The Journal of Clinical Endocrinology & Metabolism Vol. 88, No. 7 3043-3049
Copyright © 2003 by The Endocrine Society
Completely Skewed X-Inactivation in a Mentally Retarded Young Female with Pseudohypoparathyroidism Type IB and Juvenile Renin-Dependent Hypertension
Masashi Demura,
Yoshiyu Takeda,
Takashi Yoneda,
Kenji Furukawa,
Aiko Tachi and
Hiroshi Mabuchi
Second Department of Internal Medicine, School of Medicine, Kanazawa University, Kanazawa 920-8640, Japan
Address all correspondence and requests for reprints to: Masashi Demura, M.D., 13-1 Takara-machi, Kanazawa 920-8640, Japan. E-mail: fu21i8n3{at}sr.incl.ne.jp.
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Abstract
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Genetic analysis of the GNAS gene was performed in a patient with idiopathic renin-dependent hypertension, PTH resistance, and Albright’s hereditary osteodystrophy-like characteristics such as a round face, short stature, obesity, and mental retardation (IQ, 49). Mutational analysis showed no mutations in exons 1–13 or in any exon-intron boundary. However, methylation-status analysis revealed a bialleic methylation defect in GNAS exon 1A, indicating that a GNAS-imprinting defect is the cause of her PTH resistance, as commonly observed in pseudohypoparathyroidism type IB. The imprinting defect, however, could not explain her renin-dependent hypertension and Albright’s hereditary osteodystrophy-like phenotype. There are many types of X-linked mental retardation. Syndromic X-linked mental retardation, such as X-linked 
-thalassemia mental retardation syndrome and Rett syndrome, is reportedly associated with abnormal imprinting. To further investigate this unexplained phenotype, we tested whether this patient showed skewed X-inactivation (SXI) presumably as a result of postinactivation selection against cells with a mutated gene on the active X-chromosome. Completely SXI was observed in the DNA from her leukocytes, urinary sediment, and renal tissue. A mutation of the X-chromosome might be correlated with this phenotype because of a close association between completely SXI and X-chromosomal mutation.
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Introduction
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LYONIZATION REFERS TO the random inactivation of one of the two X-chromosomes in female mammalian cells during early embryonic development (1). Females are therefore mosaic for cell types in which either the paternal or maternal X-chromosome is active. Most females have a 50:50 distribution of cell types in which either parental chromosome is active. A deviation from this distribution may occur, however, and this is known as skewed X-inactivation (SXI). SXI may be the result of a selective disadvantage of cells with a lethal mutation in one X-chromosome (2, 3).
Pseudohypoparathyroidism (PHP) is a heterogeneous genetic disorder characterized by hypocalcemia and hyperphosphatemia due to PTH resistance. PHP is mainly classified into PHP type IA (PHPIA) with multihormone resistance and physical features of Albright’s hereditary osteodystrophy (AHO) and PHP type IB (PHPIB) with PTH resistance lacking other endocrine or physical abnormalities (4). PHPIA results from an inactivating mutation of the maternal GNAS gene (4), whereas PHPIB is almost always associated with a GNAS imprinting defect (4, 5).
We recently encountered a young female with PTH resistance accompanied with idiopathic juvenile hypertension and unusual physical features including a round face, short stature, obesity, and mental retardation. We performed a molecular genetic analysis of the GNAS gene in her genomic DNA and found an imprinting defect at the GNAS exon 1A, as commonly found in PHPIB (4, 5). Here, we demonstrate completely SXI of multiple tissues in this young patient with PHPIB, AHO-like phenotype, and idiopathic renin-dependent hypertension.
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Patient and Methods
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Patient profile
A 21-yr-old female patient was admitted in September 1994 to our department for investigation of hypertension with increased plasma-renin activity (PRA) and a history of hypertension since the age of 9 yr. Her blood pressure was 176/120 mm Hg. Grade 2 hypertensive retinopathy (Keith-Wagener classification) was seen without retinal edema, exudate, or hemorrhage. Serum creatinine was normal, and creatinine clearance ranged from 38–66 ml/min. The hormonal level in the renin-angiotensin axis was extremely increased (Table 1
). A captopril test (50 mg, orally) diminished her blood pressure from 168/117 to 134/92 mm Hg 90 min later and increased her PRA from 5.3–9.8 ng/ml·h, whereas her plasma aldosterone concentration (PAC) decreased from 254.9–84.5 pg/ml. These results indicated that her hypertension was renin-dependent.
