Nicotinamide nucleotide transhydrogenase mutation analysis in Chinese patients with thyroid dysgenesis

Lack of NAD(P)+ transhydrogenase activity in patients with primary adrenal insufficiency due to NNT variants

BACKGROUND

Pathogenic variants in the nicotinamide nucleotide transhydrogenase gene (NNT) are a rare cause of primary adrenal insufficiency (PAI), as well as functional impairment of the gonads.

OBJECTIVE

Despite the description of different homozygous and compound heterozygous NNT variants in PAI patients, the extent to which the function and expression of the mature protein are compromised remains to be clarified.

DESIGN

The activity and expression of mitochondrial NAD(P)+ transhydrogenase (NNT) were analyzed in blood samples obtained from patients diagnosed with PAI due to genetically confirmed variants of the NNT gene (n = 5), heterozygous carriers as their parents (n = 8), and healthy controls (n = 26).

METHODS

NNT activity was assessed by a reverse reaction assay standardized for digitonin-permeabilized peripheral blood mononuclear cells (PBMCs). The enzymatic assay was validated in PBMC samples from a mouse model of NNT absence. Additionally, the PBMC samples were evaluated for NNT expression by western blotting and reverse transcription quantitative polymerase chain reaction and for mitochondrial oxygen consumption.

RESULTS

NNT activity was undetectable (<4% of that of healthy controls) in PBMC samples from patients, independent of the pathogenic genetic variant. In patients' parents, NNT activity was approximately half that of the healthy controls. Mature NNT protein expression was lower in patients than in the control groups, while mRNA levels varied widely among genotypes. Moreover, pathogenic NNT variants did not impair mitochondrial bioenergetic function in PBMCs.

CONCLUSIONS

The manifestation of PAI in NNT-mutated patients is associated with a complete lack of NNT activity. Evaluation of NNT activity can be useful to characterize disease-causing NNT variants.

Familial Glucocorticoid Deficiency Presenting with Tonic-Clonic Seizure: A Case Report

INTRODUCTION

Familial glucocorticoid deficiency (FGD) is a rare cause of adrenal insufficiency in children. The condition can present with features of low cortisol and high adrenocorticotropic hormone (ACTH). Late diagnosis can be associated with high morbidity and high mortality rates.

PATIENT

The presented case was a three-year-old Saudi girl who presented with dehydration and seizures as a complication of hypoglycemia. The initial examination and investigations revealed hyperpigmentation and normal arterial blood pressure. The lab investigation and genetic study revealed hypoglycemia, metabolic acidosis, low serum cortisol: 53 nmol/L (N: 140-690 nmol/L), normal androgens: 0.65 nmol/L (N: 0.5-2.4 nmol/L) and aldosterone: 50 pgmL (N: 2-200 pg/mol), and normal serum electrolytes. The ACTH level was more than 2000 pg/mL. A genetic study indicated a homozygous likely variant in the nicotinamide nucleotide transhydrogenase (NNT) gene, consistent with a genetic diagnosis of autosomal recessive glucocorticoid deficiency type 4. No mutations were found regarding MC2R, MRAP, and TXNRD2.

INTERVENTION AND OUTCOME

The child was started on hydrocortisone, initially at 100 mg/m²/dose IV and then 100 mg/m²/day divided to q 6 hr. The dose was gradually decreased to 15 mg/m²/day PO BID, with clinical improvement and normalization of the serum ACTH level.

CONCLUSIONS

The autosomal recessive glucocorticoid deficiency, a variant of FGD type 4, is a very rare condition that may lead to high rates of mortality when the diagnosis and treatment occur late. Therefore, early diagnosis and treatment is essential for good outcomes.

Iodine as a potential endocrine disruptor-a role of oxidative stress

PURPOSE

Iodine is an essential micronutrient required for thyroid hormone biosynthesis. However, overtreatment with iodine can unfavorably affect thyroid physiology. The aim of this review is to present the evidence that iodine-when in excess-can interfere with thyroid hormone synthesis and, therefore, can act as a potential endocrine-disrupting chemical (EDC), and that this action, as well as other abnormalities in the thyroid, occurs-at least partially-via oxidative stress.

METHODS

We reviewed published studies on iodine as a potential EDC, with particular emphasis on the phenomenon of oxidative stress.

RESULTS

This paper summarizes current knowledge on iodine excess in the context of its properties as an EDC and its effects on oxidative processes.

CONCLUSION

Iodine does fulfill the criteria of an EDC because it is an exogenous chemical that interferes-when in excess-with thyroid hormone synthesis. However, this statement cannot change general rules regarding iodine supply, which means that iodine deficiency should be still eliminated worldwide and, at the same time, iodine excess should be avoided. Universal awareness that iodine is a potential EDC would make consumers more careful regarding their diet and what they supplement in tablets, and-what is of great importance-it would make caregivers choose iodine-containing medications (or other chemicals) more prudently. It should be stressed that compared to iodine deficiency, iodine in excess (acting either as a potential EDC or via other mechanisms) is much less harmful in such a sense that it affects only a small percentage of sensitive individuals, whereas the former affects whole populations; therefore, it causes endemic consequences.

Thyroid hypogenesis is associated with a novel AKT3 germline variant that causes megalencephaly and cortical malformation

The molecular mechanisms involved in thyroid organogenesis have not been fully elucidated. We report a patient with a de novo germline AKT3 variant, NM_005465.7:c.233A > G, p.(Gln78Arg), who presented with congenital hypothyroidism in addition to typical AKT3-related brain disorders. The report of this patient contributes to delineating the associated yet uncertain endocrine complications of this AKT3 disease-causing variant.