ALK7:actriib heteromultimers and uses thereof

A method of treating a kidney disorder in a subject in need thereof, comprising administering to the subject a soluble recombinant heteromultimer comprising:

• (i) an ALK7 polypeptide comprising an amino acid sequence that is at least 90% identical to amino acids 28-92 of SEQ ID NO:
• 9, and
• (ii) an ActRIIB polypeptide comprising an amino acid sequence that is at least 90% identical to amino acids 29-109 of SEQ ID NO:
• 1, and
• wherein the heteromultimer binds to one or more of:
• activin B, activin C, and activin AC;
• and
• wherein the kidney disorder is selected from a group consisting of kidney fibrosis and kidney inflammation.