Eur J Pediatr (2005) 164: 154–157 DOI 10.1007/s00431-004-1583-x
O R I GI N A L P A P E R
Konrad Oexle Æ Barbara Thamm-Mu¨cke Thomas Mayer Æ Sigrid Tinschert
Macrocephalic mental retardation associated with a novel C-terminal MECP2 frameshift deletion
Received: 1 September 2004 / Revised: 19 October 2004 / Accepted: 20 October 2004 / Published online: 19 November 2004 Ó Springer-Verlag 2004
Abstract We report a novel C-terminal MECP2 frameshift deletion (1135_1142delCCCGTG CC) in a 19-year-old woman with mental retardation and epilepsy. Preservation of language capabilities, purposeful hand use and sufficient locomotion implied an atypical variant of Rett syndrome (OMIM 312750). Occipitofrontal head circumference was large at birth (36 cm; SDS 1.7) and increased until adulthood (58.5 cm; SDS 2.3). Conclusion: Our observation indicates that head size and head growth are of limited reliability in the diagnosis of MECP2-associated phenotypes. Keywords Atypical Rett syndrome Æ Cephalometry Æ Frameshift mutation Æ MECP2 gene Æ Mental retardation Abbreviations MeCP2: methyl-CpG-binding protein 2 Æ RTT: Rett syndrome
Introduction Heterozygous mutations of X-linked MECP2, the gene of methyl-CpG-binding protein 2, cause classical Rett syndrome (RTT) [1], a severe neuro-developmental disorder in girls characterised by the loss of acquired skills
K. Oexle (&) Æ S. Tinschert Institut fu¨r Klinische Genetik, Medizinische Fakulta¨t Carl Gustav Carus, Technische Universita¨t Dresden, Fetscherstrasse 74, 01307 Dresden, Germany E-mail:
[email protected] Tel.: +49-351-4585199 Fax: +49-351-4584316 B. Thamm-Mu¨cke Labor Dr. Reising-Ackermann und Partner, Leipzig, Germany T. Mayer Epilepsiezentrum Kleinwachau, Liegau-Augustusbad, Germany
such as speech and purposeful hand use after a relatively normal development during the first months of life, subnormal head growth, autistic behaviour with stereotypic hand movements, impaired locomotion, autonomous dysfunction, and seizures. MECP2 mutations are found in six to nine out of ten patients with typical RTT, but also in about 50% of the patients with atypical RTT, and even in 5% of girls with poorly specific mental retardation and few RTT-like features [6, 14]. RTT was believed to be an X-linked dominant condition lethal in hemizygous males; however, RTT encephalopathy may occur in newborn boys [12]. Furthermore, MECP2 mutations can be found in a syndrome called ‘‘PPM-X’’ (psychosis, pyramidal signs, macro-orchidism, X-linked) [7] and in a small fraction (0.2%) [16] of males with non-specific X-linked mental retardation. The gene product methyl-CpG-binding protein 2 (MeCP2) consists of a methyl-binding domain, a transcription repression domain, and a C-terminal domain. Recently, a second MeCP2 isoform was identified that has an additional N-terminal signal-like peptide and shows a ten times higher expression level in brain tissue [8]. The genotype-phenotype relationship of MECP2 mutations is variable and controversial [6, 9, 10, 14].
Case report A 19-year-old German woman (Fig. 1) presented with mental retardation (IQ between 35 and 50). Her standing height was 174 cm (SDS 1.5), her body weight was 82 kg (body mass index 27), and her occipito-frontal head circumference (OFC) was 58.5 cm (SDS = (58.5 – 54.8)/1.6 = 2.3); note that on the basis of North American reference data [11], SDS = (58.5 – 54.55)/1.33 = 3.0). Her speech production was reduced to rare oneor two-word sentences whereas speech perception was relatively good. She showed signs of ataxia when standing on one leg and was unable to ride a bicycle. Hand use was adequate and comparatively skillful in
155
15q12, methylation-specific PCR within exon 1 of the SNPRN gene, and PCR-amplification of MECP2 exons [1,13] were performed according to established protocols. For sequencing, the ABI 3100 system and the BigDye Terminator Cycle Sequencing Kit (Applied Biosystems) were used. The detected mutation was described according to the Human Gene Mutation Database (HGMD), Cardiff, UK (http://archive.uwcm.ac.uk/ uwcm/mg/cdna/3851454.txt) .
