A maternal Epimutation of
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- Molecular analysis of the GNAS gene
- Characterization of the G
- Epigenetic characterization of the GNAS DMRs
- Albright F, Burnett CH, Smith PH, Parson W
- Weinstein LS, Gejman PV, Friedman E, Kadowaki T, Collins RM, Gershon ES, Spiegel AM
- Linglart A, Carel JC, Garabedian M, Le T, Mallet E, Kottler ML
- Liu J, Erlichman B, Weinstein LS
- Liu J, Litman D, Rosenberg M, Yu S, Biesecker L, Weinstein L
- A, Crawford JD, Ju¨ppner H
- Linglart A, Gensure RC, Olney RC, Juppner H, Bastepe M
- Bastepe M, Fro¨hlich LF, Linglart A, Abu-Zahra HS, Tojo K, Ward LM, Ju¨- ppner H
- Bastepe M, Gunes Y, Perez-Villamil B, Hunzelman J, Weinstein LS, Ju¨ppner H
- Linglart A, Mahon MJ, Kerachian MA, Berlach DM, Hendy GN, Juppner H, Bastepe M
- Ischia R, Lovisetti-Scamihorn P, Hogue-Angeletti R, Wolkersdorfer M, Win- kler H, Fischer-Colbrie R
- Plagge A, Isles AR, Gordon E, Humby T, Dean W, Gritsch S, Fischer-Colbrie R, Wilkinson LS, Kelsey G
- Germain-Lee EL, Schwindinger W, Crane JL, Zewdu R, Zweifel LS, Wand G, Huso DL, Saji M, Ringel MD, Levine MA
- Bastepe M, Weinstein LS, Ogata N, Kawaguchi H, Ju¨ppner H, Kronenberg HM, Chung UI
- Hayward B, Kamiya M, Strain L, Moran V, Campbell R, Hayashizaki Y, Bonthron DT
A Maternal Epimutation of GNAS Leads to Albright Osteodystrophy and Parathyroid Hormone Resistance Virginie Mariot,* Ste´phanie Maupetit-Me´houas,* Christiane Sinding, Marie-Laure Kottler, and Agne`s Linglart Institut National de la Sante´ et de la Recherche Me´dicale U561 (V.M., S.M.-M., C.S., A.L.) and Paediatric Endocrinology (A.L.), Paris V University, St-Vincent de Paul Hospital, 75014 Paris, France; and Department of Genetic and Human Reproduction (M.-L.K.), Centre Hospitalier Universitaire, 14033 Caen, France
maternal loss-of-function mutations of GNAS, the gene encoding G ␣ s
␣-stimulatory subunit of the G protein. Affected individuals display hormonal resistance (mainly PTH and TSH resistance) and Albright hereditary osteodystrophy. PHP type Ib (PHP-Ib), usually defined by isolated renal resistance to PTH and sometimes mild TSH resistance, is due to a maternal loss of GNAS exon A/B methylation, leading to decreased G ␣ s expression in specific tissues. Objective and Results: We report a girl with obvious Albright osteodystrophy features, PTH re- sistance, normal G ␣ s
coding sequence (exons 1–13). The methylation analysis of the four GNAS differentially methylated regions, i.e. NESP, AS, XL, and A/B, revealed broad methylation changes at all differentially meth- ylated regions, including GNAS exon A/B, leading to a paternal epigenotype on both alleles.
