Exome Chip Analysis Identifies Low-Frequency and Rare Variants in
MRPL38
for White Matter Hyperintensities on Brain Magnetic Resonance Imaging
Authors: Jian Xueqiu , Satizabal Claudia L. , Smith Albert V. , Wittfeld Katharina , Bis Joshua C. , Smith Jennifer A. , Hsu Fang-Chi , Nho Kwangsik , Hofer Edith , Hagenaars Saskia P. , Nyquist Paul A. , Mishra Aniket , Adams Hieab H.H. , Li Shuo , Teumer Alexander , Zhao Wei , Freedman Barry I. , Saba Yasaman , Yanek Lisa R. , Chauhan Ganesh , van Buchem Mark A. , Cushman Mary , Royle Natalie A. , Bryan R. Nick , Niessen Wiro J. , Windham Beverly G. , DeStefano Anita L. , Habes Mohamad , Heckbert Susan R. , Palmer Nicholette D. , Lewis Cora E. , Eiriksdottir Gudny , Maillard Pauline , Mathias Rasika A. , Homuth Georg , Valdés-Hernández Maria del C. , Divers Jasmin , Beiser Alexa S. , Langner Sönke , Rice Kenneth M. , Bastin Mark E. , Yang Qiong , Maldjian Joseph A. , Starr John M. , Sidney Stephen , Risacher Shannon L. , Uitterlinden André G. , Gudnason Vilmundur G. , Nauck Matthias , Rotter Jerome I. , Schreiner Pamela J. , Boerwinkle Eric , van Duijn Cornelia M. , Mazoyer Bernard , von Sarnowski Bettina , Gottesman Rebecca F. , Levy Daniel , Sigurdsson Sigurdur , Vernooij Meike W. , Turner Stephen T. , Schmidt Reinhold , Wardlaw Joanna M. , Psaty Bruce M. , Mosley Thomas H. , DeCarli Charles S. , Saykin Andrew J. , Bowden Donald W. , Becker Diane M. , Deary Ian J. , Schmidt Helena , Kardia Sharon L.R. , Ikram M. Arfan , Debette Stéphanie , Grabe Hans J. , Longstreth W.T. , Seshadri Sudha , Launer Lenore J. , Fornage Myriam ,   for the neuroCHARGE Working Group
Published: July 2018

Background and Purpose—
White matter hyperintensities (WMH) on brain magnetic resonance imaging are typical signs of cerebral small vessel disease and may indicate various preclinical, age-related neurological disorders, such as stroke. Though WMH are highly heritable, known common variants explain a small proportion of the WMH variance. The contribution of low-frequency/rare coding variants to WMH burden has not been explored.

Methods—
In the discovery sample we recruited 20 719 stroke/dementia-free adults from 13 population-based cohort studies within the Cohorts for Heart and Aging Research in Genomic Epidemiology consortium, among which 17 790 were of European ancestry and 2929 of African ancestry. We genotyped these participants at ≈250 000 mostly exonic variants with Illumina HumanExome BeadChip arrays. We performed ethnicity-specific linear regression on rank-normalized WMH in each study separately, which were then combined in meta-analyses to test for association with single variants and genes aggregating the effects of putatively functional low-frequency/rare variants. We then sought replication of the top findings in 1192 adults (European ancestry) with whole exome/genome sequencing data from 2 independent studies.

Results—

At 17q25, we confirmed the association of multiple common variants in
TRIM65
,
FBF1
, and
ACOX1
(
P
<6×10
−7
). We also identified a novel association with 2 low-frequency nonsynonymous variants in
MRPL38
(lead, rs34136221;
P
EA
=4.5×10
−8
) partially independent of known common signal (
P
EA(conditional)
=1.4×10
−3
). We further identified a locus at 2q33 containing common variants in
NBEAL1
,
CARF
, and
WDR12
(lead, rs2351524;
P
all
=1.9×10
−10
). Although our novel findings were not replicated because of limited power and possible differences in study design, meta-analysis of the discovery and replication samples yielded stronger association for the 2 low-frequency
MRPL38
variants (
P
rs34136221
=2.8×10
−8
).

Conclusions—
Both common and low-frequency/rare functional variants influence WMH. Larger replication and experimental follow-up are essential to confirm our findings and uncover the biological causal mechanisms of age-related WMH.