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. 2011 Oct 7;89(4):551-63.
doi: 10.1016/j.ajhg.2011.09.011.

Assessment of 2q23.1 microdeletion syndrome implicates MBD5 as a single causal locus of intellectual disability, epilepsy, and autism spectrum disorder

Michael E Talkowski  1 , Sureni V Mullegama, Jill A Rosenfeld, Bregje W M van Bon, Yiping Shen, Elena A Repnikova, Julie Gastier-Foster, Devon Lamb Thrush, Sekar Kathiresan, Douglas M Ruderfer, Colby Chiang, Carrie Hanscom, Carl Ernst, Amelia M Lindgren, Cynthia C Morton, Yu An, Caroline Astbury, Louise A Brueton, Klaske D Lichtenbelt, Lesley C Ades, Marco Fichera, Corrado Romano, Jeffrey W Innis, Charles A Williams, Dennis Bartholomew, Margot I Van Allen, Aditi Parikh, Lilei Zhang, Bai-Lin Wu, Robert E Pyatt, Stuart Schwartz, Lisa G Shaffer, Bert B A de Vries, James F Gusella, Sarah H Elsea
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"VSports在线直播" Assessment of 2q23.1 microdeletion syndrome implicates MBD5 as a single causal locus of intellectual disability, epilepsy, and autism spectrum disorder

Michael E Talkowski et al. Am J Hum Genet. .

Abstract

Persons with neurodevelopmental disorders or autism spectrum disorder (ASD) often harbor chromosomal microdeletions, yet the individual genetic contributors within these regions have not been systematically evaluated. We established a consortium of clinical diagnostic and research laboratories to accumulate a large cohort with genetic alterations of chromosomal region 2q23. 1 and acquired 65 subjects with microdeletion or translocation. We sequenced translocation breakpoints; aligned microdeletions to determine the critical region; assessed effects on mRNA expression; and examined medical records, photos, and clinical evaluations. We identified a single gene, methyl-CpG-binding domain 5 (MBD5), as the only locus that defined the critical region. Partial or complete deletion of MBD5 was associated with haploinsufficiency of mRNA expression, intellectual disability, epilepsy, and autistic features. Fourteen alterations, including partial deletions of noncoding regions not typically captured or considered pathogenic by current diagnostic screening, disrupted MBD5 alone. Expression profiles and clinical characteristics were largely indistinguishable between MBD5-specific alteration and deletion of the entire 2q23. 1 interval. No copy-number alterations of MBD5 were observed in 7878 controls, suggesting MBD5 alterations are highly penetrant. We surveyed MBD5 coding variations among 747 ASD subjects compared to 2043 non-ASD subjects analyzed by whole-exome sequencing and detected an association with a highly conserved methyl-CpG-binding domain missense variant, p. 79Gly>Glu (c VSports手机版. 236G>A) (p = 0. 012). These results suggest that genetic alterations of MBD5 cause features of 2q23. 1 microdeletion syndrome and that this epigenetic regulator significantly contributes to ASD risk, warranting further consideration in research and clinical diagnostic screening and highlighting the importance of chromatin remodeling in the etiology of these complex disorders. .

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Figure 1
Figure 1
Delineation of the 2q23.1 Critical Region Schematic representation of MBD5-containing deletions and translocation breakpoints in this report and those previously reported in the literature, arranged from largest to smallest. Boxes represent the minimum size of the deletions, and the horizontal lines extend through gaps in coverage to show the maximum deletion sizes. Green boxes represent individuals with MBD5 expression studies reported here. Single asterisks indicate cases known to be de novo; a double asterisk indicates a single inherited case in the cohort. Inheritance regarding all other cases is unknown. Genes within the region are represented by blue boxes, and the shaded region shows the location of MBD5.
Figure 2
Figure 2
Deletions and Translocations Disrupting MBD5 (Top) Schematic representation of intragenic and partial deletions of MBD5. MBD5 genomic organization and mRNA (RefSeq Accession: NM_018328) are provided, including the large noncoding region (in green) between exon 1 and the coding sequence start site (in blue). Above the gene are the 18 microdeletions that partially and/or exclusively disrupt MBD5. These subjects had similar phenotypic features to individuals with deletions of the full 2q23.1 region (Table 1). Green bars represent those cases with expression data shown in Figure 4. Single asterisks indicate cases known to be de novo; the double asterisk indicates a single inherited case in the cohort. Inheritance regarding all other cases is unknown. (Bottom) Translocation breakpoints in MBD5. Below the gene are paired-end sequencing data from two translocations found to disrupt MBD5. The arrows represent the orientation of sequence reads (inward facing for CapBP, outward facing for jumping libraries). The breakpoint on chromosome 2 in SMS373 was localized to the MBD5 noncoding region but determined to be an unbalanced rearrangement with derivative breakpoints separated by 193 kb on chromosome 2 and 106 kb on chromosome 10. DGAP142 yielded read pairs that localized the junction fragment to the same noncoding region with the loss of a single base at the chromosome 22 breakpoint in a region without annotated genes or functional sequences. Breakpoint sequences are given below the reads. The blue sequence represents the chromosome 2 breakpoint; the red sequence represents the chromosomal partner sequence, and the sequence at the breakpoint that does not map to either chromosome partner is inserted in gray. Breakpoints for both derivatives resulting in the 193 kb deletion of chromosome 2 are shown for SMS373. The second derivative of DGAP142 was balanced and identical to the reference.
Figure 3
Figure 3
Clinical Features of Patients with Haploinsufficiency of MBD5 (A–D) The individuals presented have different 2q23.1 deletions (Figure 1). (A) SMS375, age 19 months. Note the microcephaly (45.8 cm, < 3rd percentile), broad forehead, bulbous nose, simple protruding ear lobes, and thin upper lip. (B) SMS373, age 2. Note the broad forehead, midface hypoplasia, high and broad nasal root, bulbous nose, fleshy ear lobes with bilateral Darwinian tubercle, and thin upper lip. (C) SMS367, age 7. Note low anterior hairline, midface retrusion (hypoplasia), large pronounced nose, and prominent columella. Note the space between the incisors. (D) SMS368, age 20. Note the bitemporal narrowing, synophrys, large pronounced nose, prominent ears, prominent columella, protruding upper teeth, and short neck. (E) Hands of SMS373. Note the small plump hands, brachydactyly, and fifth finger clinodactyly. (F) Feet of SMS373. Note the small feet and sandal gap between first and second toes. (G) Feet of SMS368 illustrating small size and slight sandal gap between first and second toes. (H) Hands of SMS368. Note the small hands with tapered fingers and the fifth finger clinodactyly.
Figure 4
Figure 4
Reduced MBD5 Expression with MBD5 Deletions or Disruptions Quantitative RT-PCR mRNA expression analysis of MBD5 is shown in lymphoblastoid cell lines or peripheral blood lymphocytes from individuals with MBD5 deletions (partial or complete) or disruptions of MBD5 and nine unaffected (no MBD5 deletion) subjects that were used as normal controls. Results were normalized to GAPDH expression. Relative expression values are based on the ΔΔCt value. Expression of all controls was normalized to one. Each bar represents mean (±standard error of the mean) of values from three to ten independent experiments. The error bars are present for each sample, but in some cases the error bars are too small to be seen. The data show a normal range of expression, 0.94- to 1.23-fold MBD5 expression, in lymphocytes (BC1-2) and lymphoblastoid cell lines (LCL1-7). Samples from cases described herein show 22%–55% expression of MBD5 (p < 0.0001 for all cases). aSMS185 and SMS361 were previously reported.
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