Why Did Centessa's Shares Plunge 10% Today?

Centessa Pharmaceuticals plc CNTA announced proof-of-mechanism data from the first three subjects in Phase 1 Part B study of ZF874 in Alpha-1 Antitrypsin Deficiency (AATD).
AATD is an autosomal recessive disorder frequently caused by missense mutations in the A1AT gene.
Individuals with AATD regularly suffer from chronic obstructive pulmonary disease and/or liver disease.
In both PiMZ subjects dosed with 15 mg/kg BID of ZF874, the observed increase in functional A1AT was between 3.5 and 6 micromolar.
Consistent with a pharmacological effect for ZF874, A1AT levels returned to baseline by 28 days after dosing.
Pharmacokinetic analysis showed a two-fold higher exposure to ZF874 in one subject.
CNTA shares are plunging as investors react when this one subject did show a two-fold increase in functional A1AT but also experienced severe liver toxicity, with a delayed, reversible increase in ALT and AST (enzymes suggesting liver damage).
All other liver function tests remained in the normal range.
Read Next: Centessa Stock Surges On Positive Data From Hemophilia Candidate.
Price Action: CNTA shares are down 18.55% at $14.01 on Monday.