TheDNACommissionoftheInternationalSocietyforForensicHaemogenetics(ISFH) hasovertheyears,pub-lished a series of documents providing guidelines and re-commendations concerning the application of DNA poly-morphisms to problems of identification.Thelatestreportpublishedhere,providesrecommen-dations relating to the nomenclature of STR (short tandemrepeat)typingsystemswhichareattheforefrontofsys-tems used at present by forensic scientists and are likely toremain so for the immediate future.Also included in this number of the Journal is a paperbytheEuropeanDNA ProfilingGroup(EDNAP)whichalsodiscussesandprovidesguidelinesconcerningthenomenclatureofSTRsystemsandassuchcomplementsthe report of the DNA Commission of the ISFH.IntroductionA common nomenclature for STRs is a prerequisite for in-terlaboratoryreproducibilityandfortheexchangeandcomparison of data. For many loci there has been an enor-mousincreaseofinformationaboutsequenceandsub-structure which has repeatedly raised questions relating tonomenclature.Whilethepreviousrecommendationsarestill valid, here we describe some additional rules relatingto STR allele designation.1. Sequence and repeat designation of STRsDNAsequencesarereadinthe5 to3 direction.Thechoice of the strand also influences the sequence designa-tion. To avoid confusion, the following guidelines shouldbe followed: For STRs within protein coding genes (as well as in theintron of the genes), the coding strand should be used. AnexampleofsuchalocusisvWA(GenBank:M25716).Thesameappliestopseudogenes,suchastheACTBP2locus,wherethestrandwiththesequencesimilartothecoding strand of the original gene should be used (Moosand Gallwitz 1983). For repetitive sequences without any connection to pro-teincodinggeneslikemanyoftheD#S##loci,these-quenceoriginallydescribedintheliteratureorthefirstpublic database entry shall become the standard reference(and strand) for nomenclature.If a nomenclature is already established in the forensicfieldbutnotinaccordancewiththeaforementionedguideline,thenomenclatureshallbemaintainedtoavoidunnecessary confusion.Itissometimespossibletodefinedifferentrepetitivemotifs, even though the choice of the strand is clear. In thetwofollowingexamples,theinitialpointforreadingtherepeat motif is different for the same sequence:1. 5-GG TCA TCA TCA TGG-3 3 TCA2. 5-GGT CAT CAT CAT GG-3 3 CATThe recommendation is that the repeat sequence motifmust be defined so that the first 5-nucleotides that can de-fine a repeat motif are used. Thus only the first renditionis correct.Thesetworulestogether,forthechoiceofthestrandand for the choice of the motif, will allow for the defini-tionofthesequenceandrepeatdesignationofanynewSTR.IfarepeatdesignationofacommonlyusedSTRsystemdoesnotfollowtheseguidelines,theestablishednomenclature for the sequence can continue to be used toavoidnewconfusion.Forthosesituationswheretwoormore nomenclatures already exist, priority should be givento the nomenclature that more closely adheres to the guide-linesdescribedhere.Ifthisisnotpossible,priorityshallbe given to the nomenclature that was documented first.W. Br B. Brinkmann B. Budowle A. Carracedo P. Gill P. Lincoln W. Mayr B. OlaisenDNA recommendationsFurther report of the DNA Commission* of the ISFH regarding the use of short tandem repeat systemsInt J Legal Med (1997) 110: 175176 Springer-Verlag 1997EDITORIAL* Members of the DNA Commission of the ISFH:B. Olaisen, W. Br, W. Mayr, P. Lincoln, A. Carracedo, B. Brinkmann, B. Budowle and P. GillReprints from: B. Brinkmann,Institut fr Rechtsmedizin, Von-Esmarch-Strasse 86, D-48149 Mnster, GermanyFAX: +49 (251) 8355 158e-mail: brinkma@uni-muenster.de2. Allele designation of STRsSince the polymorphisms concerned are defined by varia-tionsinthenumberofrepeats(VNTRs),alleledesigna-tion basically should observe this structural principle. For simple systems like HumFES/FPS, (ATTT)814, thisis straightforward. For systems composed of repeat regions where the se-quence may vary, designation of alleles should refer to thetotal number of full repeats, although the sequence can bedifferent(asforHumVWAorthelongerHumCD4alle-les). The designation of incomplete repeat motifs should in-cludethenumberofcompleterepeatsand,separatedby adecimalpoint,thenumberofbasepairsintheincom-plete repeat. Examples are allele 9.3 at the HumTH01 lo-cus, (Puers et al. 1993) which contains nine tetranucleotiderepeatsandoneincompleterepeatofthreenucleotidesandtheallele22.2attheFGAlocus,whichcontains22tetranucleotiderepeatsandoneincompleterepeatwithtwo