Results
Fig. 1 The patient at presentation showing macrocephaly without dysmorphic features
Karyotype (46, XX) and 5’-UTR CGG-repeat lengths of the FraX syndrome gene FMR1 were normal. The Prader-Willi/Angelman locus at 15q12 showed no evidence of deletion, imprinting defect, or uniparental disomy. In exon 4 of the MECP2 gene, a heterozygous mutation 1135_1142delCCCGTGCC was detected (Fig. 2) involving the C-terminal codons 379, 380, and 381. Deletion of these eight nucleotides caused a frameshift and a stop of translation at position 1173 of the wildtype sequence. Identical sequence alterations
carving of wooden animals, for instance. Episodically, however, repetitive hand movements occurred. Except for sleep disturbances, there was no evidence of autonomous dysregulation. Focal neurological signs were not observed. Dermatological, gynaecological and orthopaedic examinations gave normal results. Acylcarnitines in blood and urinary concentrations of ketones, amino acids, beta-ketoacids, glycosaminoglycans, and oligosaccharides were normal. Birth length and weight of the proposita were normal (50 cm and 3.22 kg, respectively). OFC at birth was 36 cm (SDS 1.7). Mental and motor development slowed down in second half of the 1st year. At the age of 24 months she walked freely and communicated in short sentences. Thereafter, her speech deteriorated to the current level. At the age of 12 years, signs of ataxia were described. Startle-induced myocloni were observed in childhood, beginning at the age of 2 years. In puberty, occasional generalised tonic-clonic seizures occurred. The family history was unremarkable. Body lengths and OFCs (SDSmother 0.4, SDSfather -1.1) of the firstgrade relatives were normal.
Methods Body height and OFC were compared to East German reference data [3] if not indicated otherwise. SDS were calculated as the difference from the mean divided by the standard deviation. Karyotyping, 5’-UTR CGG-repeat length determination of the FMR1 gene by fluorescence-PCR, automated fragment analysis, and Southern blotting, FISH of
Fig. 2 Mutation 1135_1142delCCCGTGCC in exon 4 of the MECP2 gene. Top: mutated sequence in the patient. Bottom:wildtype sequence in the patient’s mother. Beginning with the C at position 1135, the sequence of the patient’s wildtype allele is overlapped by the sequence of her deleted allele, i.e., by the sequence that starts with the A at position 1143 of the wildtype. (A coloured version of the sequencing results may be requested from the authors.)
156
would be caused by the deletions 1134_1141delCCCCGTGC and 1133_1140delCCCCCGTG. The choice of one of the three equivalent alternatives was arbitrary. The MECP2 mutation was not found in the patient’s unaffected sister and mother (Fig. 2). The father was not available for genetic testing.
observation of a woman with a relatively large head size at birth (96th percentile) and a relative increase until adulthood (99th percentile) reminds one of the remark of Hagberg et al. [4] that head growth should neither be regarded as a necessary diagnostic criterion for typical RTT, nor as a valid one for forme fruste variants.
Discussion
Acknowledgements We thank Prof. Dr. Evelin Schro¨ck and Dr. Walter Werner for helpful discussions.
The patient presented here had rather non-specific neurological features such as mental handicap and epilepsy. Deterioration of language skills during childhood was compatible with RTT. However, at the age of presentation (19 years), preserved speech, comparatively skillful hand use, sufficient locomotion, relatively large body size, and macrocephaly excluded a diagnosis of the classical form of RTT. We identified an 1135_1142delCCCGTGCC MECP2 frameshift deletion that truncated the C-terminus 11 new codons downstream of the last undeleted codon. The RettBASE data collection (http://mecp2.chw.edu.au/) contains an unpublished entry that reports a frameshift deletion 1136_1142delCCGTGCC inducing a stop of translation 28 new codons downstream of the last undeleted codon. However, detailed clinical information on that case is lacking. According to Cheadle et al. [2], truncating MECP2 mutations located upstream of the transcription repression domain cause severe RTT phenotypes. Renieri et al. [10] even conjectured that atypical, that is, milder phenotypes with preserved speech relate only to missense mutations or to truncating C-terminal mutations whereas classical RTT may be associated with any of the spectrum of MECP2 