# Genetic and epigenetic mechamisms of FSHD pathogenesis

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA-IRVINE · 2020 · $446,477

## Abstract

Facioscapulohumeral dystrophy (FSHD) is one of the most prevalent muscular dystrophies. The majority of
cases are associated with shortening of the D4Z4 repeat sequences on chromosome 4q (FSHD1) while
mutations in the SMCHD1 transcriptional repressor gene are linked to a minor subset of FSHD patients
(FSHD2). Mutations in SMCHD1 also greatly exacerbate the phenotype of FSHD1, thus acting as a modifier of
the disorder's severity in FSHD1. Abnormal expression of the DUX4 gene present in the D4Z4 repeats is
linked to the development of both FSHD1 and FSHD2. However, only a small percentage of patient muscle
cells express DUX4 protein, which can also occasionally be observed in muscle cells from unaffected
individuals. This suggests that DUX4 expression alone may not be sufficient for FSHD development.
Furthermore, exactly how the DUX4 gene is upregulated only in a small number of patient muscle cells and
how it contributes to FSHD development and progression are unclear. SMCHD1 is part of the histone H3
lysine 9-trimethylated (H3K9me3) “heterochromatin” structure that normally represses DUX4 expression, which
is compromised in both FSHD1 and FSHD2 patient cells. We obtained evidence that H3K9me3 is specifically
reduced not only at D4Z4 but also at other parts of the genome in FSHD cells. Furthermore, SMCHD1
mutations may have DUX4-independent effects on FSHD pathogenesis. Since D4Z4 repeats are not present
in the mouse genome, patient muscle cells are essential for assessing FSHD-specific cellular changes.
However, high-quality patient myoblasts are limited, and variability among samples with only a small subset of
cells expressing DUX4 may exacerbate the averaging artifact of population analysis. We plan to take two
complementary strategies to circumvent these issues and test our hypothesis: (1) development of clonal
FSHD-modeling human myoblast lines, and (2) single-nucleus profiling of primary control and FSHD muscle
cells. We propose a hypothesis that FSHD is a heterochromatin abnormality disorder, in which genome-wide
changes of H3K9me3 and SMCHD1 function predispose to or initiate FSHD, and a small number of (DUX4-
expressing) disease-driving cells dictate the progression of the phenotype. The Specific Aims of this project
are (1) to generate “FSHD-modeling” human myoblast lines to establish the FSHD disorder mechanism(s) and
to study D4Z4 chromatin regulation, (2) to perform genome-wide epigenetic and expression analyses at the
single-nucleus level to understand the consequences of DUX4 upregulation and possibly identify FSHD-driving
cells, and (3) to take a proteomics approach to identify the components of D4Z4 heterochromatic structure to
further delineate the mechanism and consequence of its dysregulation in FSHD, which will be integrated into
the analyses in Aims 1 and 2. The successful outcome of this project may lead to further understanding of the
mechanism(s) underlying FSHD pathogenesis and the identification of potential new therape...

## Key facts

- **NIH application ID:** 10000046
- **Project number:** 5R01AR071287-04
- **Recipient organization:** UNIVERSITY OF CALIFORNIA-IRVINE
- **Principal Investigator:** Seyed Ali Mortazavi
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $446,477
- **Award type:** 5
- **Project period:** 2017-09-01 → 2022-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10000046

## Citation

> US National Institutes of Health, RePORTER application 10000046, Genetic and epigenetic mechamisms of FSHD pathogenesis (5R01AR071287-04). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10000046. Licensed CC0.

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