PTH/PTHrP receptor and pseudohypoparathyroidism

The PTH/PTHrP receptor, a G protein coupled receptor, mediates the actions of PTH and PTHrP. Homozygous inactivating mutations in this receptor cause a rare disorder called Blomstrand chondrodystrophy. Since this disease is lethal in utero or perinatal period, the existence of PTH resistance has not been verified. Inactivating mutations in PTH/PTHrP receptor have not been found in the patients with pseudohypoparathyroidism (PsH), a group of disorders characterized by biochemical hypoparathyroidism and unresponsiveness to PTH. In patients with PsH type Ia, numerous heterozygous inactivating mutations have been identified in the gene (GNAS1) encoding the alpha-subunit of Gs protein (Gs alpha) which couples multiple receptors to the stimulation of adenylate cyclase. It is suggested that some abnormality in GNAS1 outside the coding exons may lead to PsH type Ib. To explain the heredity and phenotypic variation of PsH, tissue- or cell-specific imprinting of Gs alpha has been implicated.     

A new approach to imprinting mutation detection in GNAS by Sequenom EpiTYPER system

BackgroundPseudohypoparathyroidism type Ib (PHPIb) results from abnormal imprinting of GNAS. Familial and sporadic forms of PHPIb have distinct GNAS imprinting patterns: familial PHPIb patients have an exon A/B-only imprinting defect and an intragenic STX16 deletion, whereas sporadic PHPIb cases have abnormal imprinting of the three differentially methylated regions (DMRs) in GNAS without the STX16 deletion. Overall GNAS methylation defects have recently been detected in some PHPIa patients.MethodsThis study describes the first quantitative methylation analysis of multiple CpG sites for three different GNAS DMRs using the Sequenom EpiTYPER in 35 controls, 12 PHPIb patients, 2 PHPIa patients and 2 patients without parathormone (PTH) resistance but having only hypocalcemia and hyperphosphatemia.ResultsAll patients have GNAS methylation defects typically with NESP hypermethylation versus XL and exon A/B hypomethylation while the imprinting of SNURF/SNRPN was normal. PHPIa patients showed an abnormal methylation in the three DMRs of GNAS. For the first time, a marked abnormal GNAS methylation was also found in 2 patients without PTH resistance but having hypocalcemia and hyperphosphatemia.ConclusionsThe Sequenom EpiTYPER proves to be very sensitive in detecting DNA methylation changes. Our analysis also suggests that GNAS imprinting defects might be more frequent and diverse than previously thought.     

The molecular basis of renal amyloidosis in Irish-American and Polish- Canadian kindreds

Hereditary amyloidosis of an unusual form has been reported in two separate kindreds; one was Polish-Canadian and the other was Irish- American (Am J Med 1975; 59:121 and Trans Assoc Am Physicians 1981; 94:211). In both kindreds, affected members developed hypertension and nephrotic syndrome due to amyloidosis in their forties or fifties, but the genetic background responsible for the condition has been left undetermined. To identify the genetic defect in these kindreds, a portion of exon 5 of the fibrinogen alpha-chain gene in members of these kindreds was examined for a mutation by single-strand conformation polymorphism analysis and direct DNA sequencing. DNA analyses revealed an A-->T transversion at the second base of codon 526 of the fibrinogen alpha-chain gene in both of these kindreds. Analysis of DNA polymorphisms in the fibrinogen alpha-chain gene locus (TCTT repeat in intron 3, Rsal site in exon 5, and Taql site in the 3' flanking region of the gene) showed the haplotype B5-Rsal(+)-Taql(-) for the Val 526 mutant gene in both kindreds studied here, as well as in two kindreds previously described (J Clin Invest 1994; 93:731). The fibrinogen alpha-chain gene mutation (Val 526) is the genetic defect responsible for hereditary renal amyloidosis in these two kindreds, and the mutant genes in the Val 526 kindreds may have been derived from a single founder.      

Related individuals with different androgen receptor gene deletions.