␣ s due to GNAS epimutations is not restricted to the renal tubule but may affect nonimprinted tissues like bone; 2) PHP-Ib is a heterogeneous disorder that should lead to studying GNAS epigenotype in patients with PHP and no mutation in GNAS exons 1–13, regardless of their physical features. (J Clin En- docrinol Metab 93: 661– 665, 2008) T he association of hypocalcemia, hyperphosphatemia, and elevated PTH levels in the absence of vitamin D deficiency defines PTH resistance and pseudohypoparathyroidism (PHP). The main form of PHP, PHP type Ia (PHP-Ia), is usually de- scribed as the association of Albright hereditary osteodystrophy (AHO) (a collection of physical features such as obesity, brachymetacarpy, brachymetatarsy, short stature, sc ossifica- tions, and some degree of mental retardation) and resistance to hormones sharing a signaling pathway through G protein-cou- pled receptors (PTH, TSH) (1, 2). Most of the PHP-Ia affected patients carry a maternal loss of function of GNAS, the gene encoding G ␣ s , the ␣-stimulatory subunit of the G protein (3, 4). An approximate 50% decrease in G ␣ s bioactivity was found in the cells of most of these patients (2). Few patients exhibit normal G ␣
bioactivity with GTP ␥S (the nonhydrolyzable guanine nu- cleotide analog) as a stimulant in red blood cells, despite a ma- ternal loss of function mutation at the C terminal part of G ␣ s
likely affecting exclusively the G ␣ s -receptor interaction (4). In contrast, PHP type Ib (PHP-Ib) is usually characterized by isolated hormonal resistance, mainly PTH and sometimes TSH resistance and the lack of AHO (5). In affected PHP-Ib individ- uals, Liu et al. (6) identified methylation changes at the GNAS differentially methylated regions (DMRs), including GNAS exon A/B (also referred to as exon 1A), as the cause of the de- creased G ␣ s
thyroid), therefore hormonal resistance. In addition, microdele- 0021-972X/08/$15.00/0 Printed in U.S.A. Copyright © 2008 by The Endocrine Society doi: 10.1210/jc.2007-0927 Received April 24, 2007. Accepted December 20, 2007. First Published Online January 8, 2008 * V.M. and S.M.-M. contributed equally to this work and should be regarded as joint first authors.
Abbreviations: AHO, Albright hereditary osteodystrophy; CTRL, control; DMR, differen- tially methylated region; PHP, pseudohypoparathyroidism; PHP-Ia, PHP type Ia; PHP-Ib, PHP type Ib. S P E C I A L F E A T U R E C l i n i c a l C a s e S e m i n a r J Clin Endocrinol Metab, March 2008, 93(3):661– 665 jcem.endojournals.org 661 Downloaded from https://academic.oup.com/jcem/article-abstract/93/3/661/2597993/A-Maternal-Epimutation-of-GNAS-Leads-to-Albright by guest on 03 October 2017 tions within the STX16 gene (STXdel4 – 6 mat
, STXdel2– 4 mat
), located 220-kb upstream of GNAS exon A/B, have been found in most of the patients affected with the autosomal dominant form of PHP-Ib and exhibiting loss of GNAS exon A/B methyl- ation alone (7, 8). Deletions removing both NESP and AS exons (delNEPS55/ASdel3– 4 mat ) of GNAS have been identified in af- fected individuals of two unrelated families with PHP-Ib and broad GNAS methylation changes (9). The mechanism under- lying sporadic PHP-Ib with maternal broad GNAS methylation changes is yet undiscovered (Fig. 1). Because PHP-Ib appears to be a heterogeneous disorder, we investigated the epigenetic struc- ture of the GNAS gene in a girl presenting with PTH resistance, typical features of Albright osteodystrophy, normal G ␣ s bioac- tivity with GTP ␥S as a stimulant and no modification of the
Methods
The patient gave her informed consent for the genetic and epi- genetic analyses. Molecular analysis of the GNAS gene Genomic DNA was extracted from blood lymphocytes. The GNAS gene (exons 2–13) was PCR amplified and sequenced as described previously (4). Since the 2002 report (4), we have been able to amplify and sequence the GNAS exon 1 using the fol- lowing primers: forward, CCTCCCGGCCCGCGTGA, and re- verse, CTGCGGGGCGCCCTTCGA. The NESP and A/B re- gions were amplified from genomic DNA: A/B, forward GTCCGAAGATACGAAACTCC and reverse GCTGCCTAA- GAGTTAGCG; and NESP, forward CGAGTCTTAGGCT- GCGGAA and reverse ACAAGGAGAATCTGGACGGC.
