Latin-American consensus on the transition into adult life of patients with X-linked hypophosphatemia

INTRODUCTION

X-linked hypophosphatemia is an orphan disease of genetic origin and multisystem involvement. It is characterized by a mutation of the PHEX gene which results in excess FGF23 production, with abnormal renal and intestinal phosphorus metabolism, hypophosphatemia and osteomalacia secondary to chronic renal excretion of phosphate. Clinical manifestations include hypophosphatemic rickets leading to growth abnormalities and osteomalacia, myopathy, bone pain and dental abscesses. The transition of these patients to adult life continues to pose challenges to health systems, medical practitioners, patients and families. For this reason, the aim of this consensus is to provide a set of recommendations to facilitate this process and ensure adequate management and follow-up, as well as the quality of life for patients with X-linked hypophosphatemia as they transition to adult life.

MATERIALS AND METHODS

Eight Latin American experts on the subject participated in the consensus and two of them were appointed as coordinators. The consensus work was done in accordance with the nominal group technique in 6 phases: (1) question standardization, (2) definition of the maximum number of choices, (3) production of individual solutions or answers, (4) individual question review, (5) analysis and synthesis of the information and (6) synchronic meetings for clarification and voting. An agreement was determined to exist with 80% votes in favor in three voting cycles.

RESULTS AND DISCUSSION

Transition to adult life in patients with hypophosphatemia is a complex process that requires a comprehensive approach, taking into consideration medical interventions and associated care, but also the psychosocial components of adult life and the participation of multiple stakeholders to ensure a successful process. The consensus proposes a total of 33 recommendations based on the evidence and the knowledge and experience of the experts. The goal of the recommendations is to optimize the management of these patients during their transition to adulthood, bearing in mind the need for multidisciplinary management, as well as the most relevant medical and psychosocial factors in the region.

Long-term effects of hypercalcemia in kidney transplant recipients with persistent hyperparathyroidism

BACKGROUND

Hypercalcemia is highly prevalent in kidney transplant recipients with hyperparathyroidism. However, its long-term impact on graft function is uncertain.

METHODS

We conducted a prospective cohort study investigating adverse graft outcomes associated with persistent hypercalcemia (free calcium > 5.2 mg/dL in ≥ 80% of measures) and inappropriately elevated intact parathyroid hormone (> 30 pg/mL) in kidney transplant recipients. Asymptomatic mild hypercalcemia was monitored unless complications developed.

RESULTS

We included 385 kidney transplant recipients. During a 4-year (range 1-9) median follow-up time, 62% of kidney transplant recipients presented persistent hypercalcemia. Compared to kidney transplant recipients without hypercalcemia, there were no significant differences in graft dysfunction (10% vs. 12%, p = 0.61), symptomatic urolithiasis (5% vs. 3%, p = 0.43), biopsy-proven calcium deposits (6% vs. 5%, p = 1.0), fractures (6% vs. 4%, p = 0.64), and a composite outcome of urolithiasis, calcium deposits, fractures, and parathyroidectomy indication (16% vs. 13%, p = 0.55). In a subset of 76 kidney transplant recipients, subjects with persistent hypercalcemia had higher urinary calcium (median 84 [43-170] vs. 38 [24-64] mg/day, p = 0.03) and intact fibroblast growth factor 23 (median 36 [24-54] vs. 27 [19-40] pg/mL, p = 0.04), and lower 25-hydroxyvitamin D levels (11.3 ± 1.2 vs. 16.3 ± 1.4 ng/mL, p < 0.001). In multivariate analysis, pretransplant intact parathyroid hormone < 300 pg/mL was associated with a reduced risk of post-transplant hypercalcemia (OR 0.51, 95% CI 0.32-0.80).

CONCLUSIONS

Long-term persistent mild hypercalcemia (tertiary hyperparathyroidism) was frequent in kidney transplant recipients in our series. This condition presented with lower phosphate and 25-hydroxyvitamin D, and higher urinary calcium and intact fibroblast growth factor 23 levels compared to kidney transplant recipients without hypercalcemia, resembling a mild form of primary hyperparathyroidism. Despite these metabolic derangements, the risk of adverse graft outcomes was low.

