Open Access
Open Peer Review

This article has Open Peer Review reports available.

How does Open Peer Review work?

Novel PRRT2 mutation in an African-American family with paroxysmal kinesigenic dyskinesia

  • Peter Hedera1,
  • Jianfeng Xiao2,
  • Andreas Puschmann3,
  • Dragana Momčilović4,
  • Steve W Wu5 and
  • Mark S LeDoux2Email author
Contributed equally
BMC Neurology201212:93

DOI: 10.1186/1471-2377-12-93

Received: 26 May 2012

Accepted: 16 September 2012

Published: 18 September 2012

Abstract

Background

Recently, heterozygous mutations in PRRT2 (Chr 16p11.2) have been identified in Han Chinese, Japanese and Caucasians with paroxysmal kinesigenic dyskinesia. In previous work, a paroxysmal kinesigenic dyskinesia locus was mapped to Chr 16p11.2 - q11.2 in a multiplex African-American family.

Methods

Sanger sequencing was used to analyze all four PRRT2 exons for sequence variants in 13 probands (9 Caucasian, 1 Caucasian-Thai, 1 Vietnamese and 2 African-American) with some form of paroxysmal dyskinesia.

Results

One patient of mixed Caucasian-Thai background and one African-American family harbored the previously described hotspot mutation in PRRT2 (c.649dupC, p.R217Pfs*8). Another African-American family was found to have a novel mutation (c.776dupG, p.E260*). Both of these variants are likely to cause loss-of-function via nonsense-mediated decay of mutant PRRT2 transcripts. All affected individuals had classic paroxysmal kinesigenic dyskinesia phenotypes.

Conclusions

Heterozygous PRRT2 gene mutations also cause paroxysmal kinesigenic dyskinesia in African-Americans. The c.649dupC hotspot mutation in PRRT2 is common across racial groups.

Keywords

PKD PRRT2 African-American ICCA Hotspot mutation

Background

Paroxysmal kinesigenic dyskinesia (PKD, OMIM 128000), also known as episodic kinesigenic dyskinesia (EKD1) and paroxysmal kinesigenic choreoathetosis (PKC), is a rare autosomal dominant neurological disorder characterized by recurrent, brief attacks of involuntary movement usually triggered by sudden voluntary movement [1, 2]. These attacks usually begin in childhood or early adulthood and may include various combinations of dystonia, chorea, and athetosis affecting the face, trunk, arms and legs. Oftentimes, PKD improves with age and most patients show a favorable response to anticonvulsant medications, particularly carbamazepine or phenytoin [1, 2]. Recently, mutations in PRRT2 (Chr 16p11.2) have been causally associated with both familial and sporadic cases of PKD, infantile convulsions and choreoathetosis (ICCA), benign familial infantile epilepsy (BFIE), paroxysmal exercise-induced dyskinesia (PED), and paroxysmal non-kinesigenic dyskinesia-like (PNKD-like) syndromes in Han Chinese, Japanese and Caucasians [311].

PKD is clinically and genetically heterogeneous, and, in at least one British pedigree, does not map to Chr 16 [12]. Work to date suggests that fewer than 50% of patients with primary PKD harbor mutations in PRRT2 [6, 8]. To expand the genotypic spectrum of PRRT2 mutations and examine the role of PRRT2 in other racial groups, we report the clinical and genetic data for 13 probands with paroxysmal dyskinesias including 1 Vietnamese, 1 mixed Caucasian-Thai and 2 African-Americans.

Methods

All human studies were performed in accordance with institutional review board guidelines at each participating institution, the Helsinki Declaration, and written informed consent for genetic studies and publication of clinical data was obtained from all subjects or, where participants were children, their parents. All genetic and phenotypic analyses and publication of the results were approved by the University of Tennessee Health Science Center Institutional Review Board (#01-07346-XP). Subjects were acquired from outpatient clinics at participating institutions. Clinical diagnoses were made by means of history and examination by one or more board-certified neurologists at each institution. Clinical and genetic details for 13 probands are presented Table 1.
Table 1

Clinical details and genetic results for subjects with paroxysmal dyskinesias

Subject (Diagnosis)

PRRT2 Mutation

Age/Gender

Race

Age at onset(y)

Family history

Attack frequency

Attack duration

Triggers

Involuntary movements

Anatomical distribution

Response to anticonvulsants

Family A, II-1 (PKD)