To confirm the etiology of her renin-dependent hypertension, we performed detailed examinations consisting of renal angiography and renal vein sampling, renal biopsy, and systemic computed tomography (CT). No stenosis of renal arteries or their branches was found in a renal arteriogram. Venous renin activity was similarly increased everywhere without discrimination in renal vein sampling (Fig. 1). Therefore, renovascular hypertension was unlikely to be the cause of her renin-mediated hypertension. A percutaneous biopsy of the left kidney showed ischemic collapse of the glomerulus (Fig. 2A) and hyperplasia of the juxtaglomerular apparatus (Fig. 2B). Immunofluorescence showed negative staining for IgA, IgG, IgM, C3, C1q, and fibrinogen (data not shown). These pathological findings support a diagnosis of hypertensive nephrosclerosis and deny the possibility of renal parenchymal disease. Plasma and urinary catecholamines were normal (data not shown), and systemic CT revealed no neoplastic lesions, including pheochromocytoma and renin-producing tumors. Despite a likely relation between the patient’s hyperrenism and hyperplastic juxtaglomerular apparatus, we could not diagnose the cause of her renin-dependent hypertension. Follow-up renal angiography and vein PRA sampling 1 yr later were similar to the previous examinations on first admission. Repetitive CT and hormonal examinations have not yet disclosed any mass lesion. Her blood pressure has been well controlled by antihypertensive treatment; however, her PRA remains elevated. Fundoscopic findings and persistent hyperrenism ruled out malignant hypertension as a candidate explanation for her renin-dependent hypertension.
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FIG. 1. Venous sampling of renin activity. Increased renin activity was observed at all points. No laterality was detected.
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FIG. 2. Biopsy of the left kidney. A, Collapsed glomerulus with complete sclerosis. B, Glomerulus with a hypertrophied juxtaglomerular body (arrow). Hematoxylin-eosin stain; magnification, x400.
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The patient was a full-term infant and was delivered after an uncomplicated pregnancy. Her mother was healthy and without abnormal calcium metabolism [serum calcium, 9.8 mg/dl (reference range, 8.6–10.4 mg/dl); serum phosphate, 4.2 mg/dl (reference range, 2.2–4.4 mg/dl); plasma PTH, 44.1 pg/ml (reference range, 12–60 pg/ml); serum 1,25-(OH)2D, 41.9 pg/ml (reference range, 20–60 pg/ml)], and her father also was healthy by history only. Her parents were unrelated, and there was no family history of inheritable diseases. She is of short stature (152 cm) and weighs 66 kg. She showed an AHO-like phenotype, including short stature, obesity, round face, and mental deficits (IQ, 49) without brachydactyly or heterotopic calcifications. Her karyotype was normal (46,XX). Because of her AHO-like features, a detailed examination for PHP was performed. An elevated level of plasma PTH without hypocalcemia and hyperphosphatemia was found (Table 1
). Moreover, she showed slight urinary cAMP and phosphate elevation after injection of exogeneous human PTH-(1–34), indicating renal PTH resistance (Table 2). A diagnosis of PHP type I was based on laboratory findings (6). Treatment with 1,25-dihydroxyvitamin D3 was started, but her PTH remained elevated.
We investigated her resistance to TSH, LH, and FSH. There were no exaggerated TSH, LH, and FSH responses to their respective releasing hormones (data not shown), indicating that she had no additional resistance to these hormones. Her slightly increased TSH level (Table 1) was probably associated with the high circulating levels of autoantibodies to thyroglobulin and thyroid peroxidase, suggestive of chronic thyroiditis (data not shown).
The purpose of the study was explained to the patient and her mother, and their written informed consents were obtained.
