Understanding Musculoskeletal Disorders Through Next-Generation Sequencing

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An insight into musculoskeletal disorders through advancements in next-generation sequencing (NGS) promises to maximize benefits and improve outcomes through improved genetic diagnosis.

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The primary use of whole exome sequencing (WES) for musculoskeletal disorders is to identify functionally relevant variants.

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The current evidence has shown the superiority of NGS over conventional genotyping for identifying novel and rare genetic variants in patients with musculoskeletal disorders, due to its high throughput and low cost.

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Genes identified in patients with scoliosis, osteoporosis, osteoarthritis, and osteogenesis imperfecta using NGS technologies are listed for further reference.

Expression of osteogenic molecules in the caudate nucleus and gray matter and their potential relevance for Basal Ganglia calcification in hypoparathyroidism

BACKGROUND

Basal ganglia calcification (BGC) is an interesting example of ectopic calcification in patients with hypoparathyroidism. Its pathogenesis and reasons for predilection of calcification at basal ganglia are not clear.

OBJECTIVE

To assess the expression of osteogenesis-related molecules in the caudate nucleus and surface gray matter (an area spared from calcification) and discuss potential relevance of the results in context of BGC in idiopathic hypoparathyroidism.

METHODS

Caudate nucleus and gray matter were obtained from 14 autopsies performed in accidental deaths. The mRNA expression of bone transcription factors (RUNX2/osterix), bone morphogenetic proteins (BMPs) 2 and 4, osteonectin, osteopontin, osteocalcin, vitamin D receptor, calcium sensing-receptor, Na phosphate transporters (PiTs) 1 and 2, N-methyl-D-aspartate receptor 2B (NMDAR2B), carbonic anhydrase II (CA-II), PTH1 receptor (PTH1R), PTH2R, and PTHrP were assessed by RT-PCR. Western blot, spot densitometry, and immunohistochemistry were performed to assess protein expression of molecules showing differences in mRNA expression between caudate and gray tissues.

RESULTS

The mean mRNA expression of PiT1 (11.0 ± 10.39 vs 32.9 ± 20.98, P = .003) and PTH2R (1.6 ± 1.47 vs 13.7 ± 6.11, P = .001) were significantly lower in the caudate nucleus than the gray matter. The expression of osteonectin, osteopontin, and CA-II were significantly higher in the caudate nucleus than the gray matter (P = .01, .001, and .04, respectively). The mRNA expression of other molecules was comparable in the 2 tissues. The protein expression of both CA-II and osteonectin was 24% higher and PiT1 17% lower in caudate than the gray matter. The differences in the PTH2R and osteopontin protein expression were not appreciable.

CONCLUSIONS

The presence of several osteogenic molecules in caudate nucleus indicates that BGC would probably be the outcome of an active process. The differences in expression of these molecules in caudate over gray matter could favor BGC at this site in the unique biochemical milieu of hypoparathyroid state.

Calcium-sensing receptor autoantibodies and idiopathic hypoparathyroidism

CONTEXT

Data on calcium-sensing receptor autoantibodies (CaSRAbs) in hypoparathyroidism are variable.

OBJECTIVE

We assessed the prevalence and significance of CaSRAbs in idiopathic hypoparathyroidism.

DESIGN

This was a case-control study.

SUBJECTS

One hundred forty-seven patients with idiopathic hypoparathyroidism treated during 1998-2011 in a tertiary care setting and 348 controls [healthy, n = 199; type 1 diabetes mellitus (T1DM), n = 99; and chronic lymphocytic thyroiditis (CLT), n = 50] participated in the study.

METHODS

CaSRAb assays included Western blot with CaSR protein expressed in Escherichia coli or human embryonic kidney (HEK)-293 cells, immunoprecipitation (IP) using in vitro-transcribed/translated protein, and indirect immunofluorescence on HEK293-CaSR. Functional significance was assessed by ERK1/2 phosphorylation. PTH and CaSR genes were sequenced for mutations.