NA

NA/M

African-American

10y

Yes

< 100/day

10-20 sec

SM

D, C

A, L

carbamazepine(+), phenytoin (+)

Family A, III-1 (PKD)

NA

28y/F

African-American

12y

Yes

20-30/day

10-40 sec

SM

D, C

F, A, L

phenytoin (+)

Family A, III-2 (PKD)

NA

25y/F

African-American

10y

Yes

50-75/day

10-15 sec

SM

D, C

A, L

carbamazepine (+)

Family A, III-3 (PKD)

c.776dupG

22y/F

African-American

10y

Yes

30-40/day

10-15 sec

SM

D, C

F, A, L

carbamazepine(+), phenytoin(+)

Family A, III-4 (PKD)

c.776dupG

18y/F

African-American

13y

Yes

20-30/day

10-60 sec

SM

D, C

F, A, L

carbamazepine(+)

Family B (PKD)

c.649dupC

30y/M

African-American

12y

Yes

50/day

10-60 sec

SM

D, C

F, A

phenytoin (+)

Case 7 (PKD)

c.649dupC

27y/M

Caucasian-Thai

21y

*Yes

3-6/day

< 10 sec

SM, S

D

F, A, L

carbamazepine (+)

Case 8 (PED)

None

29y/F

Caucasian

< 28y

No

< 1/day

2-4 hrs

Intense exercise

D

F, A, L

clonazepam (±)

Case 9 (PKD)

None

18y/M

Caucasian

14y

No

5-8/day

< 15 sec

SM

D

F, A, L

carbamazepine (+)

Case 10 (ICCA)

None

19mo/M

Caucasian

7 m

No

>100/day

40-50 sec

SM

D, C, A

F, A, L

carbamazepine (+)

Case 11 (PKD)

None

41y/F

Caucasian

< 33y

Yes

20-25/mo

2-30 min

SM, S

D

F, A, L

piracetam (±) clonazepam (±)

Case 12 (PKD)

None

20y/M

Caucasian

3y

No

6-7/day

5-60 sec

SM, S

D, C, A

F, A, L

carbamazepine (+)

Case 13 (PKD)

None

18y/M

Caucasian

15y

Yes

2-5/day

5-6 sec

SM

D

F, A, L

carbamazepine (+)

Case 14 (PKD)

None

18y/F

Caucasian

15y

No

3-4/day

< 10 sec

SM, S

D, C, A

F, A, L

carbamazepine (+)

Case 15 (PKD)

None

14y/M

Vietnamese

12y

No

10/day

15-60 sec

S

D

A, L

acetazolamide (+)

Case 16 (PKD)

None

26y/F

Caucasian

16y

No

30/day

20-30 sec

SM

D

A

phenytoin (+)

Case 17 (PNKD)

None

6y/F

Caucasian

6 m

Yes

2-10/mo

3-60 min

Fatigue, sleep deprivation

D

A, L

NA

Involuntary movements: D-dystonia, C-chorea, and A-athetosis. Anatomical distribution: F-face, A-arm, and L-leg.

Triggers: SM-sudden movement and S-stress. NA, DNA or clinical detail not available. Response to anticonvulsants:

+, good to excellent response and ±, partial response, *, early childhood seizures on maternal (Thai) side of the family.

DNA was extracted from peripheral blood leucocytes using Roche’s DNA Isolation Kit for Mammalian Blood (Indianapolis, IN, USA). DNA quantity and quality were analyzed with a NanoDrop ND-1000 spectrophotometer (Wilmington, DE, USA) and agarose gel electrophoresis. With Primer3 (frodo.wi.mit.edu), four pairs of PCR primers were designed to encompass the four PRRT2 exons and flanking intronic regions (Additional file 1 Table S1). For Sanger sequencing, PCR was performed using 50 ng of template DNA, 1X PCR buffer, 2.5 mM MgCl2 and 200 nM of each primer in a 20-μl reaction volume. The following cycling conditions were employed: 95°C for 15 min; 35 cycles at 95°C for 15 s, 60°C for 15 s, and 72°C for 45 s; and 72°C for 10 min. After agarose gel confirmation, 5 μl of the PCR products were cleaned using ExoSAP-IT® (United States Biochemical, Cleveland, OH, USA). Then, 1-2 μl of the purified PCR products were sequenced in the forward and reverse directions on the Applied Biosystems 3130XL Genetic Analyzer (Carlsbad, CA, USA). Control DNA samples (100 African-American and 100 Caucasian) were sequenced for detection of newly-identified PRRT2 mutations.

