, the FT3/FT4 ratio was 3.03 ± 0.38 10⁻² pg/ng (mean ± standard deviation) with no age or gender differences. A/Hypoplasia patients showed a significantly decreased mean FT3/FT4 ratio (2.17 ± 0.33, P < 0.001) compared to Control patients, with decreased FT3 and elevated FT4 levels. The Central group also showed a significantly decreased FT3/FT4 ratio (2.55 ± 0.45, P < 0.001) compared to the Control group, with decreased FT3 and equivalent FT4 levels.

Conclusions

The FT3/FT4 ratio appears to be constant between the ages of 3–17 y. Children on L-T4 due to congenital thyroid a/hypoplasia or central hypothyroidism have a decreased FT3/FT4 ratio compared to short normal children.

Mutational Analysis of Androgen Receptor (AR) Gene in 46,XY Patients with Ambiguous Genitalia and Normal Testosterone Secretion: Endocrinological Characteristics of Three Patients with AR Gene Mutations

The prevalence of abnormalities in androgen receptor gene (AR) among patients with ambiguous genitalia is unknown. Moreover, endocrinological data from prepubertal patients with AR mutation are very limited. Thus, the aim of this study was to examine the prevalence of abnormalities in AR among patients with both ambiguous genitalia, which was defined as a combination of two or more genital abnormalities (i.e. hypospadias, microphallus (penile length < 25 mm), hypoplastic scrotum, bifid scrotum, undescended testis) in this study, and normal to elevated T levels. We also compared the endocrinological data of prepubertal patients with AR mutation and ambiguous genitalia with that of those without the AR mutation. We screened 26 Japanese prepubertal 46,XY patients (five from three families were included) with both ambiguous genitalia and normal to elevated T levels. Mutations in AR were found in three (two of the three were related). Among the 23 patients without mutation in AR, the steroid 5-alpha-reductase 2 gene (SRD5A2) was also examined in eight patients with elevated T/dehydrotestosterone ratio after the hCG (>10) or with undervirilized family members. No mutation in SRD5A2 was found. Characteristics of the three patients with mutation in AR were compared with the 23 patients without mutation. In two patients, basal T levels (0.3, 0.2 ng/ml) and peak T levels after the hCG tests (8.3, 8.5 ng/ml) tended to be higher, and the peak LH/ peak FSH ratios after the GnRH tests (4.6, 4.0) were higher than in patients without mutation, at the ages of 1 yr and 9 mo and 3 yr and 8 mo, respectively. In conclusion, an abnormality in either AR or SRD5A2 was not common among patients with ambiguous genitalia and normal testosterone secretion. Elevated peak LH/peak FSH ratio (≥4) after the GnRH test in addition to detectable basal T levels and elevated peak T levels after the hCG test may infer AR abnormality in prepubertal patients with ambiguous genitalia at the age of one and over, although further study is needed, because our data were limited.

Gonadal Function in 15 Patients Associated with WT1 Gene Mutations

Denys-Drash syndrome (DDS) and Frasier syndrome (FS) are caused by mutations of the WT1 gene. These disorders are characterized by renal disease, abnormality of male sex differentiation, and Wilms' tumor and gonadoblastoma. There have been few reports on gonadal function in a large series of patients with mutations of the WT1 gene. Here, we evaluated the relation between gonadal function and the phenotype of external genitalia in 15 Japanese patients with WT1 mutations. We confirmed three sets of information. First, if a diagnosis of DDS and FS is arrived at by genetic analysis, there are some overlaps in the phenotypes of external genitalia and renal complications. Second, the responses of serum T for the human CG (HCG) loading test coincided with the phenotype of external genitalia in both DDS and FS, except two patients. One DDS patient had male type external genitalia with a low level of serum T response, and one FS patient had complete female external genitalia despite a definite serum T response to HCG stimulation. Third, four FS patients had incomplete development of pubic hair, together with low DHEA-S levels.