mutations. However, while our report is in accordance with this conjecture, others sporadically observed preserved speech variants in cases of truncating mutations within the transcription repression domain that is upstream of the C-terminus [2, 6, 15]. Indeed, the genotype-phenotype relationship of MECP2 mutations appears to be complex. A simple relationship between phenotype and X-inactivation pattern does not seem to prevail [9]. Besides mutation type, mutated domain, and X-inactivation pattern, modifying genes [10] and MeCP2 isoforms [8] might be relevant. The confounding interaction of these factors may be such that some investigators cannot recognise any genotype-phenotype relationship in their patient group [6]. On average, head size and head growth are subnormal in MECP2-associated phenotypes [5]. Weaving et al. [14] observed that head circumference tended to be larger in patients with truncating mutations and/or mutations that did not affect the methyl-binding domain. Our report complies with this observation. Kammoun et al. [6] stated that acquired low head circumference is one of four criteria whose concurrence is highly predictive (90%) of a MECP2 mutation. Thereby, high diagnostic relevance was attributed to head size. However, our
References 1. 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 2. Nat Genet 23: 185–188 2. Cheadle JP, Gill H, Fleming N, Maynard J, Kerr A, Leonard H, Krawczak M, Cooper DN, Lynch S, Thomas N, Hughes H, Hulten M, Ravine D, Sampson JR, Clarke A (2000) Long-read sequence analysis of the MECP2 gene in Rett syndrome patients: correlation of disease severity with mutation type and location. Hum Mol Genet 9: 1119–1129 3. Flu¨gel B, Greil H, Sommer K (1986) Anthropologischer Atlas. Verlag Tribu¨ne, Berlin 4. Hagberg G, Stenbom Y, Engerstrom IW (2001) Head growth in Rett syndrome. Brain Dev 23[Suppl 1]: S227–S229 5. Huppke P, Held M, Laccone F, Hanefeld F (2003) The spectrum of phenotypes in females with Rett syndrome. Brain Dev 25: 346–351 6. Kammoun F, de Roux N, Boespflug-Tanguy O, Vallee L, Seng R, Tardieu M, Landrieu P (2004) Screening of MECP2 coding sequence in patients with phenotypes of decreasing likelihood for Rett syndrome: a cohort of 171 cases. J Med Genet 41: e85 7. Klauck SM, Lindsay S, Beyer KS, Splitt M, Burn J, Poustka A (2002) A mutation hot spot for nonspecific X-linked mental retardation in the MECP2 gene causes the PPM-X syndrome. Am J Hum Genet 70: 1034–1037 8. Mnatzakanian GN, Lohi H, Munteanu I, Alfred SE, Yamada T, MacLeod PJ, Jones JR, Scherer SW, Schanen NC, Friez MJ, Vincent JB, Minassian BA (2004) A previously unidentified MECP2 open reading frame defines a new protein isoform relevant to Rett syndrome. Nat Genet 36: 339–341 9. Nielsen JB, Henriksen KF, Hansen C, Silahtaroglu A, Schwartz M, Tommerup N (2001) MECP2 mutations in Danish patients with Rett syndrome: high frequency of mutations but no consistent correlations with clinical severity or with the X chromosome inactivation pattern. Eur J Hum Genet 9: 178– 184 10. Renieri A, Meloni I, Longo I, Ariani F, Wari F, Pescucci C, Cambi F (2003) Rett syndrome: the complex nature of a monogenic disease. J Mol Med 81: 346–354 11. Roche AF, Mukherjee D, Guo S, Moore WM (1987) Head circumference reference data: birth to 18 years. Pediatrics 79: 706–712 12. Schanen C, Francke U (1998) A severely affected male born into a Rett syndrome kindred supports X-linked inheritance and allows extension of the exclusion map. Am J Hum Genet 63: 267–269 13. Wan M, Lee SS, Zhang X, Houwink-Manville I, Song HR, Amir RE, Budden S, Naidu S, Pereira JL, Lo IF, Zoghbi HY, Schanen NC, Francke U (1999) Rett syndrome and beyond: recurrent spontaneous and familial MECP2 mutations at CpG hotspots. Am J Hum Genet 65: 1520–1529 14. Weaving LS, Williamson SL, Bennetts B, Davis M, Ellaway CJ, Leonard H, Thong MK, Delatycki M, Thompson EM, Laing N, Christodoulou J (2003) Effects of MECP2 mutation type, location and X-inactivation in modulating Rett syndrome phenotype. Am J Med Genet 118A: 103–114
157 15. Yamashita Y, Kondo I, Fukuda T, Morishima R, Kusaga A, Iwanaga R, Matsuishi T (2001) Mutation analysis of the methyl-CpG-binding protein 2 gene (MECP2) in Rett patients with preserved speech. Brain Dev 23[Suppl 1]: S157–S160
16. Yntema HG, Kleefstra T, Oudakker AR, Romein T, de Vries BB, Nillesen W, Sistermans EA, Brunner HG, Hamel BC, van Bokhoven H (2002) Low frequency of MECP2 mutations in mentally retarded males. Eur J Hum Genet 10: 487–490
