Mild form of Danon disease: two case reports

Mild form of Danon disease: two case reportsMild form of Danon disease: two case reports
Toshio Yasui a , b , Utako Nagaoka
a , Yasushi Oya
c , Akinori Uruha
a , Shiro Matsubara
a , Keizo Sugaya
f , Mariko Okubo
f , Kazuma Sugie
g , Ichizo Nishino
a Department of Neurology, Tokyo Metropolitan Neurological Hospital, Tokyo, Japan b Department of Neurology, National Hospital Organization Tokyo Medical Center, Tokyo, Japan
c Department of Neurology, National Center Hospital, National Center of Neurology and Psychiatry, Tokyo, Japan d Department of Neuropathology, Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Berlin,
Germany e Department of Cardiology, Tokyo Metropolitan Hiroo Hospital, Tokyo, Japan
f Department of Neuromuscular Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan g Department of Neurology, Nara Medical University, Nara, Japan
Received 19 September 2020; received in revised form 15 July 2021; accepted 19 July 2021
Abstract
Danon disease is typically lethal by the mid-twenties in male patients due to cardiomyopathy. This report aims to describe two unrelated male patients showing mild manifestations of the disease. A 39-year-old man presented with a 10-year history of elevated serum creatine kinase levels with slowly progressive muscle weakness. Muscle pathology showed autophagic vacuoles with sarcolemmal features. Genetic testing revealed a hemizygous mutation in exon 9b, an alternatively spliced exon, of lysosome-associated membrane protein-2 ( LAMP-2 ) (c.1097_1098delAA). Cardiac testing showed asymptomatic mild left ventricular hypertrophy. He had borderline intelligence. Early stage of retinopathy was detected. Another male patient, currently 53-year-old, had asymptomatic supraventricular extrasystole and muscle weakness but no intellectual disability, harboring the same mutation. He also had retinopathy. The present patients commonly carry a mutation in exon 9b of LAMP-2 , suggesting that mutations in the exon are associated with a mild form of Danon disease. © 2021 Elsevier B.V. All rights reserved.
Keywords: Lysosome-associated membrane protein-2 ( LAMP-2 ); Alternative splicing; Autophagic vacuolar myopathy; Cardiomyopathy; Genotype-phenotype correlation; Autophagy.
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. Introduction
Danon disease (OMIM: 300257) is an X-linked dominant ysosomal storage disease characterized by the triad of ardiomyopathy, myopathy, and mental retardation [1] . The ausative gene is lysosome-associated membrane protein-2
LAMP-2 ), which plays an important role in autophagosome- ysosome fusion in autophagy [2] . Typically, cardiomyopathy
s remarkably severe in male patients, requiring heart ransplantation; otherwise, it is lethal by their mid-twenties
∗ Corresponding author at: Department of Neurology, Tokyo Metropolitan eurological Hospital, 2-6-1, Musashidai, Fuchu, Tokyo 183-0042, Japan.
E-mail address: [email protected] (A. Uruha).
a ( H t F
ttps://doi.org/10.1016/j.nmd.2021.07.017 960-8966/© 2021 Elsevier B.V. All rights reserved.
1 , 3 , 4] . We herein report two unrelated male patients showing
ild manifestations of Danon disease.
