Betty Y L Wong's research while affiliated with Sunnybrook Health Sciences Centre and other places

Context Recent studies have reported elevated urinary vitamin D binding protein (uVDBP) concentrations in patients with diabetic kidney disease, although the utility of uVDBP to predict deterioration of kidney function over time has not been examined. Objective Our objective was to assess the association of uVDBP with longitudinal changes in kidney function. Methods Adults at-risk for type 2 diabetes from the Prospective Metabolism and Islet Cell Evaluation (PROMISE) study had 3 assessments over 6 years (n = 727). Urinary albumin-to-creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) were used as measures of kidney function. Measurements of uVDBP were performed with enzyme-linked immunosorbent assay and normalized to urine creatinine (uVDBP:cr). Generalized estimating equations (GEEs) evaluated longitudinal associations of uVDBP and uVDBP:cr with measures of kidney function, adjusting for covariates. Results Renal uVDBP loss increased with ACR severity at baseline. Individuals with normoalbuminuria, microalbuminuria, and macroalbuminuria had median log uVDBP:cr concentrations of 1.62 μg/mmol, 2.63 μg/mmol, and 2.48 μg/mmol, respectively, and ACR positively correlated with uVDBP concentrations (r = 0.37; P < .001). There was no significant association between uVDBP and eGFR at baseline. Adjusted longitudinal GEE models indicated that each SD increase both in baseline and longitudinal uVDBP:cr was significantly associated with higher ACR over 6 years (β = 30.67 and β = 32.91, respectively). Conversely, neither baseline nor longitudinal uVDBP:cr measures showed a significant association with changes in eGFR over time. These results suggest that loss of uVDBP:cr over time may be a useful marker for predicting renal tubular damage in individuals at risk for diabetes.

Background Fluoropyrimidine drugs are widely used in chemotherapy to treat solid tumors. However, severe toxicity has been reported in 10% to 40% of patients. The DPYD gene encodes the rate-limiting enzyme dihydropyrimidine dehydrogenase responsible for fluoropyrimidine catabolism. The DPYD variants resulting in decreased or no enzyme activity are associated with increased risk of fluoropyrimidine toxicity. This study aims to develop a pharmacogenetic test for screening DPYD variants to guide fluoropyrimidine therapy. Methods A multiplex allele-specific polymerase chain reaction (AS-PCR) assay, followed by capillary electrophoresis, was developed to detect 5 common DPYD variants (c.557A > G, c.1129–5923C > G, c.1679T > G, c.1905 + 1G > A, and c.2846A > T). Deidentified population samples were used for screening positive controls and optimizing assay conditions. Proficiency testing samples with known genotypes were analyzed for test validation. All variants detected were confirmed by Sanger sequencing. Results From the deidentified population samples, 5 samples were heterozygous for c.557A > G, 2 samples were heterozygous for c.1129–5923C > G (HapB3), and 1 sample was heterozygous for c.2846A > T. The 20 proficiency samples matched with their assigned genotypes, including 13 wild-type samples, 3 samples heterozygous for c.1679T > G, 2 samples heterozygous for c.1905 + 1G > A, and 2 samples heterozygous for c.2846A > T. One of the 3 patient samples was heterozygous for c.1129–5923C > G (HapB3). All the variants detected by the multiplex AS-PCR assay were concordant with Sanger sequencing results. Conclusions A robust multiplex AS-PCR assay was developed to rapidly detect 5 variants in the DPYD gene. It can be used for screening DPYD variants to identify patients with increased risk of toxicity when prescribed fluoropyrimidine therapy.