RESULTS

E coli-Western blot assay revealed 16.3% CaSRAb positivity in idiopathic hypoparathyroidism, which was comparable with healthy subjects and CLT but significantly less than the T1DM controls. The prevalence of CaSRAbs on HEK293-Western blot (24.5%) against 150 kDa and/or 168 kDa protein in hypoparathyroidism was significantly higher than the healthy subjects, T1DM, and CLT. IP assay showed CaSRAbs in 12.9% of the hypoparathyroid patients but not in controls. The sensitivity and specificity of CaSRAbs in E coli and HEK-293-CaSR Western blot and IP assays were 16.3% and 83.1%, 24.5% and 88.9%, and 12.9% and 100%, respectively, and 42.1% of the cases detected were common in the IP assay and HEK293-Western blot. Duration of illness and coexistent autoimmunity were similar in patients with and without CaSRAbs. The CaSRAb-positive sera showed no immunofluorescence and phosphorylated ERK1/2 activity. The CaSR gene sequence was normal in all patients. One of the patients showed a novel p.Met1_Asp6del mutation in the signal peptide region of the PTH gene.

CONCLUSION

IP performed the best in detecting CaSRAbs in 12.9% of hypoparathyroid patients. Although CaSRAbs were functionally inert, its clinical relevance remains due to 100% specificity. Limited prevalence of CaSRAb suggests heterogeneity in the etiology of idiopathic hypoparathyroidism or the presence of CaSR epitopes other than those measured in the current study.

Prevalence and significance of NALP5 autoantibodies in patients with idiopathic hypoparathyroidism

CONTEXT

Role of parathyroid autoimmunity in idiopathic hypoparathyroidism (IH) is not clear. Recently, parathyroid-specific NACHT leucine-rich-repeat protein 5 (NALP5) autoantibodies (Ab) have been reported in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome.

OBJECTIVE

Our objective was to assess prevalence and significance of NALP5 Ab in patients with IH.

DESIGN AND SETTING

This was a case-control study at a tertiary care hospital.

SUBJECTS

Subjects included 145 patients with IH recruited from 1998-2011 and 152 healthy controls.

METHODS

Immunoprecipitation (IP) and Western blot (WB) assays were performed using ³⁵S-labeled NALP5 protein produced by in vitro transcription-translation and recombinant NALP5 protein in Escherichia coli, respectively. AIRE gene sequencing was performed in NALP5 Ab-positive patients.

RESULTS

One of 145 patients (0.69%) and none of the 152 controls had NALP5 Ab on IP assay. Nine of 147 patients (6.12%) and four of 152 controls (2.63%) had NALP5 Ab on WB. One patient with NALP5 Ab on IP (36.6 sd score), also positive on WB, had a frameshift p.Ala386Serfs*38 AIRE gene mutation and adrenocortical Ab. Eight subjects with NALP5 Ab detected on WB had normal AIRE gene sequence.

CONCLUSIONS

IP is currently the best assay to detect clinically relevant NALP5 Ab. Presence of NALP5 Ab in only one patient with IH who also had AIRE gene mutation suggests that these Ab are exceptionally rare in IH (0.69%) and, when present, occur in context of the autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome.

Prevalence of clinical remission in patients with sporadic idiopathic hypoparathyroidism

BACKGROUND

Remission of disease activity is a characteristic feature of autoimmune endocrine disorders such as Graves' disease, Addison's disease and occasionally in patients with premature ovarian failure. Autoimmunity is also implicated in sporadic idiopathic hypoparathyroidism (SIH) with clinical remission of disease reported in three cases.

OBJECTIVE

To assess the rate of remission in patients with sporadic idiopathic hypoparathyroidism and review the cases reported so far.