. Case reports
The male Japanese patient, currently 39 years old, visited
local clinic for a suspicion of a liver disease due to
erum transaminase elevation in a medical checkup at the ge of 26 years, and then a high serum creatine kinase CK) level was found (2032 U/L, normal range 30–150 U/L). e was referred to our neurology department and found
o have gait abnormality due to leg muscles weakness. urther work-up was recommended, but he ceased to come
T. Yasui, U. Nagaoka, Y. Oya et al. Neuromuscular Disorders 31 (2021) 1207–1211
t w d a i s o y e n C 3 S T R d s N E n i w h a m 7 h w ( g b a h o f d n a e
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o our hospital outpatient clinic because subjective symptoms ere tolerable for him. Apparently his motor and mental evelopment was not particularly abnormal, although he was slower runner and worse at some sports than average n his childhood. He did not complain of any cardiac ymptom. Although he did not realize clear worsening
f symptoms, he came back to our hospital after 10
ears to clarify the cause of hyperCKemia. Neurological xamination showed moderate to marked weakness in his eck, truncal, and lower limb muscles: Medical Research
ouncil (MRC) grades 2 in the neck flexor muscles and
to 4 in the truncal and proximal lower limb muscles. tanding on his toes or heels were almost impossible. endon reflexes were not elicitable in the lower limbs. etrospectively, muscle weakness seemed to be gradually
eveloped since his early or mid-twenties. Laboratory tests howed an elevated serum CK level (1074 U/L) and a normal T-proBNP level (57 pg/ml, cut-off value < 125 pg/ml). lectrocardiogram (ECG) and 24-hour Holter ECG revealed
o significant changes. Echocardiogram showed 12 mm of nterventricular septum thickness and 12 mm of posterior all thickness, suggesting borderline of left ventricular ypertrophy, while ejection fraction was normal (70%). No
bnormality was detected in gadolinium-enhanced cardiac agnetic resonance imaging. Total intelligence quotient was
7 on Wechsler Adult Intelligence Scale-IV. Biopsy from
is left tibialis anterior muscle showed myopathic changes ith autophagic vacuoles with sarcolemmal features (AVSF)
Fig. 1 ) [5] . In immunohistochemistry for LAMP-2, the eneral expression was fainter compared to healthy control ut still positively stained in membrane of the vacuoles nd mildly in sarcolemma. Sanger sequencing revealed a emizygous mutation c.1097_1098delAA in exon 9b, one f the alternatively spliced exons, of LAMP-2 , resulting in
rameshift p.Q366Rfs ∗6 (NM_013995.2). Collectively, he was iagnosed as having Danon disease. Eye examination showed
o decrease of visual acuity but decreased retinal thickness nd negative electroretinogram, suggesting retinopathy with
arly stage retinitis pigmentosa. His mother, 64 years old, recently had palpitation due
o premature atrial contraction. Also, she was diagnosed as aving retinitis pigmentosa at the age of 30 years, which
aused low visual acuity since her late fifties. Her father, who
ied of brainstem hemorrhage at 69 years old, went blind due o retinitis pigmentosa in his fifties. Two younger brothers of he proband (38 and 34 years old, respectively) were healthy. here was no consanguinity in the family.
.2. Patient 2
p without any developmental abnormality, but he noticed
difficulty in sit-up exercise at the age of 14 years. ECG
bnormality was detected in a medical checkup around that ime. However, he did not have a regular examination due o lack of any symptom. While mild elevation of serum
ransaminase levels had been detected since his teenage years,
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iver investigation did not show any abnormality. At the age f 29 years, hyperCKemia was incidentally found (1585 U/L), nd he was referred to a neurology clinic. Neurological xamination showed a significant weakness of truncal muscles MRC grade 2) although normal, or mild weakness if any, n other muscles. There was no intellectual disability. In 24- our Holter ECG, asymptomatic supraventricular extrasystole as detected (3789 beats per day), which was not considered
athological at this moment. Echocardiography showed no
bnormality. Biopsy of left rectus femoris showed myopathic hanges with AVSF. A tentative diagnosis of Danon disease as made, although his symptoms were atypically mild,
acking obvious cardiac involvement or mental retardation. ater, at the age of 44 years, the diagnosis was confirmed
y a genetic test of LAMP-2 demonstrating a hemizygous utation c.1097_1098delAA in exon 9b. Cardiomyopathy
radually developed, and he complained palpitation and chest iscomfort; then administration of beta-blocker, bisoprolol, as initiated. When he was 49 years old, he noticed
entral visual field defect in his right eye, being diagnosed
ith retinitis pigmentosa. His left eye also showed mildly
ecreased retinal sensitivity. Recently, he developed difficulty
limbing upstairs due to muscle weakness. Intellectual aspects emains normal until now. There is a maternal family history
f similar symptoms in his male cousin and more mildly in
is female cousin and aunt; this family was included in a eport of Japanese national survey of Danon disease [4] . His arents, grandparents, and younger sister did not have any
imilar symptom. As far as we could trace, this family is not relative of the Patient 1. The clinical feature until 29 years ld was previously described [6] .