Objectives: In a large cohort of healthy infants and toddlers 6 to 36 months of age (n=776), we have been exploring the potential role of genetic variation in predisposition to vitamin D insufficiency. The genes encoding the key cytochrome P450 hydroxylases (CYP2R1, CYP24A1, and CYP27B1) harbour recurrent mutations of uncertain effect. This study was undertaken to look for biochemically relevant associations of these variants with inter-individual differences in vitamin D metabolism in an at-risk pediatric population. Methods: Genotyping for CYP2R1-CT (c.-1127C>T, rs10741657), CYP24A1-AG (c.-686A>G, rs111622401), and CYP27B1-CA (c.-1261C>A, rs10877012) mutations were performed using SNaPshot assay, followed by Sanger sequencing confirmation. Vitamin D metabolites and vitamin D binding protein (DBP) were measured by established methods. Results: In a multivariate regression model, with corrections for co-variates, subjects with the homozygous CYP2R1-TT variant had significantly higher concentrations of 25(OH)D, free 25(OH)D, and 24,25(OH)2D levels. In subjects with the CYP24A1-AG mutation, concentrations of 25(OH)D were significantly higher. Conclusions: The CYP2R1-TT and CYP24A1-AG variants have measurable effects on the vitamin D pathway. It seems unlikely that they will be clinically relevant in isolation, but they may be members of the large pool of infrequent mutations contributing to different risks for the vitamin D deficiency phenotype.

Objective: Our aim was to analyze variants of the gene glial cells missing-2 ( GCM2 ), encoding a parathyroid cell-specific transcription factor, in familial hypoparathyroidism, and in Familial Isolated Hyperparathyroidism (FIHP) without and with a parathyroid carcinoma. Design: We characterized two families with hypoparathyroidism, and nineteen with FIHP in which we examined the mechanism of action of GCM2 variants. Methods: Leukocyte DNA of hypoparathyroid individuals was Sanger sequenced for CASR , PTH , GNA11 and GCM2 mutations. DNA of hyperparathyroid individuals underwent MEN1 , CDKN1B , CDC73 , CASR , RET and GCM2 sequencing. The actions of identified GCM2 variants were evaluated by in vitro functional analyses. Results: A novel homozygous p.R67C GCM2 mutation which failed to stimulate transcriptional activity in a luciferase assay was identified in affected members of two hypoparathyroid families. Oligonucleotide pulldown assay and in silico structural modeling indicated that this mutant had lost the ability to bind the consensus GCM recognition sequence of DNA. Two novel (p.I383M and p.T386S) and one previously reported (p.Y394S), heterozygous GCM2 variants that lie within a C-terminal conserved inhibitory domain (CCID) were identified in affected individuals of three of the hyperparathyroid families. One family member, heterozygous for p.I138M, had parathyroid carcinoma (PC), and a heterozygous p.V382M variant was found in another patient affected by sporadic PC. These variants exerted significantly enhanced in vitro transcriptional activity, including increased stimulation of the PTH promoter. Conclusions: We provide evidence that 2 novel GCM2 R67C inactivating mutations with inability to bind DNA are causative of hypoparathyroidism. Additionally, we provide evidence that two novel GCM2 variants increased transactivation of the PTH promoter in vitro and are associated with FIHP. Furthermore, our studies suggest that activating GCM2 variants may contribute to facilitating more aggressive parathyroid disease.

The gene (GC) for the vitamin D binding protein (DBP) shows significant genetic variation. Two missense variants, p.D432E and p.T436K, are common polymorphisms and both may influence vitamin D metabolism. However, less common variants, identified biochemically, have been reported previously. This study aimed to identify the underlying mutations by molecular screening and to characterize the mutant proteins by mass spectrometry. Denaturing high performance liquid chromatography (DHPLC) was used for screening genetic variants in GC exons and exon/intron boundaries of genomic DNA samples. Sanger sequencing identified the specific mutations. An immuno-capture coupled mass spectrometry method was used to characterize protein variants in serum samples. Initial molecular screening identified 10 samples (out of 761) containing an alanine deletion at codon 246 in exon 7 (p.A246del, c.737_739delCTG), and 1 sample (out of 97) containing a cysteine to phenylalanine substitution at codon 311 in exon 8 (p.C311F, c.932G > T). The mutant allele proteins and posttranslational modified products were distinguishable from the wild-type proteins by mass spectrum profiling. Loss of a disulfide bond due to loss of cysteine-311 was accompanied by the appearance of a novel mixed disulfide species, consistent with S-cysteinylation of the remaining unpaired cysteine-299 in the mutant protein. We confirm earlier biochemical studies indicating that there are additional deleterious GC mutations, some of which may be low-frequency variants. The major findings of this study indicate that additional mutant proteins are secreted and can be identified in the circulation. By combining molecular screening and mass spectrometric methods, mutant DBP species can be identified and characterized.