Vitamin D Hydroxylation-deficient Rickets Type 1A Misdiagnosed as Normocalcemic Primary Hyperparathyroidism

Vitamin D hydroxylation-deficient rickets type 1A is an autosomal recessive disorder caused by pathogenic variants in CYP27B1 gene, which encodes for 1α-hydroxylase, the enzyme responsible for the conversion of 25-OH vitamin D into its active form 1,25(OH)2 vitamin D. We report the case of a 3-year-old female Mexican patient with growth retardation and progressive bone deformity, whose laboratory studies showed 25-OH vitamin D deficiency, a normal serum calcium and an elevated intact parathyroid hormone level that remained high despite calcitriol, cholecalciferol, and calcium supplementation. 99mTc sestamibi gammagram showed findings suggestive of parathyroid hyperplasia. Bone histomorphometry showed an image consistent with hyperparathyroidism without findings of osteomalacia, so normocalcemic primary hyperparathyroidism was suspected and a subtotal parathyroidectomy was performed, with the patient developing postoperative hypoparathyroidism. When she arrived at our clinic at age 18 years, she showed calcium- and calcitriol-dependent hypocalcemia, with secondary hyperparathyroidism and low levels of 1,25(OH)2 vitamin D in the absence of a 25-OH vitamin D deficiency, reflecting a defect in 1α-hydroxylation. Molecular testing revealed compound heterozygous variants in CYP27B1 gene. This is the first reported case of an inherited disorder of vitamin D metabolism that was diagnosed and surgically treated as primary hyperparathyroidism.

Validation of an equation for free calcium estimation: accuracy improves after adjustment for phosphate and CO2

PURPOSE

Free calcium is the gold standard for diagnosis of calcium disorders, although calcium assessment is routinely performed by albumin-adjusted calcium. Our objective was to develop a novel-specific correction equation for free calcium employing serum total calcium and other analytes.

METHODS

Retrospective single-center cohort study. A new equation for free calcium assessment was formulated from data of hospitalized patients (n = 3481, measurements = 7157) and tested in a validation cohort (n = 3218, measurements = 6911). All measurements were performed simultaneously from the same blood draw.

RESULTS

Total CO₂ and phosphate, in addition to albumin, were the principal factors associated to calcium misdiagnosis. A novel laboratory-specific prediction equation was developed: free calcium (mmol/L) = 0.541 + (total calcium [mmol/L] *0.441) - (serum albumin [g/L] *0.0067) - (serum phosphate [mmol/L] *0.0425) - (CO₂ [mmol/L] *0.003). This new equation substantially improved adjusted R² to 0.67 (95% CI 0.78-0.82, p < 0.001; Kendall's c-tau: 0.28, p < 0.001). Bland-Altman plots of estimated free calcium and free calcium showed a mean difference of - 0.0006 mmol/L (LOA + 0.126 to - 0.124). In validation cohort, the AUC-ROC curves for hypercalcemia and hypocalcemia diagnosis deploying the new equation were 0.88 (95% CI 0.86-0.89, p < 0.001) and 0.98 (95% CI 0.97-99, p < 0.001), respectively, which were superior to historical formulas for calcium. In univariate models, eGFR was associated with Ca-status misdiagnosis, yet this association disappeared when analysis was adjusted to phosphate and CO₂.

CONCLUSIONS

The novel equation proposed for prediction of free calcium could be useful when free calcium is not available. The conventional formulas misclassify many patients, in particular when phosphate or bicarbonate disturbances are present.

Etomidate in the control of severe Cushing's syndrome by neuroendocrine carcinoma

Etomidate is a very effective drug in severe Cushing's syndrome that is refractory to ketoconazol. Control of the serum cortisol levels in ectopic Cushing's syndrome can be obtained with infusion rates much lower than those used in anesthesia, without respiratory side effects.

The Mexican Acromegaly Registry: Clinical and Biochemical Characteristics at Diagnosis and Therapeutic Outcomes

CONTEXT

Acromegaly is a systemic disorder caused by a GH-secreting pituitary adenoma. As with other rare diseases, acromegaly registries developed in various European countries have provided us with important information.