Hormonal assay
The renin-angiotensin axis was assessed by using RIAs for PRA, angiotensin 1, angiotensin 2, and PAC, and an immunoradiometric assay for plasma renin concentration. Plasma-intact PTH was measured with a chemiluminescence immunoassay. Serum concentrations of vitamin D metabolites were evaluated with a RIA for 1,25-dihydroxyvitamin D and competitive-protein binding assays for 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D. Calcitonin was measured with an immunoradiometric assay. TSH, free T3, and free T4 were measured with enzyme immunoassays. LH and FSH were measured with electrochemiluminescence immunoassays.
PCR amplification and sequencing of the GNAS gene
Exons 1–13, 1A, and the flanking intron sequences of the GNAS gene were amplified by PCR from genomic DNA in peripheral blood leukocytes using the primer pairs shown in Table 3. The PCR products were sequenced using the ABI PRISM BigDye Terminator cycle sequencing kit (Applied Biosystems Japan, Tokyo, Japan). The sequencing reactions were performed according to the manufacturer’s instructions and were analyzed on an ABI310 DNA Sequencer (Applied Biosystems Japan).
Allelic expression of GNAS exon 1A
Total RNA was isolated from peripheral blood mononuclear cells. To examine allele-specific gene expression, 1 µg of total RNA was transcribed using Superscript II (Invitrogen Japan, Tokyo, Japan) and a random hexamer primer. Reverse transcribed products were amplified using specific primers (Table 3). The PCR occurred over 35 cycles. RT-PCR products were subcloned into pGEM-T Easy vector by TA cloning (Promega, Tokyo, Japan), and subclones were sequenced using T7 (5'-TAATACGACTCACTATAGGG-3') and M13R (5'-CAGGAAACAGCTATGAC-3') primers.
Methylation-specific PCR (MSP) and bisulfite genomic sequencing
Before bisulfite treatment, genomic DNA (1 µg) was digested with PstI (10 U). Bisulfite modification was performed using a CpGenome DNA Modification kit (Serologicals Corporation, Norcross, GA). After bisulfite treatment, genomic DNA was amplified using primers specific for methylated and unmethylated versions of the exon 1A region (GenBank accession no. AF246983) (Table 3). We performed the sequencing of amplicons by each methylated- and unmethylated-specific primer pair [1A(M), 123 bp; 1A(U), 111 bp) by using TA cloning.
Southern blot analysis
For methylation-status analysis, 10 µg genomic DNA was digested with a combination of methylation-sensitive and methylation-insensitive restriction enzymes (New England Biolabs, Beverly, MA), fractionated on 1% agarose gels, and blotted onto nylon membranes. Prehybridization, hybridization, and probe labeling were performed using AlkPhos Direct (Amersham Pharmacia Biotech, Tokyo, Japan), as we previously reported (7). The probes comprised the PCR products, using the following sets of forward and reverse primers: 5'-GCTAGCTTGCCGCTTGCTCCTT-3' and 5'-CTTCGCAACTTGAGAGCGTGCAG-3' for the NESP55 region (1103 bp); 5'-CACTGCCCCAGCCGCTTCT-3' and 5'-AGCCCCTGCCTGTCCAGCTT-3' for the XL region (885 bp).
X-chromosome inactivation analysis
We analyzed the DNA from the patient’s peripheral blood leukocytes, urinary sediment, and renal tissue. The DNA from the paraffin-embedded kidney sample was isolated, using a PS isolation kit (Wako, Osaka, Japan).
The X-inactivation pattern was determined by PCR analysis of a polymorphic CAG repeat in the first exon of the androgen receptor (AR) gene (8). After digestion with the methylation-sensitive enzymes HpaII and HhaI, a PCR product was obtained from the inactive X-chromosome only. The 5'-end of the forward primer was modified with fluorescein (6'-NED). Two microliters of undigested and digested samples were amplified in a reaction volume of 25 µl for 30 cycles using specific primers (Table 3). PCR products from undigested and digested DNA were separated on an ABI373 automated sequencer and analyzed by GeneScan software (Applied Biosystems Japan, Tokyo, Japan).