The 22q11.2 deletion syndrome (DS) is a common multiple anomaly syndrome in which typical features include congenital heart defects, facial dysmorphism and palatal anomalies. Hypocalcemia due to hypoparathyroidism is a common endocrine manifestation resulting from variable parathyroid hypoplasia, but hypercalcemia has not previously been reported in 22q11.2 DS. Our patient is a 16-year-old adolescent male with dysmorphic facial features, delayed motor and speech development. At 2 years of age, 22q11.2 DS was confirmed by FISH. In contrast to hypoparathyroidism that is usually seen in 22q11.2 DS, this patient had early childhood-onset hypercalcemia with inappropriately high PTH levels and hypocalciuria. Genomic DNA was obtained from the proband and screened for calcium-sensing receptor (CASR) mutations with negative results. No parathyroid tissue could be localized by imaging or surgical exploration. Due to symptomatic hypercalcemia, the patient was treated with a calcimimetic (cinacalcet). During the treatment, plasma calcium normalized with mild symptoms of hypocalcemia. After discontinuation of cinacalcet, calcium returned to high pretreatment levels. Further DNA analysis of adaptor protein-2 σ subunit (AP2S1) showed a heterozygous missense mutation c.44 G>T resulting in a p.R15L substitution; the mutation was absent in the healthy parents and two siblings. Hypercalcemia in our patient with 22q11.2 DS could be explained by the de novo mutation in AP2S1. Identification of a genetic cause for hypercalcemia is helpful in guiding management and avoiding unnecessary treatment.

Background: Observational studies have shown that vitamin D binding protein (DBP) levels, a key determinant of 25-hydroxy-vitamin D (25OHD) levels, and 25OHD levels themselves both associate with risk of disease. If 25OHD levels have a causal influence on disease, and DBP lies in this causal pathway, then DBP levels should likewise be causally associated with disease. We undertook a Mendelian randomization study to determine whether DBP levels have causal effects on common calcemic and cardiometabolic disease. Methods and findings: We measured DBP and 25OHD levels in 2,254 individuals, followed for up to 10 y, in the Canadian Multicentre Osteoporosis Study (CaMos). Using the single nucleotide polymorphism rs2282679 as an instrumental variable, we applied Mendelian randomization methods to determine the causal effect of DBP on calcemic (osteoporosis and hyperparathyroidism) and cardiometabolic diseases (hypertension, type 2 diabetes, coronary artery disease, and stroke) and related traits, first in CaMos and then in large-scale genome-wide association study consortia. The effect allele was associated with an age- and sex-adjusted decrease in DBP level of 27.4 mg/l (95% CI 24.7, 30.0; n = 2,254). DBP had a strong observational and causal association with 25OHD levels (p = 3.2 × 10(-19)). While DBP levels were observationally associated with calcium and body mass index (BMI), these associations were not supported by causal analyses. Despite well-powered sample sizes from consortia, there were no associations of rs2282679 with any other traits and diseases: fasting glucose (0.00 mmol/l [95% CI -0.01, 0.01]; p = 1.00; n = 46,186); fasting insulin (0.01 pmol/l [95% CI -0.00, 0.01,]; p = 0.22; n = 46,186); BMI (0.00 kg/m(2) [95% CI -0.01, 0.01]; p = 0.80; n = 127,587); bone mineral density (0.01 g/cm(2) [95% CI -0.01, 0.03]; p = 0.36; n = 32,961); mean arterial pressure (-0.06 mm Hg [95% CI -0.19, 0.07]); p = 0.36; n = 28,775); ischemic stroke (odds ratio [OR] = 1.00 [95% CI 0.97, 1.04]; p = 0.92; n = 12,389/62,004 cases/controls); coronary artery disease (OR = 1.02 [95% CI 0.99, 1.05]; p = 0.31; n = 22,233/64,762); or type 2 diabetes (OR = 1.01 [95% CI 0.97, 1.05]; p = 0.76; n = 9,580/53,810). Conclusions: DBP has no demonstrable causal effect on any of the diseases or traits investigated here, except 25OHD levels. It remains to be determined whether 25OHD has a causal effect on these outcomes independent of DBP. Please see later in the article for the Editors' Summary.