OBJECTIVE

The objective of the study was to analyze the epidemiological, clinical, biochemical, and therapeutic data from the Mexican Acromegaly Registry (MAR).

SETTING

The setting of the study was a nationwide patient registry.

DESIGN AND METHODOLOGY

The MAR was created in 2009. It gathers data from 24 participating centers belonging to three different institutions using a specifically designed on-line platform. Only patients diagnosed after 1990 were included in the program.

RESULTS

A total of 2057 patients (51% female, mean age at diagnosis 41.1 ± 24.5 y) have been registered for an estimated prevalence of 18 cases per 1 million inhabitants. Hypertension, glucose intolerance, diabetes, and dyslipidemia were present in 27%, 18.4%, 30%, and 24% of the patients, respectively. The IGF-1 level at diagnosis and the concomitant presence of hypertension were significantly associated with the development of diabetes. Transsphenoidal surgery was the primary treatment in 72% of the patients. Pharmacological treatment, mostly with somatostatin analogs, was administered primarily and adjunctively in 26% and 54% of the patients, respectively. Treatment choice varied among the three participating institutions, with the predominance of pharmacological therapy in two of them and of radiation therapy in the third. Therapeutic outcomes were similar to those reported in the European registries.

CONCLUSIONS

The MAR is the largest and first non-European registry of the disease. Our findings highlight important within-country differences in treatment choice due to variations in the availability of resources.

[Osteoporosis]

Calcium intake has a role on the development of peak bone mass, and has a mild impact on the maintenance of bone mass during adulthood and the reduction of bone loss rate in postmenopausal women and the elderly in both genders. Calcium dietary intake should be privileged over supplementation. Dairy products are the main calcium dietary sources. Prospective studies have not clearly demonstrated an effect on the prevention of fractures, because of the practical difficulties of a long follow-up in order to get to solid conclusions; however the physiological rationale is that an adequate calcium intake and 25(OH) vitamin D levels exceeding 20 ng/ml is beneficial for bone health and may decrease to certain extent the risk of fractures.

Radioiodine Treatment in Autoimmune Hyperthyroidism: Analysis of Outcomes in Relation to Dosage

BACKGROUND

Controversy exists regarding the optimal dose of radioiodine ((131)I) therapy in autoimmune hyperthyroidism (i.e., Graves' Disease).

METHODS

In order to evaluate the efficacy and safety of high dose (131)I therapy in autoimmune hyperthyroidism, a retrospective review of patients who received (131)I therapy for Graves' disease from 1980 to 2000 in the Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City was carried out.

RESULTS

The study population consisted of 596 autoimmune hyperthyroid patients with a mean age of 35 years. The mean follow-up period was 10.31 +/- 2.37 years. Remission of hyperthyroidism occurred in 81.9%, persistent hyperthyroidism was recorded in 14.4% and recurrence in 3.7%. (131)I doses of 5-9 mCi (185-333 MBq) and > or =20 mCi (> or =740 MBq) were associated with remission rates of 65.5% and 87.7% respectively. Remission occurred earlier and more often with high doses of (131)I. The high-dose group (20-30 mCi [740-1110 MBq]) had the lowest rate of persistence (9.7, 27.5 and 34.3%, for 20-30 [740-1110 MBq], 10-14 [370-518 MBq] and 5-9 [185-333 MBq] mCi, respectively p <0.05) and hypothyroidism occurred earlier in this group (p = 0.05).

CONCLUSIONS

Remission of autoimmune hyperthyroidism is more likely with doses of 20-30 mCi (740-1110 MBq).

Physiological effects of slow release potassium phosphate for absorptive hypercalciuria: a randomized double-blind trial

PURPOSE

We examined the physiological effects and tolerance of UroPhos-K, a slow release neutral form of potassium phosphate (155 mg. phosphate and 8 mEq. potassium per tablet) in patients with absorptive hypercalciuria.