. Discussion
In a nationwide survey on Danon disease in Japan
ncluding 39 patients from 20 families, the average age f death was 19 ±5 years old in the male patients with
anon disease (all the death were associated with cardiac nvolvement) [4] . Other studies also showed that most of he male patients required heart transplantation or died by
heir mid-twenties [7] . In light of the data, phenotypes of he present patients are obviously milder, at least regarding
ardiac involvement and lethality. While insidious progression
akes onset points difficult to determine, the onset of the atient 1 in his twenties seems later compared to the onset ges ever reported (mostly by teenage years) [4 , 7] .
The patients commonly had a mutation in exon 9b
f LAMP-2 . Through our literature search, we identified
ve male patients carrying exon 9b mutations with precise linical description ( Table 1 ) [8 , 9 , 10] . The reported patients howed milder phenotypes than what is known as typical or male Danon disease (e.g. their ages at report were ixties or later in all the patients, apart from a 16- ear-old patient) although there were some phenotypic ariations. Exon 9 of LAMP-2 exists in three forms, xon 9a, 9b, and 9c, which are alternatively spliced and
roduce three protein isoforms, LAMP-2A, −2B, and −2C
T. Yasui, U. Nagaoka, Y. Oya et al. Neuromuscular Disorders 31 (2021) 1207–1211
Fig. 1. Muscle pathology of Patient 1. (A) Myofibers with basophilic granular structures (arrowhead) are observed besides those with vacuoles. Hematoxylin and eosin stain (H&E). (B, C) Vacuolar membranes express acetylcholine esterase and dystrophin, showing the nature of autophagic vacuoles with sarcolemmal features (autolysosomes surrounded by intracytoplasmic sarcolemma-like structure [Reference 5]). B: acetylcholine esterase stain (AChE). C: immunohistochemistry for dystrophin-1 (Dys). (D, E, F) Immunohistochemistry for LAMP-2 (H4B4, 1:1000 dilution, Developmental Studies Hybridoma Bank, Iowa, IA, USA) on the same slide. The stainability is fainter compared to healthy control (F) but still positive in membrane of the vacuoles and mildly in sarcolemma. LAMP-2 expression is completely undetectable in a non-exon 9b male patient’s sample (E). Scale bars: 20 μm in (B) and 50 μm in the others, respectively.
Table 1 Mild Danon disease patients carrying exon 9b mutations of LAMP-2 .
Patient 1 Patient 2 Ref 8 , 9 Ref 8 , 9 Ref 8 , 9 Ref 8 , 9 Ref 10
Onset age (years) 26 29 Childhood Teens NA 64 9 Age at report (years) 39 53 63 63 Later than 63 69 16 Mutation c.1097_1098
delAA
Truncal muscles Generalized. Wheelchair bound
Distal of legs Scapulohumeral, lower legs
Scapulohumeral, lower legs
Supraventricular extrasystole
SSS(pacemaker). LVH
Symptomatic pAf Normal NA First-degree AVB. Mildly decreased diastolic function
Intelligence Borderline Normal Normal Normal Normal NA Normal Eye Early retinopathy
suspected Retinitis pigmentosa
NA
CK (U/L) 1907 1585 > 2x normal > 2x normal > 2x normal > 2x normal 958
Abbreviations. AVB: atrioventricular block, CK: creatine kinase, ECG: electrocardiogram, LVH: left ventricular hypertrophy, NA: not available, pAf: paroxysmal atrial fibrillation, SSS: sick sinus syndrome.
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T. Yasui, U. Nagaoka, Y. Oya et al. Neuromuscular Disorders 31 (2021) 1207–1211
Table 2 Mild Danon disease patients with non-exon 9b mutations of LAMP-2 .
