December 30, 2019

Dear global HD community,

Today we announced encouraging topline results from PRECISION-HD2, our ongoing Phase
1b/2a placebo-controlled trial evaluating the investigational therapy WVE-120102
targeting SNP2. In an analysis of the study results, we compared all patients treated with
WVE-120102 to patients who received placebo and saw a statistically significant reduction
of 12.4% (p<0.05) in mutant huntingtin protein in the cerebrospinal fluid (CSF).

In addition to demonstrating a reduction in mutant huntingtin protein, WVE-120102 was
generally safe and well-tolerated across all patients, so we are exploring optimal dosing
and expect to add an additional treatment group to the ongoing Phase 1b/2a study at a
higher dose (32 mg) in January to evaluate effects on mutant huntingtin protein. We are
also adding an additional treatment group to our other Phase 1b/2a study called
PRECISION-HD1, evaluating the investigational therapy WVE-120101 targeting SNP1. We
now expect to share results from both studies including the 32 mg doses in the second half
of 2020.

We are deeply committed to the HD community. In addition to the PRECISION-HD studies,
we are developing other potential treatments for the disease, advancing the understanding
of wild-type huntingtin preservation, and supporting the needs of people living with HD.
All of us at Wave are enormously grateful to the PRECISION-HD clinical trial participants
and their families. We recognize the personal sacrifices made by each-and-every family
involved in these trials. Their participation along with the support of the entire HD
community are critical to advancing the scientific and medical understanding required to
defeat this devastating disease.

Michael Panzara, MD, MPH
Chief Medical Officer