nucleotides only (Barber et al. 1996).Forcomplexrepeatsystems,repeatnomenclatureshouldhaveamathematicalrelationshiptothelengthinbpoftheconsensusallele.AnexampleisD21S11(Brinkmann et al. 1996):repeats length relation27 213 bp 27 4 + 105 = 21331 229 bp 31 4 + 105 = 22933.2 239 bp 33 4 + 2 + 105 = 239,where 105 bp is the sum of the 5-flanking region, the 3-flankingregionandaninterspread43bpconstantarray.This kind of nomenclature allows for the easy conversionof the results from automated typing in bp into the repeatbasednomenclaturereferringtocommonandconsensusalleles in the ladder.For some highly variable systems (such as the ACTBP2locus),therepetitivestructurecanbeverycomplexandthe definition of a consensus repeat structure can be diffi-cult. In such cases, alleles should be identified accordingto their size in bp, by comparison with a sequenced ladder.Sequence variants of the same length in these highly vari-able systems can have different electrophoretic mobilitiesunder certain conditions. Thus the type of the allele deter-mined will depend on the electrophoretic system used. Tominimiseelectrophoreticmobilitydifferencesforalleles,thesesystemsshouldbetypedpreferablyunderdenatur-ing conditions.3. Use of allelic laddersAllelic ladders are used as a reference for allele designa-tion.Allallelesinanallelicladdershouldbesequencedandnominatedaccordingtotheaforementionedrules.They can be obtained commercially or prepared in house.Laddersshouldcontainallcommonalleles,sothatthespacing allows for exact typing of the samples (this is a 4 bpspacing for many of the common tetranucleotide repeats).Typingcanbecarriedoutusingmanualorautomatedmethods.Allelesinadatabaseorinidentitytestingarenamed according to the visual comparison with an allelicladder or by automated sizing using standards, sequencingis not necessary. The base composition can influence theelectrophoreticmobility,allelesoftherespectivesystemshould be used as standard for automated sizing wheneverpossible. Results in bp must be converted into the repeat-basednames(whenpossible,seeabove).Aprerequisitefor typing is that the resolution of the electrophoretic sys-temusedallowsforthedetectionandpreciseidentifica-tionofallcommonalleles.Insomehighlyvariablesys-tems,alleleswith2bpdifferencestothenextcommonlonger and smaller allele are observed (e.g. allele 22, 22.2and 23 at the FGA locus or many of the ACTBP2 alleles).Manualtypingofthislocusshouldallowfortherepro-ducibledetectionofthesealleles.Automatedfragmentsizing should have a typing error smaller than half of thedistance between common alleles (otherwise a continuousallele distribution would result).The separation and detection system can influence thenumberofvariants/allelesdetected.Forexample,somelaboratories distinguish between alleles 9.3 and 10 at theTH01 locus, some do not. The same is true for variants ofallele 10 at the FES locus, which have either an A or a Cin the 5-flanking region. These differences between labo-ratories are relevant to questions of reproducibility and re-sult sharing. Allele frequencies depend on the correct de-finitionofallelesasdistinguishableentities.Itshouldbeclear whether variants have been detected or not. Apply-ing the above rules for the TH01 locus, the pooled allelefrequencies in the database must be nominated 9.3/10. Atthe FES locus, allele 10 includes both variants, with the Aand the C in the 5-flanking region. If the variants are de-tected, they should be designated 10Adeor 10Cyt. (10A or Cwouldconfusepeopleusingtheabbreviationsforelec-trophoretic shifts to the anode or the cathode).Informationonelectrophoreticconditions,theladdersused,theprimersequencesandthedetectionsystemshouldbemadeavailableuponthepublicationofdata.Authorsshouldfollowtheserecommendationsandstatethat they did so.ReferencesBarber MD, McKeown BJ, Parkin B (1996) Structural variation inthe alleles of a short tandem repeat system at the human alphafibrinogen locus. Int J Legal Med 108: 180185BrinkmannB,MeyerE,JungeA(1996)Complexmutationalevents at the HumD21S11 locus. Hum Genet 98: 6064MoosM,GallwitzD(1983)Structureoftwohuman-actin-re-lated processed genes one of which is located next to a simplerepetitive sequence. EMBO J 2: 757761PuersC,HammondHA,JinL,CaskeyCT,SchummJW(1993)Identification of repeat sequence heterogeneity at the polymor-phic short tandem repeat locus HUMTH01 (AATG)nand reas-signment of alleles in population analysis by using a locus-spe-cific allelic ladder. Am J Hum Genet 53: 953958176 W. Br et al.: DNA recommendations