MATERIALS AND METHODS

A total of 31 patients with absorptive hypercalciuria were studied at baseline and after 3 months of treatment with 4 tablets twice daily of UroPhos-K or placebo (identical in appearance) in a prospective randomized, placebo controlled, double-blind trial during a 4-day inpatient study with a daily constant metabolic diet containing 400 mg. calcium, 100 mEq. sodium and 800 mg. phosphate.

RESULTS

Treatment with UroPhos-K did not cause significant gastrointestinal side effects, increase fasting serum potassium or phosphorus, or reduce hemoglobin or creatinine clearance. It reduced urinary calcium excretion from 277 +/- 72 to 166 +/- 43 mg. per day (p < 0.001), associated with a reduction in serum 1,25-dihydroxyvitamin D concentration from 50 +/- 11 to 42 +/- 9 pg./ml. (p < 0.001). Indexes of intestinal calcium absorption and markers of bone turnover also decreased modestly. None of these changes was seen in the placebo group.

CONCLUSIONS

In patients with absorptive hypercalciuria UroPhos-K seems to correct hypercalciuria by a combination of reduced intestinal absorption, bone resorption and improved renal calcium reabsorption. The drug is well tolerated compared to placebo.

Physiological effects of slow release potassium phosphate for absorptive hypercalciuria: a randomized double-blind trial

PURPOSE

We examined the physiological effects and tolerance of UroPhos-K, a slow release neutral form of potassium phosphate (155 mg. phosphate and 8 mEq. potassium per tablet) in patients with absorptive hypercalciuria.

MATERIALS AND METHODS

A total of 31 patients with absorptive hypercalciuria were studied at baseline and after 3 months of treatment with 4 tablets twice daily of UroPhos-K or placebo (identical in appearance) in a prospective randomized, placebo controlled, double-blind trial during a 4-day inpatient study with a daily constant metabolic diet containing 400 mg. calcium, 100 mEq. sodium and 800 mg. phosphate.

RESULTS

Treatment with UroPhos-K did not cause significant gastrointestinal side effects, increase fasting serum potassium or phosphorus, or reduce hemoglobin or creatinine clearance. It reduced urinary calcium excretion from 277 +/- 72 to 166 +/- 43 mg. per day (p < 0.001), associated with a reduction in serum 1,25-dihydroxyvitamin D concentration from 50 +/- 11 to 42 +/- 9 pg./ml. (p < 0.001). Indexes of intestinal calcium absorption and markers of bone turnover also decreased modestly. None of these changes was seen in the placebo group.

CONCLUSIONS

In patients with absorptive hypercalciuria UroPhos-K seems to correct hypercalciuria by a combination of reduced intestinal absorption, bone resorption and improved renal calcium reabsorption. The drug is well tolerated compared to placebo.

Sustained reduction in urinary calcium during long-term treatment with slow release neutral potassium phosphate in absorptive hypercalciuria

PURPOSE

We tested whether UroPhos-K, a new slow release neutral form of potassium phosphate (155 mg. phosphate, 8 mEq. potassium per tablet) in a dose of 4 tablets twice daily would produce a sustained hypocalciuric response and maintain bone mass in patients with absorptive hypercalciuria, a major cause of nephrolithiasis characterized by excessive intestinal calcium absorption accompanied in some patients by excessive bone loss.

MATERIALS AND METHODS

A total of 25 patients with absorptive hypercalciuria were studied in a 4-year, prospective, open trial with UroPhos-K at yearly intervals during a 4-day inpatient physiological study with a constant metabolic diet containing 400 mg. calcium, 100 mEq. sodium and 800 mg. phosphate daily.

RESULTS

Treatment with UroPhos-K caused a sustained, marked reduction in urinary calcium (264 to 181 mg. daily). Fractional 47calcium absorption decreased modestly (74.0 to 64.6%) commensurate with a reduction in serum 1,25-dihydroxyvitamin D (42 to 34 pg./ml.). Intact parathyroid hormone increased within the normal range (30 to 42 pg./ml.). Bone mineral density was stable at the lumbar spine, femoral neck and distal third of the radius.

CONCLUSIONS

UroPhos-K may provide a long-term alternative for hypercalciuric patients in whom thiazide therapy fails.