The DistinguishedName element contains the distinguished name of the domain.

 <xs:element name="DistinguishedName" nillable="true" type="xs:string" />

The DistinguishedName element is populated from the domainDNS!distinguishedName attribute on the domain NC root object ([MS-ADTS] section If the domainDNS!distinguishedName attribute is not present or cannot be read due to the client lacking access rights to read the attribute, the server returns a null ActiveDirectoryPartition/DistinguishedName.