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  <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_AnnualMinimumRoyaltyPaymentsAfterFirstCommercialSale" name="AnnualMinimumRoyaltyPaymentsAfterFirstCommercialSale" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="atha_CashAndCashEquivalentsAccumulatedGrossUnrealizedGainBeforeTax" name="CashAndCashEquivalentsAccumulatedGrossUnrealizedGainBeforeTax" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
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  <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_EntityReincorporationDateOfReincorporation" name="EntityReincorporationDateOfReincorporation" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
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  <xsd:element id="atha_IncreaseDecreaseInUnbilledGrantReceivables" name="IncreaseDecreaseInUnbilledGrantReceivables" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="atha_IssuanceOfCommonStockSharesDuringPeriodFollowOnPublicOfferingNetOfUnderwritersDiscountsAndCommissions" name="IssuanceOfCommonStockSharesDuringPeriodFollowOnPublicOfferingNetOfUnderwritersDiscountsAndCommissions" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="atha_IssuanceOfCommonStockUponExerciseOfCommonStockOptionsAndVestingOfRestrictedStockUnits" name="IssuanceOfCommonStockUponExerciseOfCommonStockOptionsAndVestingOfRestrictedStockUnits" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
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  <xsd:element id="atha_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearThree" name="LesseeOperatingLeaseLiabilityPaymentsDueAfterYearThree" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
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  <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_MilestonePaymentsAmountPayableUponTrialInitiation" name="MilestonePaymentsAmountPayableUponTrialInitiation" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
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  <xsd:element id="atha_OperatingLeaseExpirationMonthAndYear" name="OperatingLeaseExpirationMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="atha_PaymentOnAchievementOfDevelopmentMilestone" name="PaymentOnAchievementOfDevelopmentMilestone" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
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  <xsd:element id="atha_ProceedsFromIssuanceOfConvertiblePreferredStockAndCommonStockWarrants" name="ProceedsFromIssuanceOfConvertiblePreferredStockAndCommonStockWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
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  <xsd:element id="atha_LicensedProductsMember" name="LicensedProductsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
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  <xsd:element id="atha_SharesIssuableUponTheExerciseOfOutstandingCommonStockOptionsAndTheVestingOfOutstandingCommonRestrictedStockUnitsGrantedMember" name="SharesIssuableUponTheExerciseOfOutstandingCommonStockOptionsAndTheVestingOfOutstandingCommonRestrictedStockUnitsGrantedMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
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  <xsd:element id="atha_USGovernmentDebtMunicipalBondsAndAgencySecuritiesMember" name="USGovernmentDebtMunicipalBondsAndAgencySecuritiesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
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  <xsd:element id="atha_EmergingGrowthCompanyStatusPolicyTextBlock" name="EmergingGrowthCompanyStatusPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
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  <xsd:element id="atha_UnauditedInterimCondensedFinancialStatementsPolicyTextBlock" name="UnauditedInterimCondensedFinancialStatementsPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
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  <xsd:element id="atha_CommitmentAndContingenciesTable" name="CommitmentAndContingenciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" 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_ScheduleOfReservedSharesOfCommonStockForFutureIssuanceTableTextBlock" name="ScheduleOfReservedSharesOfCommonStockForFutureIssuanceTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="atha_ScheduleOfShareBasedCompensationArrangementSharesAvailableForGrantTableTextBlock" name="ScheduleOfShareBasedCompensationArrangementSharesAvailableForGrantTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="atha_ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock" name="ScheduleOfCashCashEquivalentsAndRestrictedCashTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
</xsd:schema>