SUBJECTS AND METHODS

Subjects included 53 patients (M:F, 24:29) with SIH who had been symptomatic for at least 1 year (range 1-31 years). They were treated with calcium and 1-alpha-(OH)D(3)/cholecalciferol therapy and had a mean duration of follow up of 5.0 +/- 3.2 years. Treatment was withdrawn in two stages in the patients who maintained normal levels of serum total calcium during the preceding year of treatment. In stage-1, the dose of therapy was reduced to half and subsequently all treatment was stopped (stage 2) in those patients who maintained normal serum total calcium levels on the reduced dose. Remission of SIH was defined as maintenance of normal serum total (>or=2.12 mmol/l) and ionized calcium, inorganic phosphorus and serum intact parathyroid hormone (iPTH) for at least 3 months after withdrawal of calcium and 1-alpha-(OH)D(3)/cholecalciferol therapy. Calcium sensing receptor autoantibodies (CaSRAb) were determined by Western blot.

RESULTS

Two of the 53 patients (3.8%) with SIH stayed in remission for 1 year after complete withdrawal of therapy. CaSRAb was absent in both the cases. The clinical features, age at onset and duration of hypocalcaemic symptoms in cases with remission were comparable to those who did no show remission.

CONCLUSION

Sporadic idiopathic hypoparathyroidism is not irreversible as is widely believed and spontaneous remission of disease may occur in 3.8% of patients.

Presence and significance of a R110W mutation in the DNA-binding domain of GCM2 gene in patients with isolated hypoparathyroidism and their family members

OBJECTIVE

Glial cells missing 2 (GCM2) gene encodes a parathyroid-specific transcription factor. We assessed GCM2 gene sequence in patients with isolated hypoparathyroidism (IH).

DESIGN

Case-control study.

METHODS

Complete DNA sequencing of the GCM2 gene including its exons, promoter, and 5' and 3' UTRs was performed in 24/101 patients with IH. PCR-restriction fragment length polymorphism was used to detect a novel R110W mutation in all 101 IH patients and 655 healthy controls. Significance of the mutation was assessed by electrophoretic mobility shift assay (EMSA) and nuclear localization on transfection.

RESULTS

A heterozygous R110W mutation was present in DNA-binding domain in 11/101 patients (10.9%) and absent in 655 controls (P<10(-7)). Four of 13 nonaffected first-degree relatives for five of these index cases had R110W mutation. Four heterozygous single nucleotide polymorphisms were found in the 5' region. One of the 11 patients with R110W also had T370M change in compound heterozygous form. Mutant R110W and T370M GCM2 proteins showed decreased binding with GCM recognition elements on EMSA indicating loss of function. Both wild-type and R110W mutant GCM2 proteins showed nuclear localization.

CONCLUSIONS

The present study indicates a significant association of R110W variant with IH. Absence of effect of heterozygous R110W mutation on DNA binding and presence of the same mutation in asymptomatic family members indicate that additional genetic (akin to T370M change) or nongenetic factors might contribute to the expression of diseases in IH. Alternatively, it is possible that association of R110W with IH could be due to linkage disequilibrium with the unidentified relevant genes in IH.

Presence of a deletion mutation (c.716delA) in the ligand binding domain of the vitamin D receptor in an Indian patient with vitamin D-dependent rickets type II

Vitamin D-dependent rickets type II (VDDR-type II) is a rare disorder caused by mutations in the vitamin D receptor (VDR) gene. Here, we describe a patient with VDDR-type II with severe alopecia and rickets. She had hypocalcemia, hypophosphatemia, secondary hyperparathyroidism, and elevated serum alkaline phosphatase and 1,25-dihydroxyvitamin D(3). Sequence analysis of the lymphocyte VDR cDNA revealed deletion mutation c.716delA. Sequence analysis of her genomic DNA fragment amplified from exon 6 of the VDR gene incorporating this mutation confirmed the presence of the mutation in homozygous form. This frameshift mutation in the ligand binding domain (LBD) resulted in premature termination (p.Lys240Argfs) of the VDR protein. The mutant protein contained 246 amino acids, with 239 normal amino acids at the N terminus, followed by seven changed amino acids resulting in complete loss of its LBD. The mutant VDR protein showed evidence of 50% reduced binding with VDR response elements on electrophoretic mobility assay in comparison to the wild-type VDR protein. She was treated with high-dose calcium infusion and oral phosphate. After 18 months of treatment, she gained 6 cm of height, serum calcium and phosphorus improved, alkaline phosphatase levels decreased, and intact PTH normalized. Radiologically, there were signs of healing of rickets. Her parents and one of her siblings had the same c.716delA mutation in heterozygous form. Despite the complete absence of LBD, the rickets showed signs of healing with intravenous calcium.