We have identified different members of one family affected by androgen insensitivity syndrome who have deletions of different exons of the X-linked androgen receptor (AR) gene. Two affected (XY) siblings have a deletion of exon E of the AR gene and their affected (XY) aunt has a normal exon E, but a deletion of exons F and G of the same gene. The mother and maternal grandmother of the children both carry the exon E deletion, but not the exon F, G deletion. Both deletions are 5 kb in length and have one breakpoint within a 200-bp region in intron 5; however, they extend in opposite directions. The probability that these two different deletions have arisen at random is extremely low, but the cause of this intriguing phenomenon remains to be found.     

Change in the spectrum of RET mutations diagnosed between 1994 and 2006

Medullary thyroid carcinoma (MTC) is a rare calcitonin producing tumor. About 70-75% of patients with MTC have sporadic disease while the others suffer from hereditary MTC. Hereditary MTC is divided into three clinical subtypes: multiple endocrine neoplasia (MEN) type 2A is characterized by MTC, pheochromocytoma and primary hyperparathyroidism. MEN 2B is characterized by aggressive MTC, pheochromocytoma, marfanoid habitus and the presence of distinctive mucosal neuromas on the tongue, lips and subconjunctival areas as well as ganglioneuromatosis of the gastrointestinal tract. The third clinical subtype of inherited MTC, familial MTC, is defined as the presence of MTC in families without evidence of adrenal or parathyroid gland involvement. Hereditary MTC is caused by autosomal dominant gain-of-function mutations in the RET proto-oncogene. The first RET germline mutations were identified in 1993 in patients with MEN 2A and FMTC. Initially a codon 634 (exon 11) mutation was found in approximately 85% of patients with MEN 2A, and germline mutations in FMTC kindreds were more equally distributed throughout the RET proto-onocogene. In about 5% of families in these earlier series, mutations did not reside in exons 10 and 11. We now report a change in the spectrum of mutations detected in the RET proto-oncogene in patients with hereditary MTC from the 'classical' mutation at codon 634 in exon 11 (level 2) to more cases with mutations in the exons 13-15 (level 1) and less aggressive disease. In our series 38.9% of mutations were level 1 mutations, 54.4% level 2, and 5.6% level 3 mutations.     

假性甲状旁腺功能减退症Ⅰa型临床与基因分析

目的总结假性甲状旁腺功能减退(PHP)Ⅰa型临床特点,并探讨其分子发病机制。方法收集临床资料,抽取先证者及家系成员外周血,通过PCR扩增与直接测序检测GNAS基因。结果 3例先证者临床表现及实验室检查均符合PHP-Ⅰa型,家系成员无异常表现。基因测序发现2个SNP位点,分别位于第二外显子c.212A>C(p.E71D),第五外显子c.393C>T(p.I131I)。结论假性甲状旁腺功能减退较罕见,但根据实验室检查结果及临床特点,可与原发性癫痫相鉴别,减少误诊率。PHP-Ⅰa型分子遗传机制尚需进一步探讨。     

Screening of nineteen unrelated families with generalized resistance to thyroid hormone for known point mutations in the thyroid hormone receptor beta gene and the detection of a new mutation.

Generalized resistance to thyroid hormone (GRTH) is a syndrome characterized by impaired tissue responsiveness to thyroid hormone. Two distinct point mutations in the hormone binding domain of the thyroid hormone receptor (TR) beta have recently been identified in two unrelated families with GRTH. One, Mf, involves a replacement of the normal glycine-345 for arginine in exon 7 and another, Mh, replaces the normal proline-453 for histidine in exon 8. To probe for the presence of the Mf and Mh defect in 19 unrelated families with GRTH, we applied separate polymerase chain reactions using allele-specific oligonucleotide primers containing the normal and each of the two mutant nucleotides at the 3'-position. A total of 24 affected subjects and 13 normal family members were studied. The mode of inheritance was dominant in 13 families, was unknown in 5 families, and was clearly recessive in 1 family in which only the consanguineous subjects were affected. Primers containing the substitutions specific for Mf and Mh amplified exons 7 and 8, respectively, only in affected members of each of the two index families. Primers containing the normal sequences amplified exons 7 and 8 of the TR beta gene in all subjects except affected members of one family. In this family with recessively inherited GRTH, neither exon could be amplified using any combinations of primers and DNA blot revealed absence of all coding exons. These results indicate a major deletion of the TR beta gene, including both DNA and hormone binding domains. Since heterozygous members of this family are not affected, the presence of a single normal allele is sufficient for normal function of the TR beta. These data also support the hypothesis that in the dominant mode of GRTH inheritance the presence of an abnormal TR beta interferes with the function of the normal TR beta. Distinct mutations are probably responsible for GRTH in unrelated families.     