Background NSHPT is a life threatening disorder caused by homozygous inactivating calcium-sensing receptor (CASR) mutations. In some cases, the CaSR allosteric activator, cinacalcet, may reduce serum PTH and calcium levels, but surgery is the treatment of choice. Objective To describe a case of NSHPT unresponsive to cinacalcet. Patient and Results A 23-day-old girl was admitted with hypercalcaemia, hypotonia, bell-shaped chest and respiratory distress. The parents were first-degree cousins once removed. Serum Ca was 4.75 mmol/l (N: 2.10-2.62), P: 0.83 mmol/l (1.55-2.64), PTH: 1096 pg/ml (9–52) and urinary Ca/Cr ratio: 0.5 mg/mg. First, calcitonin was given (10 IU/kg x 4/day) and then two days later, pamidronate (0.5 mg/kg) for 2 days. Doses of cinacalcet were given daily from day 28 of life starting at 30 mg/m2 and increasing to 90 mg/m2 on day 43. On day 33, 6 days after pamidronate, serum Ca levels had fallen to 2.5 mmol/l, but thereafter rose to 5 mmol/l despite the cinacalcet. Total parathyroidectomy was performed at day 45. Hungry bone disease after surgery required daily Ca replacement and calcitriol for 18 days. At 3 months, the girl was mildly hypercalcemic, with no supplementation, and at 6 months, she developed hypocalcemia and has since been maintained on Ca and calcitriol. By CASR mutation analysis, the infant was homozygous and both parents heterozygous for a deletion-frameshift mutation. Conclusion The predicted nonfunctional CaSR is consistent with lack of response to cinacalcet, but total parathyroidectomy was successful. An empiric trial of the drug and/or prompt mutation testing should help minimize the period of unnecessary pharmacotherapy.

Context: Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant disorder with three known subtypes: FHH1, FHH2, and FHH3. About 65% of FHH cases are FHH1, caused by inactivating mutations of the calcium-sensing receptor (CASR) gene. FHH3 was recently found to be caused by codon Arg15 (p.R15) mutations in the adaptor-related protein complex 2, σ-2 subunit that interacts with the CaSR and is encoded by the AP2S1 gene. Objective: The objective of the study was to assess the prevalence of AP2S1 mutations, and describe the phenotype of FHH3, in an independent cohort of FHH subjects lacking CASR mutations. Patients and methods: Thirty-nine patients presenting with some combination of hypercalcemia, hypermagnesemia, nonsuppressed serum PTH levels, and reduced urinary calcium excretion were studied. Exon 2 of the AP2S1 gene was PCR amplified from patient genomic DNA and Sanger sequenced. The presence of p.R15 mutations was confirmed by restriction enzyme analysis. Results: Five of the 39 subjects had AP2S1 p.R15 mutations, a frequency of 13%. The three recurrent mutations reported previously were all found in our cohort (p.R15C in two, p.R15L in two, and p.R15H in one subject). The FHH3 phenotype did not differ materially from that of FHH1 due to CASR mutations. Conclusions: The results affirm that a significant number of patients suspected of having FHH but proven negative for CASR mutation have AP2S1 p.R15 mutations. Screening for AP2S1 p.R15 mutations in such cases should be considered, given the clinical benefits (avoiding unnecessary parathyroidectomy) that have already been demonstrated for CASR screening in FHH1.