Results

Among 13 index cases with paroxysmal dyskinesias, two different mutations in three families were identified. A novel mutation was found in African-American Family A (Figure 1, c.776dupG, p.E260*). This mutation was not found in 100 African-American or 100 Caucasian normal controls. The proband was a 22-year-old female (Figure 1, III-3), who noticed the first attack of choreiform and dystonic movements in her hands and arms at age 12. Subsequent episodes also included dystonia in her legs and face. Her father and all three sisters have similar clinical features during attacks with dystonia in the face, arms and legs, along with chorea in the hands. Although DNA specimens were not available from her father and two older sisters, the c.776dupG mutation was confirmed in her youngest sister (III-4). All affected family members responded to either carbamazepine or phenytoin. Two of the three family members currently taking phenytoin did not tolerate carbamazepine due to sedative effects.
https://static-content.springer.com/image/art%3A10.1186%2F1471-2377-12-93/MediaObjects/12883_2012_Article_608_Fig1_HTML.jpg
Figure 1

African-American PKD pedigrees. Males are represented by squares, females by circles. Affected individuals are represented by filled/black symbols and asymptomatic family members by empty/white symbols. Symbols of deceased individuals are slashed. Probands are denoted with arrows.

The previously reported hotspot mutation (c.649dupC, p.R217Pfs*8) was found in African-American Family B (Figure 1) and an individual of mixed Caucasian-Thai background. The c.649dupC variant was not found in 100 African-American or 100 Caucasian normal controls. Case 7 had late-onset (>20 y) but otherwise classic carbamazepine-responsive PKD. Prior to initiation of therapy with carbamazepine, sudden movements were more likely to precipitate dystonic posturing when the patient was under psychological stress. Attacks often consisted of dystonic posturing of the left arm in abduction along with cervical dystonia. Occasionally, similar attacks affected the right side of the body. Although his Thai mother had no history of PKD, ICCA or BFIE and was found to be neurologically normal, Sanger sequencing revealed that she was a carrier, and several of her family members reportedly had infantile seizures.

No sequence variants were identified in the remaining 10 probands (9 Caucasian, 1 Vietnamese) with PED, ICCA, PKD or PNKD, 3 of whom had a positive family history. All but two of these individuals had early-onset (< 20 y) paroxysmal dyskinesias. Age of onset, attack frequency and attack duration were much more variable among the mutation-negative cases in comparison to the patients with PRRT2 mutations.

Discussion

Candidate regions for PKD and ICCA were mapped to Chr 16 over a decade ago. PKD was linked to a 15.8 cM region flanked by markers D16S685 and D16S503 on Chr 16q13-q22.1 with a maximum LOD score of 3.66 at D16S419 in a large Indian family [13]. This candidate region was telomeric to a locus identified in Japanese families with PKD [14], but showed overlap with a region identified in an African-American family with PKD [15]. A candidate region for ICCA had also been mapped to the pericentromeric region of Chr 16 in French [16] and Chinese [17] families.

Just recently, several distinct loss-of-function frameshift mutations leading to protein truncation or nonsense-mediated decay in proline-rich transmembrane protein 2 (PRRT2) have been associated with PKD in numerous Han Chinese families [36]. A much smaller percentage of cases were associated with missense mutations (e.g., c.796C > T, p.R266W; c.913 G > A, p.G305R) [4, 6]. In addition to classic carbamazepine-responsive PKD, the phenotypic spectrum of PRRT2 mutations includes cases of ICCA, BFIE, some “PNKD-like” syndromes, and PED [611]. PRRT2 is located on Chr 16p11.2, within the ICCA, Japanese PKD, and African-American candidate regions but outside the Indian PKD candidate region. The association of PRRT2 genotypes with specific neurological phenotypes may become apparent with the publication of additional well-characterized cases.