Predisposition to vitamin D deficiency osteomalacia and rickets in females is linked to their 25(OH)D and calcium intake rather than vitamin D receptor gene polymorphism

BACKGROUND

Osteomalacia (OSM) and rickets are widely prevalent in developing countries especially in females. The factors associated with such predisposition are not known.

OBJECTIVES

To identify nutritional, endocrine and genetic factors related to calcium and vitamin D metabolism that are associated with OSM/rickets in females.

SUBJECTS AND METHODS

We studied 98 patients with OSM or rickets and their relatives including male and female sibs and parents (n = 221) for the presence of biochemical OSM {low serum 25-hydroxyvitamin D [25(OH)D], raised intact PTH (iPTH) and raised alkaline phosphatase} and associated nutritional and genetic factors. Polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) was used for genotyping vitamin D receptor (VDR) (BsmI and FokI) and PTH gene (BstBI and DraII) single nucleotide polymorphisms (SNPs) in 74 families. The differences in the factors associated with calcium and vitamin D among the different groups were analysed by analysis of variance (ANOVA). Logistic regression analysis and the transmission disequilibrium test (TDT) were carried out to assess association between nutritional and genetic factors, and the disease, respectively.

RESULTS

Most of the patients were female (91.8%). The mean serum 25(OH)D level of the female patients was comparable to that of the female sibs (14.4 +/- 5.7 vs. 18.3 +/- 9.7 nmol/l). The frequency of biochemical OSM was fivefold higher in female than in male sibs (24.4%vs. 4.9%). Female sibs also had significantly lower 25(OH)D, dietary calcium intake and sunshine exposure than male sibs. The frequency of biochemical OSM was comparable between mothers and fathers. The odds of biochemical OSM in the family members was reduced by 11% per 15-min daily sunshine exposure [odds ratio (OR) = 0.89, 95% confidence interval (CI) = 0.81-0.98, P = 0.02] and decreased by 20% per 100 mg dietary calcium intake (OR = 0.80, 95% CI = 0.67-0.96, P = 0.02). VDR/PTH gene SNPs showed no association with OSM/rickets on TDT analysis.

CONCLUSION

Among the immediate family members of patients with OSM/rickets, female sibs have features of biochemical OSM in up to 24.4%. Female sibs, unlike male sibs, share with patients features of markedly low serum 25(OH)D levels, poor dietary calcium intake and poor exposure to sunshine. Genetic factors such as VDR and PTH gene SNPs were not associated with OSM/rickets.

Presence of spondyloarthropathy and its clinical profile in patients with hypoparathyroidism

BACKGROUND

Though spondyloarthropathy has been described in patients with sporadic idiopathic hypoparathyroidism (SIH), the clinical profile is not known.

OBJECTIVES

To describe the clinical profile including radiological features of spondyloarthropathy and prevalence of HLA-B27 allele in patients with hypoparathyroidism, and to identify any differences from ankylosing spondylitis.

SUBJECTS AND METHODS

Clinical characteristics and radiographs of pelvis and spine were assessed in 40 consecutive patients with SIH. Radiographs were assessed by radiologist (RS) and rheumatologist (RG) for the features of spondyloarthropathy including sacroiliitis, syndesmophytes and hip joint calcification, and so on. HLA-B27 genotyping was carried out in patients with SIH, and 195 healthy controls using duplex PCR. Fourteen control radiographs were from age-matched normal individuals.

