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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2021-03-25T00:56:27.9381165+00:00 -->
<!-- Version            : 5.0.1.571 -->
<!-- Package ID         : 1aebdd01ac0b40848ed8122f88ba18e5 -->
<!-- Copyright (c) 2021 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="atha_ScheduleOfReservedSharesOfCommonStockForFutureIssuanceTableTextBlock" name="ScheduleOfReservedSharesOfCommonStockForFutureIssuanceTableTextBlock" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_DescriptionOfBusinessLineItems" name="DescriptionOfBusinessLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_DescriptionOfBusinessTable" name="DescriptionOfBusinessTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_CommonStockWarrantsMember" name="CommonStockWarrantsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_SeriesBConvertiblePreferredStockWarrantMember" name="SeriesBConvertiblePreferredStockWarrantMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ConvertiblePreferredStockCommonStockWarrantsOrSeriesBConvertiblePreferredStockWarrantsMember" name="ConvertiblePreferredStockCommonStockWarrantsOrSeriesBConvertiblePreferredStockWarrantsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_CommonSharesIssuedUponExerciseOfWarrants" name="CommonSharesIssuedUponExerciseOfWarrants" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_ProceedsFromIssuanceOfConvertiblePreferredStockAndCommonStockWarrants" name="ProceedsFromIssuanceOfConvertiblePreferredStockAndCommonStockWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_CashCashEquivalentsAndShortTermAndLongTermInvestments" name="CashCashEquivalentsAndShortTermAndLongTermInvestments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_BasisOfPresentationAndSignificantAccountingPoliciesLineItems" name="BasisOfPresentationAndSignificantAccountingPoliciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_BasisOfPresentationAndSignificantAccountingPoliciesTable" name="BasisOfPresentationAndSignificantAccountingPoliciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_AlzheimersAssociationMember" name="AlzheimersAssociationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_AccruedExpensesMember" name="AccruedExpensesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_NationalInstituteOnAgingOfTheNationalInstitutesOfHealthMember" name="NationalInstituteOnAgingOfTheNationalInstitutesOfHealthMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_UnbilledGrantReceivableMember" name="UnbilledGrantReceivableMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_UnsecuredRelatedPartyNoteReceivableMember" name="UnsecuredRelatedPartyNoteReceivableMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_GrantLiabilityCurrent" name="GrantLiabilityCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_GrantsAwarded" name="GrantsAwarded" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_ResearchGrantIncomeNonoperating" name="ResearchGrantIncomeNonoperating" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_GrantsReceived" name="GrantsReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_GrantsAmountIncurredQualifyingExpensesInExcessOfAmountReceived" name="GrantsAmountIncurredQualifyingExpensesInExcessOfAmountReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_GrantsAmountReceivedInExcessOfQualifyingExpense" name="GrantsAmountReceivedInExcessOfQualifyingExpense" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_RemainingGrantAmount" name="RemainingGrantAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_CashAndCashEquivalentsAccumulatedGrossUnrealizedGainBeforeTax" name="CashAndCashEquivalentsAccumulatedGrossUnrealizedGainBeforeTax" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_CashAndCashEquivalentsAccumulatedGrossUnrealizedLossBeforeTax" name="CashAndCashEquivalentsAccumulatedGrossUnrealizedLossBeforeTax" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_LongTermInvestmentsMember" name="LongTermInvestmentsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_LongTermInvestmentsMaturityTerm" name="LongTermInvestmentsMaturityTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_ShortTermInvestmentsMaturityTerm" name="ShortTermInvestmentsMaturityTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_LaboratoryEquipmentMember" name="LaboratoryEquipmentMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_AccruedResearchAndDevelopmentExpensesCurrent" name="AccruedResearchAndDevelopmentExpensesCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_AccruedProfessionalServicesAndOtherCurrent" name="AccruedProfessionalServicesAndOtherCurrent" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_ChangeInFairValueOfDerivativeLiability" name="ChangeInFairValueOfDerivativeLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_PaymentOnAchievementOfDevelopmentMilestone" name="PaymentOnAchievementOfDevelopmentMilestone" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_MilestonePaymentsAmountPayableUponTrialInitiation" name="MilestonePaymentsAmountPayableUponTrialInitiation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_MilestonePaymentsAmountPayableUponMarketingApproval" name="MilestonePaymentsAmountPayableUponMarketingApproval" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_WashingtonStateUniversityLicenseAgreementMember" name="WashingtonStateUniversityLicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_PhaseTwoClinicalTrailInitiationOfLicenseAgreementMember" name="PhaseTwoClinicalTrailInitiationOfLicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_PhaseThreeClinicalTrailInitiationOfLicenseAgreementMember" name="PhaseThreeClinicalTrailInitiationOfLicenseAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_WashingtonLifeServicesDiscoveryFundGrantAgreementMember" name="WashingtonLifeServicesDiscoveryFundGrantAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_AnnualMinimumRoyaltyPaymentsAfterFirstCommercialSale" name="AnnualMinimumRoyaltyPaymentsAfterFirstCommercialSale" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_NetSalesExemptFromRoyaltyPayment" name="NetSalesExemptFromRoyaltyPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_RoyaltyObligation" name="RoyaltyObligation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_GrantLiabilityMaximumAmountPayableUnderAgreement" name="GrantLiabilityMaximumAmountPayableUnderAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_EstimatedFairValueOfGrantLiability" name="EstimatedFairValueOfGrantLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_DebtInstrumentMaturityMonthAndYear" name="DebtInstrumentMaturityMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_UnsecuredConvertibleNotesMember" name="UnsecuredConvertibleNotesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_SeriesB1ConvertiblePreferredStockMember" name="SeriesB1ConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_OperatingLeaseExpirationMonthAndYear" name="OperatingLeaseExpirationMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_LaboratoryAndOfficeFacilitiesMember" name="LaboratoryAndOfficeFacilitiesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_BothellWashingtonMember" name="BothellWashingtonMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_UniversityOfWashingtonSeattleMember" name="UniversityOfWashingtonSeattleMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_SeriesAConvertiblePreferredStockMember" name="SeriesAConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_SeriesA1ConvertiblePreferredStockMember" name="SeriesA1ConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ClassOfWarrantOrRightExercised" name="ClassOfWarrantOrRightExercised" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="atha_ConvertiblePreferredStockConversionPrice" name="ConvertiblePreferredStockConversionPrice" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="atha_ConvertiblePreferredStockConversionPricePercentage" name="ConvertiblePreferredStockConversionPricePercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_SeriesBConvertiblePreferredStockMember" name="SeriesBConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ClassOfWarrantOrRightPurchasePriceOneMember" name="ClassOfWarrantOrRightPurchasePriceOneMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_StockOptionsOutstandingMember" name="StockOptionsOutstandingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_SharesAvailableForFutureGrantUnderTwoThousandTwentyEquityIncentivePlanMember" name="SharesAvailableForFutureGrantUnderTwoThousandTwentyEquityIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_SharesAvailableForFutureGrantUnderEmployeeStockPurchasePlanMember" name="SharesAvailableForFutureGrantUnderEmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_EmployeesAndDirectorsMember" name="EmployeesAndDirectorsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_AdvisorsMember" name="AdvisorsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_NonEmployeesMember" name="NonEmployeesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_TwoThousandTwentyEmployeeStockPurchasePlanMember" name="TwoThousandTwentyEmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageGrantDateFairValueOfOptionsGranted" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageGrantDateFairValueOfOptionsGranted" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantAuthorized" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantAuthorized" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantGranted" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantGranted" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantForfeitedAndExpired" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantForfeitedAndExpired" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePrice" name="ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePrice" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_ExercisePriceOneMember" name="ExercisePriceOneMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceTwoMember" name="ExercisePriceTwoMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceThreeMember" name="ExercisePriceThreeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceFourMember" name="ExercisePriceFourMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceFiveMember" name="ExercisePriceFiveMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceSixMember" name="ExercisePriceSixMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceSevenMember" name="ExercisePriceSevenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceEightMember" name="ExercisePriceEightMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceNineMember" name="ExercisePriceNineMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceTenMember" name="ExercisePriceTenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceElevenMember" name="ExercisePriceElevenMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ExercisePriceTwelveMember" name="ExercisePriceTwelveMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_ShareBasedCompensationArrangementByShareBasedPaymentAwardSubjectToRepurchaseUponDiscontinuedService" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardSubjectToRepurchaseUponDiscontinuedService" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="atha_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumPercentageOfPayrollDeductionsForQualifyingWagesOrStatutoryLimit" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumPercentageOfPayrollDeductionsForQualifyingWagesOrStatutoryLimit" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRelatedToConvertibleNotesAndDerivativeLiability" name="EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRelatedToConvertibleNotesAndDerivativeLiability" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRelatedToGrantLiability" name="EffectiveIncomeTaxRateReconciliationNondeductibleExpenseRelatedToGrantLiability" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_DeferredTaxAssetsOperatingLeaseLiability" name="DeferredTaxAssetsOperatingLeaseLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="atha_DeferredTaxAssetsRightOfUseAsset" name="DeferredTaxAssetsRightOfUseAsset" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="atha_NetOperatingLossAndTaxCreditCarryForwardsExpirationPeriod" name="NetOperatingLossAndTaxCreditCarryForwardsExpirationPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="atha_ConvertiblePreferredStockOnConvertedBasisMember" name="ConvertiblePreferredStockOnConvertedBasisMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_UnvestedRestrictedStockAwardsMember" name="UnvestedRestrictedStockAwardsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_StockOptionsToPurchaseCommonStockMember" name="StockOptionsToPurchaseCommonStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="atha_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
</xsd:schema>