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Results
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Genetic analysis of the GNAS gene
No mutations were found in exons 1–13 or in any exon-intron boundary of the GNAS gene. However, the patient was a heterozygote for both the exon 5 single-nucleotide polymorphism (5) and the exon 1A pentanucleotide repeat polymorphism (5) (Fig. 3). Figure 4 shows a frame format of the RT-PCR primers. Allele-specific expression analysis of exon 1A mRNA transcripts revealed that exon 1A mRNA, which is normally monoallelically expressed, was biallelically expressed in this patient. Twenty-eight of the 61 clones we studied were T alleles, and 33 were C alleles (data not shown). Thus, an imprinting defect was thought to be the cause of her PTH resistance (4, 5).
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FIG. 3. Direct genomic sequencing analysis of GNAS exon 1A in the patient’s leukocyte DNA. She is heterozygous for the exon 1A pentanucleotide repeat polymorphism. Each repeat of the pentanucleotide GGCGC is indicated with brackets.
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FIG. 4. Genomic structure of the GNAS gene showing RT-PCR primers (arrows) and the polymorphic FokI site in exon 5 (arrowhead) (C or T allele). FokI recognizes the C allele but not the T allele.
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To examine exon 1A methylation status, we performed MSP and bisulfite genomic sequencing. Treatment of genomic DNA with sodium bisulfite followed by alkaline treatment converts unmethylated cytosine to uracil, while leaving methylated cytosine residues intact. Sequence variants at exon 1A can be analyzed subsequently by PCR amplification with primers designed to anneal with bisulfite-converted DNA. Compared with a normal subject, the 1A(M) amplicons of the patient were not visualized on a 2% agarose gel staining etidium bromide, whereas 1A(U) amplicons were obtained from both a normal subject and the patient (Fig. 5). Next, individual 1A(M) and 1A(U) amplicons were subcloned and sequenced. In a normal subject, who is informative for the exon 1A polymorphism (data not shown), 3-repeat pentanucleotide alleles were 1A(M) amplicons, whereas 2-repeat pentanucleotide alleles were 1A(U) amplicons (Fig. 6A). 1A(U) PCR products of the patient were fully unmethylated fragments containing 3-repeat and 2-repeat GGCGC (Fig. 6B). These results indicate that her PTH resistance might be due to a GNAS imprinting defect, as previously reported (4, 6).
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FIG. 5. MSP analysis of GNAS exon 1A in leukocyte DNA. The 1A(M) amplicons of the patient were not visualized, whereas 1A(U) amplicons of both a normal subject and the patient were successfully obtained. 1A(M), PCR products using exon 1A(M) primers; 1A(U), PCR products using exon 1A(U) primers.
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FIG. 6. Bisulfite genomic sequencing analysis of GNAS exon 1A in leukocyte DNA. Each repeat of the pentanucleotide GGCGC is indicated with brackets. A, Results of bisulfite genomic sequencing of 1A(M) and 1A(U) amplicons of a normal subject heterozygous for the exon 1A pentanucleotide repeat polymorphism. Eight clones of 1A(M) and seven clones of 1A(U) amplicons were sequenced. All 1A(M) clones are fully methylated fragments containing 3-repeat GGCGC, whereas all 1A(U) clones are fully unmethylated fragments containing 2-repeat GGCGC. B, Results of bisulfite genomic sequencing of 1A(U) amplicons of the patient. A total of 16 clones of 1A(U) amplicons were sequenced. Both 3-repeat (nine clones) and 2-repeat alleles (seven clones) are completely unmethylated. These results show a methylation defect at exon 1A in the patient.
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It has been reported that patents with PHPIB have an abnormal methylation pattern at exon 1A and sometimes also even at exons NESP55 and XL (4, 5). Southern blot analysis using probes specific for the NESP and XL regions revealed abnormalities in her genomic DNA. She showed a gain of methylation in exon NESP55 and a loss of methylation in exon XL (Fig. 7).
X-inactivation analysis
The patient was heterozygous for the CAG repeat [(CAG)17/(CAG)23] in the AR gene and therefore was informative in the X-inactivation assay. Methylation of HpaII and HhaI sites in close proximity to this CAG repeat correlates with X-chromosome inactivation. After digestion, PCR amplification yielded only a single peak, whereas two peaks were obtained from prior digestion. These results showed completely SXI in the DNA from her leukocytes, urinary sediment, and renal tissue (Fig. 8).