␣
transcripts TotalRNAswereextractedfrombloodlymphocytes.AfterRT,the G ␣
transcripts were amplified using different primer pairs (exons 1–13, forward GGACAAGCAGGTCTACCG and reverse AGGG- TAGCAGTAGTGACGC; exons 4–13, forward CCTGAAAGAG- GCGATTGAAA and reverse AAGGTGCATGCGCTGAAT; and exons 1–8, forward AGACCGAGGACCAGCGCAA and reverse AGTCAGGACACGGCAGCGAA) and sequenced. The exons 1–8 PCR products were subcloned in a pcR4-Topo Cloning vector (In- vitrogen, Carlsbad, CA) and sequenced using a T7 primer. Epigenetic characterization of the GNAS DMRs GNAS DMRs were amplified by PCR from bisulfite-treated genomic DNA as described elsewhere (8). A/B was amplified using the primers: forward TTTTTTTGTTTTAGAGTTTTTAGGG and reverse
TAAAAATACAAAACCTC- CCCTACTC, then reamplified using the same primers. AS was first amplified using the prim- ers: forward TGTGTATATATTAAGGT- TATTAGGTG and reverse AAAAATTTTA- ATTAAAATTTAATACC, then reamplified using the primers: forward GGTGTGGG- TATTTATTTTTGGTTAGT and reverse TA- ATCAATCAACTCCTTTAACCCC. XL was amplified using the primers: forward GG- TAGTTTATTTTAAGAGGTTGTTA- GATTT and reverse AAAAAAATACTTTTC- CTCCCTCC. NESP was amplified using the primers: forward GAGGATAAAGATTTA- AGGGATTT and
reverse CTCAAA-
CTCCCCAATTTAAC. To assess the methylation status of the amplified regions, amplicons were submit- ted to BstUI digestion or sequenced. The FIG. 1. Simplified map of the 20q13.3 region (STX16 and the GNAS locus) and the localization of the known microdeletions causing PHP-Ib. GNAS is a complex imprinted locus yielding, besides G ␣ s
␣ s , NESP55, the A/B transcript, and the antisense (AS) transcript. NESP55, XL ␣ s , and A/B differ from G ␣ s only by their first exon. AS, XL ␣ s , and A/B are paternally derived transcripts, whereas NESP55 is a maternally derived transcript. Consistent with their monoallelic expression, the promoters of these imprinted transcripts are located within DMRs (18) (2). In contrast, the promoter giving rise to G ␣ s is not methylated, and accordingly, transcripts are derived in most tissues from both parental GNAS alleles. STX16, encoding Syntaxin16, is located 220-kb upstream of GNAS exon A/B and biallelically expressed (8). Exons are depicted as blackened rectangles, and direct repeats are shown as striped arrowheads. The deleted regions lie between the brackets; the location of the four DMRs studied are shown (
ϩ, methylated; -, unmethylated). Arrows indicate the origin of transcription. cen, Centromeric; Mat or m, maternal; Pat or p, paternal; tel, telomeric; X, XL ␣ s
FIG. 2. Patient’s phenotype. A, Height, weight, and body mass index (BMI) of the patient (black circle) and her parents and siblings (white circle and squares, respectively). B, Brachymetacarpy of the fourth and fifth metacarpals. 662 Mariot et al. Albright Osteodystrophy and GNAS Epimutation J Clin Endocrinol Metab, March 2008, 93(3):661– 665 Downloaded from https://academic.oup.com/jcem/article-abstract/93/3/661/2597993/A-Maternal-Epimutation-of-GNAS-Leads-to-Albright by guest
on 03 October 2017 NESP or XL amplicons were subcloned in a pcR4-Topo Cloning vector and sequenced using a T7 primer. Case Report When she was 10 yr old, the patient had generalized seizure revealing hypocalcaemia (1.4 m M , normal range 2.17–2.57). She was put on calcifediol, and 2 yr later, referred to our clinic for persistent hypocalcaemia. She was born from healthy noncon- sanguineous African-American parents. Her siblings are healthy (Fig. 2A). She was obese (body mass index Ͼ 97th centile at 12 yr and thereafter) with a round face. She controlled her weight gain through dietary adaptation. Her growth and pubertal develop- ment were normal [final height of 165 cm (target height of 162.5 cm), corresponding to the mean height of women in France], she had bilateral obvious brachymetacarpia affecting both hands (fourth and fifth metacarpals), and the metatarsals were