PRRT2 is a cell surface protein containing two predicted transmembrane domains and highly expressed in the developing nervous system, particularly the cerebellum [3]. Our study has shown that novel and hotspot mutations in PRRT2 are associated with classic PKD in African-Americans. The c.776dupG and c.649dupC mutations are heterozygous SNindels (single nucleotide insertions or deletions) predicted to cause nonsense-mediated decay of mutant transcripts rather than expression of a truncated protein [18, 19]. SNindels occur at an estimated frequency of 0.887 per 10 kb of genomic DNA with more than half occurring in regions with mononucleotide repeats [19]. The novel c.776dupG mutation is located within a 6 nucleotide (nt) poly-G tract and the c.649dupC hot spot mutation is in a 9 nt poly-C tract. SNindels within regions of mononucleotide repeats may arise from replication slippage [19].

Conclusions

The novel c.776dupG mutation and c.649dupC hot spot mutation identified in our African-American families with classic PKD expands the molecular and racial spectrums of PRRT2 mutations. As evidenced from our patient of mixed Caucasian-Thai descent, the penetrance of PRRT2 mutations may depend on the origin of the normal or wild-type allele. Finally, a significant percentage of patients with PKD and ICCA do not harbor mutations in coding regions of PRRT2.

Notes

Abbreviations

PKD: 

Paroxysmal kinesigenic dyskinesia

EKD1: 

Episodic kinesigenic dyskinesia

PKC: 

Paroxysmal kinesigenic choreoathetosis

ICCA: 

Infantile convulsions and choreoathetosis

BFIE: 

Benign familial infantile epilepsy

PED: 

Paroxysmal exercise-induced dyskinesia

PNKD: 

Paroxysmal non-kinesigenic dyskinesia.

Declarations

Funding agencies

At the University of Tennessee Health Science Center, this study was supported by the Neuroscience Institute (MSL), Dystonia Medical Research Foundation (MSL), NIH grants R01NS048458 (MSL) and R01NS069936 (MSL), and the NIH Dystonia Coalition Pilot Projects Program (U54NS065701). PH was supported by NIH/NINDS K02NS057666.

Full financial disclosures

Dr. Hedera serves on the speakers’ bureau for Lundbeck. Dr. Xiao has nothing to disclose. Dr. Puschmann receives research support from governmental funding of clinical research within the Swedish National Health Services (ALF-YF), the Swedish Parkinson Foundation (Parkinsonfonden), and The Swedish Parkinson Academy (SPA); received compensation for travel expenses from The Swedish Dystonia Society (Svensk dystoniförening). Dr. Momčilović has nothing to disclose. Dr. Wu receives research support from NIH-NINDS Pediatric Research Loan Repayment Program and the Tourette Syndrome Association. He is also involved in clinical trials conducted by Genzyme Corporation, Otsuka Pharmaceuticals Inc. and Psyadon Pharmaceuticals Inc. Dr. LeDoux serves on the speakers’ bureaus for Lundbeck, Merz, and Teva Neuroscience; serves as an advisor for Merz; serves on the Xenazine Advisory Board for Lundbeck, Inc., and the Botulinum Toxin Type A Advisory Board for Allergan; receives research support from the NIH, Dystonia Medical Research Foundation, and Merz; and receives royalty payments for Animal Models of Movement Disorders (Elsevier).

Acknowledgements

We gratefully acknowledge the assistance of Y. Zhao, S. Vemula, and K. Marshall with sample processing.

Authors’ Affiliations

(1)
Department of Neurology, Vanderbilt University
(2)
Departments of Neurology, and Anatomy and Neurobiology, University of Tennessee Health Science Center
(3)
Department of Neurology, Skåne University Hospital and Department of Neurology, Lund University
(4)
Clinic for Child Neurology and Psychiatry, Medical Faculty University of Belgrade
(5)
Department of Pediatrics, University of Cincinnati