RESULTS

Three patients with SIH had clinically overt spondyloarthropathy which closely resembled ankylosing spondylitis. Fourteen (eight females and six males) of the 40 patients with SIH showed radiological changes including syndesmophytes in lower dorsal or dorso-lumbar spine (n = 6), sacroiliitis and new bone formation at the acetabular rim of the hip joint (n = 10). Though all six patients demonstrating syndesmophytes had new bone formation at hip, sacroiliitis was seen in only three of them. None of the 14 controls had syndesmophytes, sacroiliitis or hip joint calcification. The mean (SD) duration of illness (15.4 +/- 8.7 vs. 6.5 +/- 5.9 years, P < 0.01), BMI (24.1 +/- 5.2 vs. 20.8 +/- 3.7 kg/m(2), P = 0.04) and frequency of basal ganglia calcification was higher (100%vs. 57.7%, P < 0.01) in patients who showed changes of spondyloarthropathy in comparison to those without these changes. On multiple logistic regression analysis, only duration of hypoparathyroid illness was associated with spondyloarthropathy with an odds ratio of 1.17 (95% CI = 1.05-1.30, P < 0.01) per year increase in the duration. The mean age, serum total calcium, inorganic phosphorus and serum intact PTH (iPTH) levels were not significantly different between SIH patients with and without spondyloarthropathy. The frequency of HLA-B27 allele was comparable between SIH and the control groups.

CONCLUSIONS

Thus, spondyloarthropathy is a distinct clinical entity in patients with SIH. Its salient clinical features include presence of syndesmophytes at the thoracic or thoraco-lumbar spine, mild sacroiliitis, calcification at the acetabular margin of hip, preserved bone density, equal distribution in both sexes and lack of HLA-B27 association. Presence of spondyloarthropathy, like basal ganglia calcification, is associated with longer duration of hypoparathyroidism. It is important to differentiate hypoparathyroid-related spondyloarthropathy from ankylosing spondylitis because the management for the two disorders is different.

Prevalence of thyroid autoimmunity in sporadic idiopathic hypoparathyroidism in comparison to type 1 diabetes and premature ovarian failure

CONTEXT

Thyroid autoimmunity is the most common coexistent endocrinopathy in type 1 diabetes (T1D), Addison's disease, and premature ovarian failure (POF). Although the role of autoimmunity is being investigated in patients with sporadic idiopathic hypoparathyroidism (SIH), there is little information on coexistent thyroid autoimmunity.

OBJECTIVE

Our objective was to assess the prevalence of thyroid peroxidase autoantibodies (TPOAb) and thyroid dysfunction in patients with SIH and its comparison with that in T1D, POF, and Hashimoto's thyroiditis (HT) and age- and sex-matched healthy controls (for SIH).

DESIGN AND SETTING

We conducted a case control study in a tertiary care setting.

PATIENTS AND METHODS

Subjects were consecutive patients with SIH (n = 87), T1D (n = 100), POF (n = 58), and HT (n = 47) and healthy controls (100 females and 64 males). Serum free T3, free T4, TSH, and TPOAb (normal < or = 34 IU/ml) were measured by electrochemiluminescence assay. Subjects with 1) serum TSH at least 5 microU/ml along with TPOAb more than 34 IU/ml; 2) TSH at least 10 microU/ml but normal TPOAb titers; or 3) Graves' disease were considered to have thyroid dysfunction.

RESULTS

TPOAb positivity (> 34 IU/ml) in females was 14.6% in SIH, 24.1% in POF, and 42.1% in T1D compared with 76.6% in HT and 9% in healthy controls. The frequencies of TPOAb positivity and thyroid dysfunction in patients with SIH were comparable to those in control and POF groups, but significantly less than in T1D and HT groups.

CONCLUSION

The frequencies of TPOAb and thyroid dysfunction were not significantly higher in patients with SIH than in healthy controls, unlike in patients with T1D and POF.

