Catch-up Growth and Discontinuation of Fludrocortisone Treatment in Aldosterone Synthase Deficiency

BACKGROUND

Aldosterone synthase deficiency (ASD) caused by mutations in the CYP11B2 gene is characterized by isolated mineralocorticoid deficiency. Data are scarce regarding clinical and biochemical outcomes of the disease in the follow-up.

OBJECTIVE

Assessment of the growth and steroid profiles of patients with ASD at the time of diagnosis and after discontinuation of treatment.

DESIGN AND METHOD

Children with clinical diagnosis of ASD were included in a multicenter study. Growth and treatment characteristics were recorded. Plasma adrenal steroids were measured using liquid chromatography-mass spectrometry. Genetic diagnosis was confirmed by CYP11B2 gene sequencing and in silico analyses.

RESULTS

Sixteen patients from 12 families were included (8 females; median age at presentation: 3.1 months, range: 0.4 to 8.1). The most common symptom was poor weight gain (56.3%). Median age of onset of fludrocortisone treatment was 3.6 months (range: 0.9 to 8.3). Catch-up growth was achieved at median 2 months (range: 0.5 to 14.5) after treatment. Fludrocortisone could be stopped in 5 patients at a median age of 6.0 years (range: 2.2 to 7.6). Plasma steroid profiles revealed reduced aldosterone synthase activity both at diagnosis and after discontinuation of treatment compared to age-matched controls. We identified 6 novel (p.Y195H, c.1200 + 1G > A, p.F130L, p.E198del, c.1122-18G > A, p.I339_E343del) and 4 previously described CYP11B2 variants. The most common variant (40%) was p.T185I.

CONCLUSIONS

Fludrocortisone treatment is associated with a rapid catch-up growth and control of electrolyte imbalances in ASD. Decreased mineralocorticoid requirement over time can be explained by the development of physiological adaptation mechanisms rather than improved aldosterone synthase activity. As complete biochemical remission cannot be achieved, a long-term surveillance of these patients is required.

Fission yeast Schizosaccharomyces pombe as a new system for the investigation of corticosterone methyloxidase deficiency-causing mutations

The aldosterone synthase, CYP11B2, catalyses the conversion of 11-deoxycorticosterone to aldosterone, a process that requires three steps: a hydroxylation at position 11β to form corticosterone, another one at position 18 to produce 18-hydroxycorticosterone, and, finally, an oxidation at position 18 to form aldosterone. Aldosterone synthase deficiency usually finds its expression in infancy as a life-threatening electrolyte imbalance, caused by mutations in the CYP11B2 gene. Therefore, in depth studies of mutations and their enzymatic activities will provide information for the diagnosis and management of hypoaldosteronism caused by CYP11B2 deficiencies. Here, we report the development of a fast and cheap whole-cell technology for the enzymatic characterisation of CYP11B2 mutations. The principle of the new system is the heterologous expression of the mutants of CYP11B2 in fission yeast (Schizosaccharomyces pombe) followed by steroid bioconversion assays for the enzymatic characterisation of the investigated mutants. The new system was validated and 10 known mutations of CYP11B2 have been investigated, two of them for the first time concerning their effect on the CYP11B2 three-step reaction. The results of the fission yeast system were in good agreement with the cell culture results presenting this new system as an alternative non radioactive method that can be applied for the enzymatic characterisation of CYP11B2 mutations.

A missense mutation (GGC[435Gly]-->AGC[Ser]) in exon 8 of the CYP11B2 gene inherited in Japanese patients with congenital hypoaldosteronism

OBJECTIVES

To clarify the underlying molecular mechanism of corticosterone methyl oxidase type II (CMO II) deficiency, Japanese patients newly diagnosed with CMO II deficiency were investigated.

METHODS

We analyzed the patients' genomic DNA sequence on all 9 exons of the CYP11B2 gene. In addition, restriction fragment length polymorphism (RFLP) analysis and expression studies were performed.

RESULTS

The analysis showed that the patients homozygously retained a missense mutation, Gumacr;GC[435Gly]-->Aumacr;GC[Ser], in the CYP11B2 gene. Expression studies indicated that the steroid 18-hydroxylase/oxidase activities of the mutant enzyme were substantially reduced.

CONCLUSION

These results support the hypothesis that this mutation causes CMO II deficiency in the patients, and are in accordance with our theory that the partial loss of P-450(C18) activities causes CMO II deficiency.

Reduced Na+, K(+)-ATPase activity in patients with pseudohypoaldosteronism

Pseudohypoaldosteronism is a hereditary salt-wasting syndrome usually seen in infancy with weight loss, dehydration, and failure to thrive. The pathophysiologic origin of pseudohypoaldosteronism is unknown. The defect could be related to the unresponsiveness of target organs to mineralocorticoids resulting in hyponatremia, hyperkalemia, and markedly elevated plasma aldosterone and renin levels. Red blood cell Na+, K(+)-ATPase activity was measured in a pair of twins with pseudohypoaldosteronism, in an unrelated child with hypoaldosteronism, and in an age-matched group of 50 healthy infants and young children. The enzyme was assayed by a method that couples ATP hydrolysis with NADH oxidation. Plasma renin and aldosterone levels were measured by RIA. Red blood cell Na+, K(+)-ATPase activity in the twins with pseudohypoaldosteronism was very low at the time of diagnosis (3 wk). In both twins a time-related gradual increase in enzyme activity was observed during the 1st mo of life, reaching control values between 6 and 8 mo of age. This increase was associated with both a reduction in salt requirement and clinical improvement. Plasma renin activity and aldosterone levels were very high at the time of diagnosis. Plasma renin activity reverted gradually to normal values, whereas aldosterone levels remained high throughout the follow-up period. The child with hypoaldosteronism had normal Na+, K(+)-ATPase activity at diagnosis and during follow-up.