References

  1. Bruno MK, Hallett M, Gwinn-Hardy K, Sorensen B, Considine E, Tucker S, Lynch DR, Mathews KD, Swoboda KJ, Harris J, Soong BW, Ashizawa T, Jankovic J, Renner D, Fu YH, Ptacek LJ: Clinical evaluation of idiopathic paroxysmal kinesigenic dyskinesia: new diagnostic criteria. Neurology. 2004, 63: 2280-2287. 10.1212/01.WNL.0000147298.05983.50.View ArticlePubMedGoogle Scholar
  2. Bhatia KP: Paroxysmal dyskinesias. Mov Disord. 2011, 26: 1157-1165. 10.1002/mds.23765.View ArticlePubMedGoogle Scholar
  3. Chen WJ, Lin Y, Xiong ZQ, Wei W, Ni W, Tan GH, Guo SL, He J, Chen YF, Zhang QJ, Li HF, Lin Y, Murong SX, Xu J, Wang N, Wu ZY: Exome sequencing identifies truncating mutations in PRRT2 that cause paroxysmal kinesigenic dyskinesia. Nature Genet. 2011, 43: 1252-1255. 10.1038/ng.1008.View ArticlePubMedGoogle Scholar
  4. Wang JL, Cao L, Li XH, Hu ZM, Li JD, Zhang JG, Liang Y, San A, Li N, Chen SQ, Guo JF, Jiang H, Shen L, Zheng L, Mao X, Yan WQ, Zhou Y, Shi YT, Ai SX, Dai MZ, Zhang P, Xia K, Chen SD, Tang BS: Identification of PRRT2 as the causative gene of paroxysmal kinesigenic dyskinesias. Brain. 2011, 134: 3493-3501. 10.1093/brain/awr289.View ArticlePubMedGoogle Scholar
  5. Li J, Zhu X, Wang X, Sun W, Feng B, Du T, Sun B, Niu F, Wei H, Wu X, Dong L, Li L, Cai X, Wang Y, Liu Y: Targeted genomic sequencing identifies PRRT2 mutations as a cause of paroxysmal kinesigenic choreoathetosis. J Med Genet. 2012, 49: 76-78. 10.1136/jmedgenet-2011-100635.View ArticlePubMedGoogle Scholar
  6. Liu Q, Qi Z, Wan XH, Li JY, Shi L, Lu Q, Zhou XQ, Qiao L, Wu LW, Liu XQ, Yang W, Liu Y, Cui LY, Zhang X: Mutations in PRRT2 result in paroxysmal dyskinesias with marked variability in clinical expression. J Med Genet. 2012, 49: 79-82. 10.1136/jmedgenet-2011-100653.View ArticlePubMedGoogle Scholar
  7. Heron SE, Grinton BE, Kivity S, Afawi Z, Zuberi SM, Hughes JN, Pridmore C, Hodgson BL, Iona X, Sadleir LG, Pelekanos J, Herlenius E, Goldberg-Stern H, Bassan H, Haan E, Korczyn AD, Gardner AE, Corbett MA, Gécz J, Thomas PQ, Mulley JC, Berkovic SF, Scheffer IE, Dibbens LM: PRRT2 mutations cause benign familial infantile epilepsy and infantile convulsions with choreoathetosis syndrome. Am J Hum Genet. 2012, 90: 152-160. 10.1016/j.ajhg.2011.12.003.View ArticlePubMedPubMed CentralGoogle Scholar
  8. Cao L, Huang XJ, Zheng L, Xiao Q, Wang XJ, Chen SD: Identification of a novel PRRT2 mutation in patients with paroxysmal kinesigenic dyskinesias and c.649dupC as a mutation hot-spot. Parkinsonism Relat Disord. 2012, 18: 704-706. 10.1016/j.parkreldis.2012.02.006.View ArticlePubMedGoogle Scholar
  9. Ono S, Yoshiura KI, Kinoshita A, Kikuchi T, Nakane Y, Kato N, Sadamatsu M, Konishi T, Nagamitsu S, Matsuura M, Yasuda A, Komine M, Kanai K, Inoue T, Osamura T, Saito K, Hirose S, Koide H, Tomita H, Ozawa H, Niikawa N, Kurotaki N: Mutations in PRRT2 responsible for paroxysmal kinesigenic dyskinesias also cause benign familial infantile convulsions. J Hum Genet. 2012, 57: 338-341. 10.1038/jhg.2012.23.View ArticlePubMedGoogle Scholar
  10. Lee HY, Huang Y, Bruneau N, Roll P, Roberson ED, Hermann M, Quinn E, Maas J, Edwards R, Ashizawa T, Baykan B, Bhatia K, Bressman S, Bruno MK, Brunt ER, Caraballo R, Echenne B, Fejerman N, Frucht S, Gurnett CA, Hirsch E, Houlden H, Jankovic J, Lee WL, Lynch DR, Mohamed S, Müller U, Nespeca MP, Renner D, Rochette J, et al: Mutations in the novel protein PRRT2 cause paroxysmal kinesigenic dyskinesia with infantile convulsions. Cell Rep. 2012, 1: 2-12. 10.1016/j.celrep.2011.11.001.View ArticlePubMedGoogle Scholar