A base mutation of the C-erbA beta thyroid hormone receptor in a kindred with generalized thyroid hormone resistance. Molecular heterogeneity in two other kindreds.

Generalized thyroid hormone resistance (GTHR) is a disorder of thyroid hormone action that we have previously shown to be tightly linked to one of the two thyroid hormone receptor genes, c-erbA beta, in a single kindred, A. We now show that in two other kindreds, B and D, with differing phenotypes, there is also linkage between c-erbA beta and GTHR. The combined maximum logarithm of the odds score for all three kindreds at a recombination fraction of 0 was 5.77. In vivo studies had shown a triiodothyronine (T3)-binding affinity abnormality in nuclear receptors of kindred A, and we therefore investigated the defect in c-erbA beta in this kindred by sequencing a major portion of the T3-binding domain in the 3'-region of fibroblast c-erbA beta cDNA and leukocyte c-erbA beta genomic DNA. A base substitution, cytosine to adenine, was found at cDNA position 1643 which altered the proline codon at position 448 to a histidine. By allelic-specific hybridization, this base substitution was found in only one allele of seven affected members, and not found in 10 unaffected members of kindred A, as expected for a dominant disease. Also, this altered base was not found in kindreds B or D, or in 92 random c-erbA beta alleles. These results and the fact that the mutation is predicted to alter the secondary structure of the crucial T3-binding domain of the c-erbA beta receptor suggest this mutation is an excellent candidate for the genetic cause of GTHR in kindred A. Different mutations in the c-erbA beta gene are likely responsible for the variant phenotypes of thyroid hormone resistance in kindreds B and D.     

Differential expression of mutant and normal beta T3 receptor alleles in kindreds with generalized resistance to thyroid hormone.

Thyroid hormone resistance (THR) is primarily an autosomal dominant inherited disease characterized by resistance of pituitary and peripheral tissues to the action of thyroid hormone. We investigated whether the heterogeneous phenotypic features that occur not only among kindreds but also within the same kindred might be due to the expression of differing ratios of mutant and normal receptors in tissues. Using an allele-specific primer extension method, we determined the relative expression of normal and mutant mRNAs from the fibroblasts of affected and unaffected members of two kindreds with TRH: A-H and N-N. While two affected members of A-H, as expected, had nearly equal amounts of normal and mutant hTR beta mRNA, two other members had mutant mRNA levels that accounted for at least 70% of the hTR beta mRNA. Phenotypic variability within and between kindreds with generalized resistance to thyroid hormone GRTH may be due to this differential expression of the mutant and wild type mRNA. Furthermore, when several clinical parameters of THR were compared in several affected members from two kindreds with GRTH, we found that two cases in one kindred exhibited a high mutant-to-normal hTR beta ratio and had considerably more bone resistance during their development. In certain kindreds with THR, differing ratios of normal and mutant hTR receptors may be age and growth related and may account for the reported attenuation of phenotypic symptoms with age.     

Human factor IXLincoln Park: a molecular characterization

Using genomic DNA prepared from peripheral blood samples of a patient with factor IX deficiency, all eight exons as well as sequences around the splice junctions and putative promoter region of human factor IX DNA have been subjected to polymerase chain reaction (PCR) amplification and sequenced. Comparison of these sequences with normal factor IX gene sequences revealed an insertion in exon VIII that resulted in the alteration of 11 amino acids and the addition of 23 amino acids, all at the carboxy terminal of factor IX. This insertion destroys an Msp I restriction site; carrier detection and antenatal diagnosis in affected kindreds can be performed by testing for the absence of this site. This is the first characterization of a mutation in which insertion in the carboxy terminal region of factor IX causes factor IX deficiency. The genetic change in factor IX in this patient is called Factor IXLincoln Park.     

Hereditary renal amyloidosis with a novel variant fibrinogen.