Protein tyrosine phosphatase non-receptor type 22 (PTPN22) gene R620W variant and sporadic idiopathic hypoparathyroidism in Asian Indians

Recently, a gain of function variant C1858T of the lymphoid-specific protein tyrosine phosphatase non-receptor (LYP, PTPN22) gene has been reported to be associated with several autoimmune disorders including Graves' disease, type 1 diabetes, rheumatoid arthritis and vitiligo. The present study was carried out in 80 patients with sporadic idiopathic hypoparathyroidism (SIH) [43 males and 37 females, mean +/- SD age and duration of symptoms 32.5 +/- 14.1 years and 6.7 +/- 7.2 years (range 1 day to 35 years), respectively] and 193 healthy controls (male : female ratio 91:102, mean +/- SD age, 43.1 +/- 11.6 years) to assess association of 1858T allele with the disease. Polymerase chain reaction-restriction fragment length polymorphism analysis was performed to genotype C1858T variant. The frequency of occurrence of 1858T allele was 4/160 (2.5%) in SIH and 5/386 (1.3%) in the control alleles (odds ratio 1.95, 95% CI 0.51-7.37). Thus, the present study reveals that 1858T allele is rare (1.3%) in Asian Indians. The trend of higher prevalence of 1858T allele in patients with SIH needs to be studied further in other population with higher rate of the allele to support the autoimmune basis of the disease.

Absence of pathogenic calcium sensing receptor mutations in sporadic idiopathic hypoparathyroidism

BACKGROUND

Sporadic idiopathic hypoparathyroidism (SIH) is the most common cause of hypoparathyroidism. While calcium sensing receptor (CaSR) autoantibodies are observed in 49% of cases, aetiopathogenetic mechanisms in others are under investigation. Mutations in the PTH gene including its 3' untranslated region, autoimmune regulator gene and lead CTLA-4 gene single nucleotide polymorphism (SNPs) are not associated with the disease. There are reports of de novo activating mutations of the CaSR gene in a few patients with SIH.

OBJECTIVE

To assess the frequency of CaSR mutations in patients with SIH.

SUBJECTS AND METHODS

DNA sequencing of all six translating exons and nine of 12 intron/exon boundaries of the CaSR gene was performed by Sangers dideoxy chain termination method using an automated sequencer in 39 patients with SIH. Spot urinary calcium/creatinine ratio in the fasting state and ultrasonography of the abdomen was performed to assess hypercalciuria and nephrolithiasis. The PCR-RFLP analysis was performed using Hin1II restriction endonuclease in 32 additional patients with SIH and 90 healthy controls to further assess the prevalence of a novel missense SNP observed in the DNA sequencing.

RESULTS

Nucleotide sequence analysis revealed the presence of a wild type CaSR gene in all subjects, except in one patient who showed a missense mutation (Val621Met) due to substitution of base G-->A in the heterozygous state at position 79877 in exon 7 (codon 621) coding for the first transmembrane loop of the CaSR. The V621M polymorphism was confirmed by PCR-RFLP and was due to a maternal allele. However, the mother and brother of this patient with the same SNP were asymptomatic and had normal serum chemistry indicating the functionally inert nature of the polymorphism. None of the additional 32 patients with SIH and 90 controls showed V621M SNP. The urinary calcium/creatinine ratio and ultrasonography were normal in all patients with SIH.

CONCLUSION

De novo activating mutation of the CaSR gene typical of familial hypoparathyroidism is not common among patients with SIH in India.

Polymorphisms at +49A/G and CT60 sites in the 3' UTR of the CTLA-4 gene and APECED-related AIRE gene mutations analysis in sporadic idiopathic hypoparathyroidism