  11. Schubert J, Paravidino R, Becker F, Berger A, Bebek N, Bianchi A, Brockmann K, Capovilla G, Dalla Bernardina B, Fukuyama Y, Hoffmann GF, Jurkat-Rott K, Antonnen AK, Kurlemann G, Lehesjoki AE, Lehmann-Horn F, Mastrangelo M, Mause U, Müller S, Neubauer B, Püst B, Rating D, Robbiano A, Ruf S, Schroeder C, Seidel A, Specchio N, Stephani U, Striano P, Teichler J, et al: PRRT2 mutations are the major cause of benign familial infantile seizures (BFIS). Hum Mutat. 2012, 33: 1439-1443. 10.1002/humu.22126.View ArticlePubMedGoogle Scholar
  12. Spacey SD, Valente EM, Wali GM, Warner TT, Jarman PR, Schapira AH, Dixon PH, Davis MB, Bhatia KP, Wood NW: Genetic and clinical heterogeneity in paroxysmal kinesigenic dyskinesia: evidence for a third EKD gene. Mov Disord. 2002, 17: 717-725. 10.1002/mds.10126.View ArticlePubMedGoogle Scholar
  13. Valente EM, Spacey SD, Wali GM, Bhatia KP, Dixon PH, Wood NW, Davis MB: A second paroxysmal kinesigenic choreoathetosis locus (EKD2) mapping on 16q13-q22.1 indicates a family of genes which give rise to paroxysmal disorders on human chromosome 16. Brain. 2000, 123: 2040-2045. 10.1093/brain/123.10.2040.View ArticlePubMedGoogle Scholar
  14. Tomita H, Nagamitsu S, Wakui K, Fukushima Y, Yamada K, Sadamatsu M, Masui A, Konishi T, Matsuishi T, Aihara M, Shimizu K, Hashimoto K, Mineta M, Matsushima M, Tsujita T, Saito M, Tanaka H, Tsuji S, Takagi T, Nakamura Y, Nanko S, Kato N, Nakane Y, Niikawa N: Paroxysmal kinesigenic choreoathetosis locus maps to chromosome 16p11.2–q12.1. Am J Hum Genet. 1999, 65: 1688-1697. 10.1086/302682.View ArticlePubMedPubMed CentralGoogle Scholar
  15. Bennett LB, Roach ES, Bowcock AM: A locus for paroxysmal kinesigenic dyskinesia maps to human chromosome 16. Neurology. 2000, 54: 125-130. 10.1212/WNL.54.1.125.View ArticlePubMedGoogle Scholar
  16. Szepetowski P, Rochette J, Berquin P, Piussan C, Lathrop GM, Monaco AP: Familial infantile convulsions and paroxysmal choreoathetosis: a new neurological syndrome linked to the pericentromeric region of human chromosome 16. Am J Hum Genet. 1997, 61: 889-898. 10.1086/514877.View ArticlePubMedPubMed CentralGoogle Scholar
  17. Lee WL, Tay A, Ong HT, Goh LM, Monaco AP, Szepetowski P: Association of infantile convulsions with paroxysmal dyskinesias (ICCA syndrome): confirmation of linkage to human chromosome 16p12-q12 in a Chinese family. Hum Genet. 1998, 103: 608-612. 10.1007/s004390050876.View ArticlePubMedGoogle Scholar
  18. Silva AL, Romão L: The mammalian nonsense-mediated mRNA decay pathway: to decay or not to decay! Which players make the decision?. FEBS Lett. 2009, 583: 499-505. 10.1016/j.febslet.2008.12.058.View ArticlePubMedGoogle Scholar
  19. Tan EC, Li H: Characterization of frequencies and distribution of single nucleotide insertions/ deletions in the human genome. Gene. 2006, 376: 268-280. 10.1016/j.gene.2006.04.009.View ArticlePubMedGoogle Scholar
  20. Pre-publication history

    1. The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2377/12/93/prepub

Copyright

© Hedera et al.; licensee BioMed Central Ltd. 2012

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Advertisement