Two families with hereditary renal amyloidosis were found to have a novel mutation in the fibrinogen A alpha chain gene. This form of amyloidosis is an autosomal dominant condition characterized by proteinuria, hypertension, and subsequent azotemia. DNAs of patients with amyloidosis were screened for a polymorphism in fibrinogen A alpha chain gene by single-strand conformation polymorphism analysis, and affected individuals from two kindreds were found to have a mutation. Both of these kindreds are American of Irish descent presenting with non-neuropathic, nephropathic amyloidosis in the fifth to the seventh decade of life. DNA sequencing showed a point mutation in the fibrinogen A alpha chain gene that is responsible for substitution of valine for glutamic acid at position 526. By restriction fragment length polymorphism analysis, 7 affected individuals and 14 asymptomatic individuals in these two kindreds were positive for the fibrinogen A alpha chain Val 526 gene. Fibrinogen was isolated from plasma of a heterozygous gene carrier and shown to contain approximately 50% variant fibrinogen. Discovery of this new mutation confirms the association between fibrinogen A alpha chain variant and hereditary renal amyloidosis and establishes a new biochemical subtype of amyloidosis.     

蛋白C基因新突变His134Asn所致Ⅰ型蛋白C缺乏症

目的：研究一家族性血栓病相关病因的表型及基因型。方法：先证者、其母、二兄分别在３５，１９，３３岁起无明显诱因患反复性下肢深静脉血栓（ＤＶＴ）。对其四代１３个家庭成员的抗凝血酶Ⅲ、蛋白Ｃ（ＰＣ）、蛋白Ｓ（ＰＳ）、纤溶酶原的抗原和活性及活化的ＰＣ抗性等进行检测。结果：该家族５个成员患有Ⅰ型杂合子ＰＣ缺乏症（ＰＣ抗原和活性降低５０％左右）。ＰＣ基因各外显子及外显子、内含子连接区聚合酶链反应－单链构象多态性（ＰＣＲ－ＳＳＣＰ）未发现明显的异常带；亚克隆后测序发现ＰＣ的第Ⅵ外显子３４４４Ｃ→Ａ导致１３４Ｈｉｓ→Ａｓｎ变异，这是国外尚未报道的新突变，被命名为ＰＣ长沙。此突变使限制性内切酶ＨｐｈⅠ位点丧失，用ＰＣＲ／ＨｐｈⅠ进行家系分析，证实了６个家系成员（包括５个ＰＣ缺乏者）具有同样的突变。结论：Ｈｉｓ１３４Ａｓｎ是此家族ＰＣ缺乏所致ＤＶＴ的密切相关病理基因型。     

The white gene of the tephritid fruit fly Bactrocera tryoni is characterized by a long untranslated 5' leader and a 12 kb first intron

A 300 bp fragment from exon 6 of the white gene of Bactrocera tryoni was used to screen a B. tryoni genomic library. One positive (∼14 kb) insert contained exons 2–6 of white by nucleotide and amino acid sequence similarity to the white genes of D. melanogaster (O'Hare et al ., 1984; Pepling & Mount, 1990). Lucilia cuprina (Garcia et al ., 1996). Ceratitis capitata (Zwiebel et al ., 1995) and Anopheles gambiae (Besansky et al ., 1995). A white 5' cDNA fragment containing exons 1, 2 and part of exon 3 was amplified, cloned and sequenced. An inverse PCR fragment of genomic DNA was generated, containing the exon 1 coding region plus ∼2.1 kb of upstream sequence, encompassing the putative promoter of the gene. Exon 1 was found to be 728 bp long, encoding the first twenty-five amino acids. The full length of intron 1 was shown to be 12 kb (amplified using long PCR protocols), up to 3 times the length of the longest white intron 1 isolated to date.     