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FIG. 8. X-inactivation analysis of an androgen receptor CAG repeat in leukocytes, urinary sediment, and kidney DNA. No peak corresponding to the (CAG)23 allele was detected in digested DNA, indicating completely SXI.
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Discussion
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We encountered a young, female patient with juvenile hypertension and increased renin activity. She showed exceptional features, including a round face, short stature, obesity, and mental deficits (IQ, 49), partially resembling an AHO phenotype. Despite close examination, we could not elucidate the cause of her renin-mediated hypertension. We did, however, suspect that she suffered from PHPIA, owing to her AHO-like features. After detailed clinical examination, we found her to be PTH resistant, without additional resistance to TSH, LH, and FSH.
We performed mutational analysis of her GNAS gene because of the well known association between PHP and mutations in this gene. PHPIB is generally associated with a GNAS imprinting defect (4, 5). Genetic analysis of the GNAS gene revealed an imprinting defect at exon 1A, which could explain her PTH resistance (4, 5) but not her AHO-like phenotype or her renin-dependent hypertension.
To better understand this complex phenotype, we focused our attention on her mental retardation. Many types of mental retardation are linked to the X-chromosome and have a common feature of SXI (8). We, therefore, performed X-inactivation analysis and found complete skewing of X-inactivation in the DNA from her leukocytes, urinary sediment, and a kidney biopsy specimen.
Approximately 150 distinct types of mental retardation are mapped to the X-chromosome and several genes responsible for X-linked mental retardation (XLMR) have been identified (9, 10, 11, 12). Genes on the X-chromosome are considered to cause a substantial proportion of undiagnosed mental retardation (13). Skewing of the X-inactivation pattern is known to occur when there is a lethal mutation on one X-chromosome (2, 3). The detection of completely SXI in multiple tissues strongly suggests that this patient has XLMR.
Intellectual disability is often associated with other neurological symptoms, metabolic disorders, and malformation syndromes (9, 10, 11, 12). There are many types of syndromic XLMR, and an imprinting abnormality is reported to cause manifestations in some types of syndromic XLMR, such as X-linked -thalassemia mental retardation syndrome and Rett syndrome. In these disorders, the mutated gene on the X-chromosome associated with the imprinting system is thought to result in defects in chromatin structure and transcriptional repression of some genes (14, 15). A coincidence of AHO-like phenotype, including mental deficits, with completely SXI and PHPIB indicates a gene mutation on the X-chromosome linked to a methylation defect and epigenetic regulation.
Hypertension is a common feature of PHPIA and PHPIB, strongly linked to obesity. Alterations in the renin-angiotensin axis have been described in PHP (16). Both basal and stimulated levels of PRA and PAC were reduced in hypertensive patients with PHP (16), indicating that the renin-angiotensin axis does not play a major role in the pathogenesis of hypertension in PHP. Thus, the cause of her hypertension distinctly differs from that of ordinary PHPIB patients.
Hyperreninemic hypertension can result from malignant hypertension, renovascular hypertension, renal parenchymal disease, pheochromocytoma, or a renin-secreting tumor. This patient’s hyperrenism did not correspond to any of these causes, despite close examination. We did find completely SXI in her renal tissue and renal resistance to PTH associated with a GNAS imprinting defect, indicating a possible genetic defect expressed in her kidneys. Thus, her renin-mediated hypertension may also result from an imprinting defect of some gene.
Here, we describe a mentally deficient young female with completely SXI in multiple tissues and renal resistance to PTH associated with a GNAS imprinting defect. Our investigation suggests that this may be an unprecedented type of syndromic XLMR with AHO-like phenotype, PHPIB, and renin-dependent hypertension.
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Acknowledgments
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We thank Drs. Kyoko Miyagi and Ichiro Kon-i for performing the renal analysis and Junko Kubo for preparing the renal biopsy specimen.
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Footnotes
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Abbreviations: AHO, Albright’s hereditary osteodystrophy; AR, androgen receptor; CT, computed tomography; MSP, methylation-specific PCR; PAC, plasma aldosterone concentration; PHP, pseudohypoparathyroidism; PHPIA, PHP type IA; PHPIB, PHP type IB; PRA, plasma-renin activity; SXI, skewed X-inactivation; XLMR, X-linked mental retardation.