normal. The x-rays confirmed the brachymetacarpia, showed the absence of distance enlargement between the L1 and L5 vertebral pedicles, and the absence of bone resorption features (Fig. 2B). We did not observe ectopic ossification clinically or on hands, feet, and spine x-rays. None of her siblings or parents had similar bone features. When she was 12 yr old, her laboratory tests showed: calce- mia 2.01 m M , phosphatemia 2.19 m M (normal range 0.8 –1.6), and PTH 399 pg/ml (normal range 10 –58). After exogenous PTH administration, the urinary cyclical AMP increased inad- equately (0.19 nmol/100 ml glomerular filtrate, normal range 0.59 –1.99), confirming the PTH resistance. She received alfa- calcidol (1- ␣-25 (OH) 2 D
) to prevent convulsions and normalize her blood calcium, phosphorus, and PTH. Despite alfacalcidol, 2 g daily, she never experienced elevated calciuria and main- tained her PTH levels within or close to the normal range. Free T 4 and TSH were measured at 12, 18, and 24 yr within the normal range. Because of the association of Albright osteodystrophy and PTH resistance, PHP-Ia was suspected, the biological activity of G ␣
was assessed in her red blood cells, as described previously (4), and found identical to control (CTRL) subjects (88% of three CTRL values, normal range 75–100%). Genetic and Epigenetic Findings The GNAS gene (exons 1–13) was amplified and sequenced (genomic DNA from blood lymphocytes), including the GC-rich exon 1, and no mutation was detected. However, three poly- morphisms were identified in the GNAS coding sequence: C/T, position 749 (exon 5) of NM000516; C/T, position 911 (exon 7) of NM000516; and C/T, position 1469 (exon 13) of NM000516 corresponding to the single nucleotide polymorphism rs8386. In addition, the G ␣ s
(exons 1–13) from the patient’s blood lymphocytes (Fig. 3). Di- rect nucleotide sequence of the G ␣ s
gosity at the polymorphic nucleotides 749, 911, and 1469 of the G ␣ s cDNA (the third is known as rs8386), indicating that two different alleles were amplified. Therefore, we have shown that both GNAS alleles are intact and expressed in the patient’s lym- phocytes, excluding large scale deletions of the GNAS coding region (exons 1–13). The exons 1– 8 PCR amplification of the G ␣
transcripts were subcloned and sequenced. Eight out of 14 clones carried the T and T (nucleotides 749 and 911 of NM000516, respectively). The remaining six clones carried the C and C nucleotides at the same location. After bisulfite treatment, GNAS exon A/B, NESP, XL, and AS were amplified and either submitted to enzymatic digestion, or sequenced (Fig. 4). In the absence of methylation, the DNA se- quence is modified by the bisulfite, removing the BstUI recog- nition sites (A/B, AS, NESP, and XL). Unlike the CTRL, and similarly to a PHP-Ib individual, the A/B, XL, and AS patient’s PCR products were not digested, indicating a loss of methylation of the A/B, XL, and AS patient’s maternal allele. Likewise, the NESP patient’s PCR product was almost fully digested, indicat- ing a gain of methylation of the NESP patient’s maternal allele. Direct nucleotide sequencing of the PCR products confirmed these results. The reported patient and the PHP-Ib individual chromatograms showed unmethylated DNA sequences of the A/B, XL, and AS PCR products, and methylated DNA sequences of the NESP PCR products. In summary, we found broad meth- ylation changes of the patient’s GNAS locus corresponding to a paternal epigenotype on both alleles (i.e. loss of GNAS exon A/B, XL, and AS methylation, and gain of NESP methylation). As expected, the patient did not carry the STXdel4 – 6 or the
