Gokhan Ozisik

The role of SF1 in adrenal and reproductive function: insight from naturally occurring mutations in humans

Steroidogenic factor 1 is a monomeric orphan nuclear receptor and one of several hundreds of transcription factors encoded in the human genome. It regulates the transcription of many genes involved in gonadal development, sexual differentiation, steroidogenesis and reproduction. Recently, mutations in the gene encoding SF1 have been identified in several patients with primary adrenal failure and 46,XY sex-reversal. Interpreting the consequences of these mutations provides further understanding of transcription factor haploinsufficiency in human genetic disease as well as the exquisite sensitivity of humans to gene-dosage effects during adrenal and gonadal development.

SF1 in the Development of the Adrenal Gland and Gonads

SF1 (steroidogenic factor-1; NR5A1) is an orphan nuclear receptor that is expressed in the adrenal gland, gonads, spleen, ventromedial hypothalamus and pituitary gonadotroph cells. Combined approaches of targeted mutagenesis in mice and examination of the effects of naturally occurring mutations in humans have clarified the role of SF1 in steroidogenesis and development. Targeted disruption of Sf1 (Ftzf1) in mice prevents gonadal and adrenal development and causes male-to-female sex reversal. A heterozygous loss-of-function human SF1 mutation (G35E) was described in a patient with adrenal failure and complete 46,XY sex reversal, indicating that haploinsufficiency of this transcription factor is sufficient to cause a severe clinical phenotype. In an infant with a similar clinical phenotype, a homozygous SF1 mutation (R92Q) was identified. In functional assays, this mutant SF1 protein exhibited partial loss of DNA binding and transcriptional activity when compared with the more severe G35E P-box mutant. These patients reveal the exquisite sensitivity of SF1-dependent developmental pathways to gene dosage and function in humans.

The effects of thyroid status on plasma leptin levels in women

Leptin, the product of the adipose specific ob gene, regulates food intake and energy expenditure. However, little is known about the effects of thyroid status on plasma leptin levels in women. We determined fasting plasma leptin levels before and 1 month after restoration of euthyroidism in 20 female patients with hypothyroidism, 20 female patients with hyperthyroidism and 20 age and BMI — matched female controls. To restore the normal thyroid function patients with hypothyroidism were treated with levothyroxine, whereas patients with hyperthyroidism were treated with propylthiouracil. Plasma leptin levels were measured by a RIA method with a sensitivity of 0.5 µg/l. Leptin levels were significantly lower in patients with hypothyroidism before treatment (4.17±2.58 µg/l) than in patients with hyperthyroidism (6.80±4.3 µg/l; z= −2.06, p=0.037). Leptin levels were significantly higher in hyperthyroid patients than in the control group (3.71±1.69 µ/l, z= −2.44, p=0.014) whereas leptin levels in the hypothyroid patients were not significantly different from those in control subjects (z= −0.16, p=0.87). Restoration of euthyroid state was not associated with a significant change in leptin levels either in the hypothyroid (from 4.17±2.58 to 5.22±3.4 µg/l; z= −1,74, p=0.08) or in the hyperthyroid group (from 6.80±4.37 µg/l to 7.93±6.25 µg/l z= −0.89, p=0.37), although a tendency for leptin to increase was observed in both groups. There was no correlation between plasma leptin and FT3, FT4, TSH, or BMI either before or after therapy in both groups. Leptin levels were significantly correlated with BMI in the control group (r= −0.53, p=0.018). We conclude that plasma leptin levels are increased in hyperthyroidism and unchanged in hypothyroidism. Furthermore, our study demonstrates that mean plasma leptin levels are not influenced by short term restoration of euthyroidism in both hypothyroidism and hyperthyroidism, although an effect of long-term treatment may not be excluded.

Mitochondrial DNA common deletion is not associated with thyroid, breast and colorectal tumors in Turkish patients

Recently, efforts have been focused on mitochondrial DNA changes and their relation to human cancers. Among them, a 4977 bp deletion of mitochondrial DNA, named “common deletion”, has been investigated in several types of tumors, with inconsistent results. In this study, we investigated the presence of the common deletion in tissues from 25 breast, 25 colorectal and 50 thyroid tumors and in the adjacent healthy tissues from Turkish patients. Samples from healthy volunteers were also evaluated for comparison. Two PCR-based methods were used for the detection of the common deletion. First, two pairs of primers were used to amplify wild-type and deleted mtDNA. Then, a highly sensitive nested-PCR was performed, to determine low amounts of deleted genomes. By the first method, wild-type mtDNAs were observed in all samples, but a deletion was observed in only six thyroid samples, by using the nested-PCR method. In conclusion, the mitochondrial common deletion was very rare in our study group and did not appear to be not related with cancer.

A novel single base deletion at codon 434 (1301delT) of the DAX1 gene associated with prepubertal testis enlargement

We have identified a novel DAX1 frameshift mutation (1301delT) at codon 434 in a patient with primary adrenal insufficiency. This 11-day-old boy was admitted to the hospital with hyponatremia, hyperkalemia, and suspected congenital adrenal abnormality. He exhibited severe hypoglycemia, pallor of the skin, buccal and genital hyperpigmentation, hypotension (90/45 mm Hg), anemia, and diarrhea. Although basal gonadotropins were low, and responded minimally to exogenous GnRH, the size of his testes began to increase at age 4 and reached 4.5 mL at the age of 9 years and 8 months. Testosterone levels were prepubertal. These findings further emphasize the variable clinical presentation in children with DAX1 gene mutations and indicate the value of genetic testing in boys with primary adrenal insufficiency.