Received October 1, 2002.
Accepted March 25, 2003.
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References
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- Lyon MF 1961 Gene action in the X-chromosome of the mouse (Mus musculus L.). Nature 190:372–373[CrossRef][Medline]
- Belmont JW 1996 Genetic control of X inactivation and processes leading to X-inactivation skewing. Am J Hum Genet 58:1101–1108[Medline]
- Puck JM, Willard HF 1998 X inactivation in females with X-linked disease. New Engl J Med 338:325–328[Free Full Text]
- Weinstein LS, Yu S, Warner DR, Liu J 2001 Endocrine manifestations of stimulatory G protein -subunit mutations and the role of genomic imprinting. Endocr Rev 22:675–705[Abstract/Free Full Text]
- Liu J, Litman D, Rosenberg MJ, Yu S, Biesecker LG, Weinstein LS 2000 A GNAS1 imprinting defect in pseudohypoparathyroidism type IB. J Clin Invest 106:1167–1174[Medline]
- Fukami T, Fujita T, Yoshimoto Y, Fukase M, Imai Y, Sakaguchi K, Ogata E, Furukawa Y, Suzuki H, Takebe K, Yoshida S, Kitagawa T, Igarashi Y, Yamada T, Takeda R, Tomita A, Imura H, Kumahara Y, Harada Y, Ofuji T, Ibayashi H, Nagataki S, Sato T, Fujita T 1984 Urinary phosphate and cyclic adenosine monophosphate response to intravenous administration of synthetic human parathyroid hormone-(1–34) in idiopathic hypoparathyroidism, pseudohypoparathyroidism, pseudopseudohypoparathyroidism and normal subjects. Nippon Naibunpi Gakkai Zasshi 60:159–170[Medline]
- Demura M, Takeda Y, Yoneda T, Furukawa K, Usukura M, Itoh Y, Mabuchi H 2002 Two novel types of contiguous gene deletion of the AVPR2 and ARHGAP4 genes in unrelated Japanese kindreds with nephrogenic diabetes insipidus. Hum Mutat 19:23–29[CrossRef][Medline]
- Plenge RM, Stevenson RA, Lubs HA, Schwartz CE, Willard HF 2002 Skewed X-chromosome inactivation is a common feature of X-linked mental retardation disorders. Am J Hum Genet 71:168–173[CrossRef][Medline]
- Cabezas DA, Arena JF, Stevenson RE, Schwartz CE, Goldberg S, Morales A, Lubs 1999 HA XLMR database. Am J Hum Genet 85:202–205
- Stevenson RE, Schwartz CE, Schroer RJ 1999 X-Linked mental retardation. New York and Oxford, UK: Oxford University Press
- Hamel BC, Chiurazzi P, Lubs HA 2000 Syndromic XLMR genes (MRXS): update 2000. Am J Med Genet 94:361–363[Medline]
- Chelly J, Mandel JL 2001 Monogenic causes of X-linked mental retardation. Nat Rev Genet 2:669–680[Medline]
- Partington M, Mowat D, Einfeld S, Tonge B, Turner G 2000 Genes on the X chromosome are important in undiagnosed mental retardation. Am J Med Genet 92:57–61[CrossRef][Medline]
- Gibbons RJ, McDowell TL, Raman S, O’Rourke DM, Garrick D, Ayyub H, Higgs DR 2000 Mutations in ATRX, encoding a SWI/SNF-like protein, cause diverse changes in the pattern of DNA methylation. Nat Genet 24:368–371[CrossRef][Medline]
- Amir RE, Van den Veyver IB, Wan M, Tran CQ, Francke U, Zoghbi HY 1999 Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein. Nat Genet 23:185–188[CrossRef][Medline]
- Brickman AS, Stern N, Sowers JR 1988 Hypertension in pseudohypoparathyroidism type I. Am J Med 85:785–792[Medline]
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Abstract
Introduction
, All of the different first exons; 
, normal parent-specific transcription; dashed arrow, paternal exon 1, probably imprinted in some tissues; brackets, normal methylated sites of the parental alleles; thick lines, the probes used in Southern blot analysis: NESP55 (nucleotides 255-1357; GenBank accession no.