␣ s . A, Amplification of G ␣ s (exons 4 –13) after RT of total RNAs extracted from the patient’s blood lymphocytes. B, Direct nucleotide sequence of the amplified G ␣ s transcripts of a CTRL individual (upper line) and our patient (lower line) displaying three heterozygous polymorphisms, using forward (749 and 911) and reverse (1469) sequencing primers. J Clin Endocrinol Metab, March 2008, 93(3):661– 665 jcem.endojournals.org 663 Downloaded from https://academic.oup.com/jcem/article-abstract/93/3/661/2597993/A-Maternal-Epimutation-of-GNAS-Leads-to-Albright by guest on 03 October 2017 STXdel2– 4. No polymorphisms were identified in the NESP and A/B regions of GNAS (59 –1114 of NM016592, 1076 –2054 of AF246983, respectively). Altogether, she was diagnosed as spo- radic PHP-Ib. Discussion The current report identifies an epigenetic mutation of GNAS in one girl with typical PTH resistance and features of Albright osteodystrophy. Direct nucleotide sequencing of the 13 exons of GNAS as well as amplification of G ␣ s transcripts issued from both alleles excluded the three types of defects usually associated with PHP-Ia: loss-of-function mutations, paternal unidisomy, or large deletions throughout the G ␣ s
did not identify any polymorphisms in the A/B or NESP regions, we cannot exclude a deletion in these regions as the cause of the observed paternal epigenotype in this patient. Deletion of the NESP and AS exons, associated with GNAS epigenetic changes, likely removing a regulatory element of GNAS methylation, has been described previously by Bastepe et al. (9). Findings similar to our patient are cur- rently reported by de Nanclares et al. (10) in five individuals with mild features of Albright osteodystrophy, i.e. shortness of metacarpals, short stature, ectopic ossification, and obe- sity. Our report confirms that Albright os- teodystrophy or at least brachymetacarpia and obesity are not specific symptoms of PHP- Ia, and that the epigenetic status of GNAS should be investigated in patients who show PTH resistance, normal G ␣ s bioactivity in blood cells, and the absence of genetic alter- ation of the GNAS exons 1–13, regardless of their phenotype. The imprinting defect observed in our pa- tient results in both alleles having a paternal- specific epigenotype characterized by a dra- matic decrease of methylation at exon A/B, XL, and AS promoter regions, therefore, likely biallelic expression of A/B, XL, and AS transcripts. Unfortunately, because XL is not expressed in blood lymphocytes, we were not able to amplify XL transcripts of this patient and identify their parental origin. The cause of this imprinting defect remains to be found. Because paternal expression of G ␣ s
icantly reduced in the thyroid, mild TSH re- sistance may appear in some patients with im- printing defects of the GNAS gene (5). Our patient does not exhibit TSH resistance so far. In such patients, the residual G ␣ s expression from both paternal imprinted alleles seems to allow a sufficient TSH signaling in thyroid cells. In addition, the potential increase in XL ␣
expression, a GNAS product known to share with G ␣ s
production through the stimulation of the TSH receptor (11, 12), may compensate for the lack of G ␣ s
In addition, the NESP promoter region appears fully meth- ylated in our patient and may result in a dramatic decrease of the NESP-specific transcripts. In humans, a specific role for the NESP transcript (expressed in adrenals and brain) has not yet been reported, and individuals with PHP-Ib do not seem to have detectable adrenal or neurological abnormalities (13, 14). Animal studies show that G ␣ s
chondrocytes and osteoblasts, and that despite the absence of bone phenotype in G ␣ s
drocytes with targeted monoallelic disruption of GNAS un- dergo premature hypertrophy (17). These data suggest that the PHP-Ia bone phenotype is related to a decrease of G ␣ s expression in the growth plate. Some features of AHO, par- ticularly brachydactyly and obesity, have now been observed in a small number of PHP-Ib patients, suggesting that im- printing defects of the GNAS gene may affect G ␣ s
in imprinted tissues (renal proximal tubule and thyroid) and in bone.