Ref 16 Ref 17 Ref 18 Ref 19
Onset age (years) 28 33 37 45 Age at report (years) 41 40 50 52 Mutation c.865–3C > A
Skipping of exon 7 (stop codon) c.65–2A > G
Four different transcripts c.52T > C
p.C18R
p.G93R
Region Intron 6 Intron 1 Exon 1 Exon 3 Skeletal muscle Upper arms, mild Normal Normal NA
Heart WPW. Complete AVB
High degree AVB. DCM
Intelligence NA Mild decline Normal NA
Eye NA NA NA NA
CK (U/L) 522 Up to 1100 404 Normal
Abbreviations. AVB: atrioventricular block, CK: creatine kinase, DCM: dilated cardiomyopathy, HCM: hypertrophic cardiomyopathy, NA: not available, WPW: Wolf-Parkinson-White syndrome.
[ t d u s c c a D w w d s p t e w w m t e h i 4 T s i m L m m [ f
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3 , 7] . These isoforms share N-terminal lumenal domain, but hey have different transmembrane domain and cytoplasmic omain at C terminus. While LAMP-2A and −2C express biquitously, LAMP-2B expresses mainly in cardiac and
keletal muscles and brain [2 , 7] . LAMP-2b knockout in
ardiomyocytes derived from human induced pluripotent stem
ells caused defects in autophagic fusion and functional bnormalities, recapitulating some of the phenotypes of anon disease cardiomyocytes [11] . This is consistent ith the fact that individuals with mutations in exon 9b, hich affect only LAMP-2B isoform, can manifest Danon
isease phenotype. Nevertheless, such patients commonly
how milder symptoms, which may be explained by the reservation of LAMP-2A and −2C that would compensate he deficiency of LAMP-2B to some extent. Indeed the xpression of LAMP-2 in the present patient’s muscle sample as reduced compared to healthy control but still present, hereas it was completely undetectable in clinically typical ale Danon disease due to non-exon 9b mutations. According
o a RNA-seq database of the Genotype-Tissue Expression, xon 9b is estimated to occupy 32–49% in left ventricle of eart and 85–87% in skeletal muscle (exon 9a is 40–64%
n left ventricle and 10–13% in skeletal muscle; exon 9c is –12% in left ventricle and 0–5% in skeletal muscle) [12] . he less predominance of exon 9b in heart compared with
keletal muscle may be linked to milder cardiac involvement n contrast to relatively conspicuous manifestation in skeletal uscles. On the other hand, a recent report showed that AMP-2b gene transfer to Lamp2 knockout mice improved
etabolic and physiologic function in the Danon disease urine model, suggesting LAMP-2B was functionally critical
13] . As this may be contradictory to what we described, urther investigation is needed.
Both of the patients and some of family members of he Patient 1, although not proven to carry the mutation, ad retinopathy. Retinopathy in Danon disease has been
ess frequently described [4 , 9 , 14 , 15] . Since LAMP-2 is xpressed only in retinal pigmented epithelium in eye, LAMP- deficiency is likely to cause loss of photoreceptors [7] .
J
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s the patients with exon 9b mutations survive longer than
hose with mutations in other sites, retinopathy may be ore likely to be manifest or detectable during their longer-
erm disease course. This might also be the reason why
he previous reports detected retinopathy more frequently
n female patients, whose symptoms are milder than male atients [14 , 15] . There may be a possibility of a specific ssociation with exon 9b mutations, but further investigation
ill be necessary to elucidate it. We found four reported patients with non-exon 9b
utations who were described as mild phenotypes or late nset ( Table 2 ) [16 , 17 , 18 , 19] . The mild phenotypes might e explained by production of a certain amount of mutant AMP-2 protein due to missense or splice site mutation. owever, compared with the patients with exon 9b mutations,
t least cardiomyopathy seemed more severe. We delineated the two patients with the mutation in exon
b of LAMP-2 showing milder phenotypes of Danon disease. hese cases, together with the previous reports, demonstrate
hat the disease severity is more variable than widely known
nd that exon 9b mutations, besides the mutations in other arts, are associated with the mild form.
thical approval
All the material used in this study was obtained for iagnostic purpose and permitted for scientific use with
ritten informed consent.
There is no conflict of interest provided for any others.
cknowledgement
This study was supported partly by Intramural Research
rant ( 2-5 and 29-4 ) for Neurological and Psychiatric isorders of NCNP and AMED under Grant Numbers
P20ek0109490h0001 and JP19ek0109285h0003 .
R
eference
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