An amino acid substitution in the putative second extracellular loop of RBC band 3 accounts for the Froese blood group polymorphism

BACKGROUND: The low incidence RBC antigen Fr(a) has been excluded from 17 of the 25 established blood group systems. Previous genetic analysis assigned the gene controlling Fr(a) expression to the same chromosomal region as the solute carrier family 4, anion exchanger member 1 gene (SLC4A1). Because SLC4A1 encodes RBC band 3 and controls the expression of Diego blood group system antigens, the possible relationship of Fr(a) to the Diego blood group system was investigated by molecular analysis of SLC4A1. STUDY DESIGN AND METHODS: Blood samples were obtained from the members of two unrelated Mennonite kindreds segregating for Fr(a). DNA was extracted, amplified by PCR using intronic primer sets flanking exons 11-20 of SLC4A1, and screened by single-strand conformation polymorphism (SSCP) analysis. Those exons displaying SSCPs were subjected to DNA sequence analysis. RESULTS: An exon 13 SSCP mobility shift was observed in the DNA from all Fr(a+) persons that was not seen in the DNA from Fr(a-) family members or control subjects. Linkage between the exon 13 SSCP and FR:(a) was established, with peak lods = 3.62 at theta = 0.00 for combined paternal and maternal meioses. DNA sequencing revealed a GAG --> AAG mutation that underlies a Glu480Lys substitution in RBC band 3. CONCLUSIONS: A point mutation in exon 13 of SLC4A1 accounting for a Glu480Lys substitution in band 3 controls Fr(a) expression. On the basis of these our results, the International Society of Blood Transfusion Working Party on Terminology for Red Cell Surface Antigens has assigned Fr(a) to the Diego blood group system, with the designation DI20.     

Genomic organization of the mouse pore-forming protein (perforin) gene and localization to chromosome 10. Similarities to and differences from C9

Genomic clones encompassing the entire coding region of the mouse lymphocyte pore-forming protein gene (Pfp) have been isolated and used to determine its intron-exon organization. In contrast to C9, Pfp has a simple structure, consisting of only three exons (two of which encode polypeptide), a large 5' intron, and a single, smaller intron that is situated approximately one-third of the way through the protein-coding portions of the gene. The regions encoding the homologous domains of PFP and C9 are encoded on exons 7, 8, 9, and 10 of C9, but form only approximately half of the open reading frame of exon III in Pfp. Although encoding polypeptides with related functions, the two genes possess such sharply contrasting structures as to suggest that their analogous regions may have risen independently, by a process of convergent evolution. Using a panel of somatic cell hybrid cell lines, Pfp has been mapped to chromosome 10.     

Characterization of seven novel mutations of the c-erbA beta gene in unrelated kindreds with generalized thyroid hormone resistance. Evidence for two "hot spot" regions of the ligand binding domain.

Genetic analysis in our laboratory of families with generalized thyroid hormone resistance (GTHR) has demonstrated tight linkage with a locus, c-erbA beta, encoding a nuclear T3 receptor. Three point mutations and two deletions in this locus have previously been reported in affected individuals in unrelated families as potential molecular bases for this disorder. In the present study, we have used direct sequencing of polymerase chain reaction-amplified exons of the c-erbA beta gene to rapidly identify novel point mutations from seven previously uncharacterized kindreds with GTHR. Six single base substitutions and one single base insertion were identified and found to be clustered in two regions of exons 9 and 10 in the ligand binding domain of the receptor: in the distal ligand-binding subdomain L2 and across the juncture of the taui and dimerization subdomains. Reduction of T3-binding affinity in each of four mutations tested as well as segregation of all mutations to clinically affected individuals strongly supports the hypothesis that these changes are the cause of GTHR in these kindreds. In view of the diversity of clinical phenotypes manifested, the distinct topographic clustering of the mutations provides an invaluable genetic tool for the molecular dissection of thyroid receptor function.     

Urinary cyclic 3',5'-adenosine monophosphate responses to exogenous and endogenous parathyroid hormone in familial benign hypercalcemia and primary hyperparathyroidism