FIG. 4. Characterization of the GNAS broad methylation changes. A, Enzymatic digestion (BstUI) of the PCR amplified bisulfite-treated genomic DNA. The arrow shows the uncut allele (unmethylated); the CH3 arrow shows the cut allele (methylated). The affected PHP-Ib individual as well as the reported patient (Pt) display a loss of exon A/B, AS, and XL methylation, and gain of NESP methylation. B, Chromatograms of the XL PCR products. The PHP-Ib individual and patient chromatograms show unmethylated DNA sequences. On the other hand, the CTRL DNA displays heterozygosity, indicating the presence of two different alleles, one methylated and one unmethylated. C, To quantify the methylation status of the NESP and XL DMRs, the PCR products were subcloned and sequenced (in red, the methylated cytosines). Full circles represent a methylated CpG, and empty circles designate unmethylated CpG. Each row of circles represents a clone. Of the PHP-Ib individual and patient NESP CpG, 99.2% are methylated, whereas only 41.7% of the CTRL NESP CpG are methylated. Of the patient and PHP-Ib individual XL CpG, 10.7 and 7.9% are methylated, respectively, whereas 46.4% of the CTRL XL CpG are methylated. 664 Mariot et al. Albright Osteodystrophy and GNAS Epimutation J Clin Endocrinol Metab, March 2008, 93(3):661– 665 Downloaded from https://academic.oup.com/jcem/article-abstract/93/3/661/2597993/A-Maternal-Epimutation-of-GNAS-Leads-to-Albright by guest
on 03 October 2017 Acknowledgments We thank the patient for her kind contribution to this report. We also thank Pr. Bougne`res for his critical review and editorial help. Address all correspondence and requests for reprints to: Agne`s Linglart, Pediatric Endocrinology and Institut National de la Sante´ et de la Recherche Me´dicale U561, Hoˆpital St-Vincent de Paul, 82 avenue Denfert-Rochereau, 75014 Paris, France. E-mail: agnes.linglart@svp.aphp.fr. Disclosure Summary: The authors have nothing to declare. References 1. Albright F, Burnett CH, Smith PH, Parson W 1942 Pseudohypoparathyroid- ism–an example of “Seabright-Bantam syndrome.” Endocrinology 30:922– 932
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s ␣-subunit gene in Albright hereditary osteodystrophy detected by denaturing gradient gel electrophoresis. Proc Natl Acad Sci USA 87:8287– 8290 4. Linglart A, Carel JC, Garabedian M, Le T, Mallet E, Kottler ML 2002 GNAS1 lesions in pseudohypoparathyroidism Ia and Ic: genotype phenotype relation- ship and evidence of the maternal transmission of the hormonal resistance. J Clin Endocrinol Metab 87:189 –197 5. Liu J, Erlichman B, Weinstein LS 2003 The stimulatory G protein ␣-subunit G s
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␣-subunit (G s ␣) knockout mice is due to tissue-specific imprinting of the G s ␣ gene. Proc Natl Acad Sci USA 95:8715–8720 16. Germain-Lee EL, Schwindinger W, Crane JL, Zewdu R, Zweifel LS, Wand G, Huso DL, Saji M, Ringel MD, Levine MA 2005 A mouse model of albright hereditary osteodystrophy generated by targeted disruption of exon 1 of the Gnas gene. Endocrinology 146:4697– 4709 17. Bastepe M, Weinstein LS, Ogata N, Kawaguchi H, Ju¨ppner H, Kronenberg HM, Chung UI 2004 Stimulatory G protein directly regulates hypertrophic differentiation of growth plate cartilage in vivo. Proc Natl Acad Sci USA 101: 14794 –14799 18. Hayward B, Kamiya M, Strain L, Moran V, Campbell R, Hayashizaki Y, Bonthron DT 1998 The human GNAS1 gene is imprinted and encodes distinct paternally and biallelically expressed G proteins. Proc Natl Acad Sci USA 95:10038 –10043 J Clin Endocrinol Metab, March 2008, 93(3):661– 665 jcem.endojournals.org
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