Autoimmune diseases such as Graves' disease and type 1 diabetes have been linked with +49A/G and CT60 single nucleotide polymorphisms (SNPs) in the 3' UTR of the cytotoxic T-lymphocyte antigen-4 (CTLA-4) gene. Both these SNPs are functionally relevant and linked with T-lymphocyte activation. Hypoparathyroidism is seen in 70% of patients with autoimmune polyendocrinopathy candidiasis ectodermal dystrophy syndrome (APECED). Although calcium sensing receptor autoantibodies (CaSRAb) and generalized activation of T lymphocytes are reported among patients with sporadic idiopathic hypoparathyroidism (SIH), CTLA-4 gene SNPs and APECED-related autoimmune regulator (AIRE) gene mutations have not been assessed in them. We studied lead CTLA-4 gene SNPs and APECED-related AIRE gene mutations in 73 patients with SIH and 114 healthy subjects. The CTLA-4 gene SNPs +49A/G in exon 1, CT60A/G in 3' UTR and -318C/T in the promoter region were genotyped by polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) using BstEII, NcoI and MseI endonucleases, respectively. The APECED-related AIRE gene mutations, which is R257X (Finn-major) in exon 6, 4-bp insertion and 13-bp deletion in exon 8, and Iranian Jews population 'Y85C' mutation in exon 2, were studied by PCR-RFLP (Taq-I), PCR and nucleotide sequencing, respectively. CaSRAb were studied by immunoblotting. The frequencies of CTLA-4 A/A(49), A/G(49) and G/G(49) genotypes in the patients (47.9%, 38.4% and 13.7%) and controls (45.6%, 39.5% and 14.9%, respectively) and the frequencies of CT60 A/A, A/G, and G/G genotypes in the patient (42.4%, 37.0% and 20.6%) and the control (38.6%, 40.4% and 21.0%, respectively) groups were not significantly different. The frequencies of various haplotypes including genetic loci +49A/G and CT60 and frequencies of G alleles at these positions were comparable between patient and the control groups and its presence did not correlate with clinical and biochemical indices of the disease. None of the patients had APECED-related AIRE gene mutations. Lack of significant difference in the pattern of CTLA-4 A/G(49) and/or CT60A/G genotypes and absence of common APECED syndrome-related AIRE gene mutations among patients and controls suggest that these sites do not play a role in the development of the SIH.

Parathyroid hormone gene polymorphism and sporadic idiopathic hypoparathyroidism

The pathogenetic mechanisms involved in the development of sporadic idiopathic hypoparathyroidism are currently under investigation. Although autoantibodies against the calcium-sensing receptor (CaSR) have been implicated to play a role, these could be demonstrated in only 49% of a group of 51 patients with sporadic idiopathic hypoparathyroidism that we previously studied. Therefore, we investigated 49 of these patients further, regardless of their antibody status, and looked for mutations in the section of the PTH gene sequence that coded for prepro-PTH as well as the 3'-untranslated region (3'-UTR) of the gene, which is believed to be involved in the stability of its mRNA. We also examined the relationship between the clinical manifestations of the disease and the occurrences of two commonly observed single nucleotide polymorphisms (SNPs) in the PTH gene. In 49 of the patients with idiopathic hypoparathyroidism and in 55 healthy controls, the SNPs were characterized by restriction analysis using DraII and BstBI enzymes. In a subset of these patients, exons 2 and 3 of the PTH gene (n = 37) and its 3'-UTR region (n = 40) were also sequenced. No mutations were observed in the segment of the PTH gene coding for the signal peptide, prohormone, or the 3'-UTR region. However, three well described SNPs were observed: 1) an A-->G substitution in intron 1 in 35.1% of the patients; 2) a G-->A substitution in intron 2, characterized by BstBI, in one or both alleles in 27%; and 3) a C-->A substitution at codon 52 (CGA) of exon 3, characterized by DraII, in one or both alleles in 59.7% of the patients. There was no significant difference in the frequency of occurrence of these SNPs between the patient and the control groups. Furthermore, the mean age at onset of symptoms, body mass index, frequency of cataract, tetany, convulsion, basal ganglia calcification, serum calcium, inorganic phosphorus, and intact PTH were not significantly different between patients with and without the above-described SNPs. Thus, the data from this report demonstrate that in patients with sporadic idiopathic hypoparathyroidism, neither the clinical manifestations nor the biochemical indexes of the disease are related to the occurrence of mutations or SNPs in the PTH gene. Because neither patient nor control samples exhibited any variations in the sequence of their 3'-UTR regions, it is unlikely that mRNA instability is a factor in the pathogenesis of the disease. Additional studies are required to investigate the role of other genes and autoantigens that may be involved in the genesis of idiopathic hypoparathyroidism.