FBH is characterized by symptomless hypercalcemia, low urinary calcium excretion, normal iPTH values, generally normal parathyroid histology, and failure of subtotal parathyroidectomy is normalize serum calcium. We studies six patients with FBH from three kindreds, six patients with sporadic 1 omicron HPT, and six healthy volunteers. To characterize the renal response to PTH, 14 of the subjects had infusions of bovine PTE (300 U intravenously over 15 min) and, separately, stimulation of endogenous PTH release by infusion of disodium EDTA (50 mg/kg over 2 hr). PTE induced striking increases of UcAMP (nM/100 ml of GF) that were indistinguishable between controls and subjects having FBH. However, the rise of UcAMP in 1 omicron HPT was significantly reduced (p < 0.001) compared to controls or the FBH group. EDTA-induced hypocalcemia raised serum iPTH and UcAMP in all three groups; the increases of iPTH (two assays of differing specificity) were greatest in 1 omicron HPT and least in FBH. In contrast, increases of UcAMP were greatest in FBH and 1 omicron HPT and indistinguishable from one another. The increase of UcAMP considered as a function of the increase in PTH showed significantly greater UcAMP responses in FBH than in the other groups. These results are consistent with primary or secondary alterations of renal responsiveness to PTH in both FBH and 1 omicron HPT, which may in part explain the different renal tubular calcium handling in the two conditions.     

Vitamin D deficiency and renal calcium transport in the rat.

To examine the role of vitamin D in the renal tubular handling of calcium, clearance studies were performed in three groups of rats: group A rats fed a standard vitamin D-deficient diet (Ca 0.45%, P 0.3%) for 6 wk, were hypocalcemic with secondary hyperparathyroidism; group B rats fed the same diet as in group A but with high calcium (Ca 1.4%) and 20% lactose, were normocalcemic and without secondary hyperparathyroidism; group C rats fed the same diet as in group A but supplemented with 25 U of vitamin D3 orally twice a week, were normocalcemic, vitamin D-replete, and euparathyroid. After thyroparathyroidectomy (TPTX), each rat was infused intravenously with an electrolyte solution that contained a fixed concentration of calcium (0-30 mM) with or without parathyroid hormone (PTH; 0.75 or 2.5 U/h) at a rate of 3 ml/h. Urinary calcium excretion and serum calcium concentrations were measured between 16 and 19 h of the infusion, and the apparent threshold of calcium excretion was determined. The threshold of calcium excretion was lower in vitamin D-deficient TPTX rats (groups A and B) than in vitamin D-replete TPTX rats (group C), and not different between group A and group B. Administration of PTH at a dose of 0.75 U/h increased the threshold of calcium excretion by approximately 0.6 mM in group C, but did not alter the threshold either in group A or group B. Administration of a higher dose of PTH (2.5 U/h) raised the threshold similarly in both group A and group B to the extent comparable with that in group C, when it was given 0.75 U/h of PTH. These results demonstrate that the renal threshold of calcium excretion is decreased in the vitamin D-deficient rats independent of the secondary hyperparathyroidism, and that the higher dose of PTH was necessary to raise the calcium threshold in vitamin D-deficient rats. Thus, present study indicates the presence of dual effects of vitamin D on renal tubular handling of calcium; the one is to facilitate renal calcium reabsorption and the other is to enhance the responsiveness of the tubule to PTH.     

Nephritogenic antigen determinants in epidermal and renal basement membranes of kindreds with Alport-type familial nephritis.

We probed epidermal basement membranes (EBM) of acid-urea denatured skin from members of kindreds with Alport-type familial nephritis (FN) for the presence of antigens reactive with Goodpasture sera (GPS) and serum (FNS) from an Alport patient who developed anti-glomerular basement membrane (GBM) nephritis in a renal allograft. By immunoblotting, GPS reacted primarily with the 28,000 molecular weight (mol wt) monomer but also the 24,000 mol wt and 26,000 mol wt monomers of the noncollagenous globular domain (NC1) of type IV collagen from normal human GBM, while FNS identified only the 26,000-mol wt monomer. FNS reacted with EBM of 12 controls and nine unaffected male kindred members but not EBM of eight affected males. Five affected females exhibited interrupted reactivity of FNS with EBM. GPS showed variable reactivity with EBM and was not discriminating with respect to Alport-type FN. FNS did not stain renal basement members of five affected males. However, the EBM, tubular basement membrane, and Bowman's capsules of affected males contained antigens reactive with GPS. These immunochemical studies suggest that the FNS antigen is distinct from Goodpasture antigen(s). The expression of FNS antigen located on the NC1 domain of type IV collagen is altered in basement membranes of patients with Alport-type FN, and the distribution of this antigenic anomaly within kindreds suggests X-linked dominant transmission of a defective gene.