Early detection of Angelman syndrome resulting from de novo paternal isodisomic 15q UPD and review of comparable cases

Abstract

Angelman syndrome is a rare neurogenetic disorder that results in intellectual and developmental disturbances, seizures, jerky movements and frequent smiling. Angelman syndrome is caused by two genetic disturbances: either genes on the maternally inherited chromosome 15 are deleted or inactivated or two paternal copies of the corresponding genes are inherited (paternal uniparental disomy). A 16-month-old child was referred with minor facial anomalies, neurodevelopmental delay and speech impairment. The clinical symptoms suggested angelman syndrome. The aim of our study was to elucidate the genetic background of this case.
This study reports the earliest diagnosed angelman syndrome in a 16-month-old Hungarian child. Cytogenetic results suggested a de novo Robertsonian-like translocation involving both q arms of chromosome 15: 45,XY,der(15;15)(q10;q10). Molecular genetic studies with polymorphic short tandem repeat markers of the fibrillin-1 gene, located in the 15q21.1, revealed that both arms of the translocated chromosome were derived from a single paternal chromosome 15 (isodisomy) and led to the diagnosis of angelman syndrome caused by paternal uniparental disomy.
AS resulting from paternal uniparental disomy caused by de novo balanced translocation t(15q;15q) of a single paternal chromosome has been reported by other groups. This paper reviews 19 previously published comparable cases of the literature. Our paper contributes to the deeper understanding of the phenotype-genotype correlation in angelman syndrome for non-deletion subclasses and suggests that patients with uniparental disomy have milder symptoms and higher BMI than the ones with other underlying genetic abnormalities.

Full text

C A S E R E P O R T Open Access
Early detection of Angelman syndrome resulting
from de novo paternal isodisomic 15q UPD and
review of comparable cases
Emese Horváth
1*
, Zsuzsanna Horváth
1
, Dóra Isaszegi
1
, Gyurgyinka Gergev
2
, Nikoletta Nagy
1,3
, János Szabó
1
,
László Sztriha
2
, Márta Széll
1,3
and Emőke Endreffy
2
Abstract
Background: Angelman syndrome is a rare neurogenetic disorder that results in intellectual and developmental
disturbances, seizures, jerky movements and frequent smiling. Angelman syndrome is caused by two genetic
disturbances: either genes on the maternally inherited chromosome 15 are deleted or inactivated or two paternal
copies of the corresponding genes are inherited (paternal uniparental disomy). A 16-month-old child was referred
with minor facial anomalies, neurodevelopmental delay and speech impairment. The clinical symptoms suggested
angelman syndrome. The aim of our study was to elucidate the genetic background of this case.
Results: This study reports the earliest diagnosed angelman syndrome in a 16-month-old Hungarian child.
Cytogenetic results suggested a de novo Robertsonian-like translocation involving both q arms of chromosome 15:
45,XY,der(15;15)(q10;q10). Molecular genetic studies with polymorphic short tandem repeat markers of the fibrillin-1
gene, located in the 15q21.1, revealed that both arms of the translocated chromosome were derived from a single
paternal chromosome 15 (isodisomy) and led to the diagnosis of angelman syndrome caused by paternal
uniparental disomy.
Conclusions: AS resulting from paternal uniparental disomy caused by de novo balanced translocation t(15q;15q) of
a single paternal chromosome has been reported by other groups. This paper reviews 19 previously published
comparable cases of the literature. Our paper contributes to the deeper understanding of the phenotype-genotype
correlation in angelman syndrome for non-deletion subclasses and suggests that patients with uniparental disomy
have milder symptoms and higher BMI than the ones with other underlying genetic abnormalities.
Keywords: Angelman syndrome, Isodisomic 15, Uniparental disomy, Balanced translocation chromosome 15q
Background
Angelman syndrome (AS; OMIM 105830) is a rare neuro-
developmental disorder characterized by severe mental
and physical delay, limited speech, fine tremor, ataxia, ex-
cessive mouthing behavior, fascination with water, jerky
limb movements, seizures, craniofacial abnormalities and
unusually happy sociable behavior characterized by fre-
quent episodes of inappropriate smiling [1,2].
Seventy percent of AS cases investigated with molecular
genetics methods are the result of a small deletion in the
11–13 region of the maternal chromosome 15. A deletion
in the same region of the paternal chromosome 15 results
in the sister disorder Prader-Willi syndrome (PWS). Ex-
pression of the genes in the 11–13 region is regulated by
the PWS/AS imprinting center (IC), which differentially
silences the paternal copy of the ubiquitin protein
ligaseE3A (UBE3A) gene in the hippocampus and in the
cerebellum. Other genetic abnormalities resulting in AS
reported include uniparental disomy (UPD; 5%), muta-
tions of the IC (5%), mutations of the UBE3A gene (10%),
and other mechanisms (10%) [3,4].
In this paper, we report a 16-month-old Hungarian
child, who was referred to our genetic counseling unit
with delayed psychomotor and speech development and
* Correspondence: horvath.emese@med.u-szeged.hu
1
Department of Medical Genetics, University of Szeged, 4 Somogyi B. utca,
H-6720, Szeged, Hungary
Full list of author information is available at the end of the article
© 2013 Horváth et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Horváth et al. Molecular Cytogenetics 2013, 6:35
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dysmorphic features, including wide nasal bridge, low
set ears, thick lips, wide mouth with protuberant tongue
(Figure 1). Tongue thrusts were observed. Head circum-
ference was 47 cm (25 percentile). The affected child
was born at term after an uneventful first pregnancy
with normal weight (3260 g) and head circumference
(33 cm). The Apgar scores were 9, 10 and 10 at 1, 5 and
10 minutes, respectively. No signs of decreased fetal
movement, neonatal hypotonia or feeding difficulties
were reported. The clinical phenotype of the patient
suggested AS, therefore molecular cytogenetic investi-
gations were carried out to elucidate the genetic back-
ground of the presented case.
Results
Cytogenetic analysis demonstrated a 45,XY,der(15;15)
(q10;q10) karyotype in all analyzed cells from the index
patient (III/1, Figure 2). All metaphase cells displayed 45
chromosomes, suggesting a balanced homologous re-
arrangement of the long arms of chromosomes 15. The
parent’s karyotype was found to be normal, indicating a
de novo chromosome rearrangement in the patient.
Analysis of polymorphic short tandem repeat (STR)
markers of the fibrillin-1 gene, which is located in
15q21.1, revealed that both long arms of the aberrant
chromosome 15 were inherited from the father (Figure 3),
allowing a diagnosis of AS caused by paternal UPD. The
patient was homozygous at all loci for which his father
was heterozygous, indicating that the rearrangement
resulted from an isodisomic 15q.
Discussion
Cytological and molecular genetic investigation revealed
UPD suggesting a Robertsonian-like translocation 45,XY,
der(15;15)(q10;q10), a rearrangement of the acrocentric
chromosomes. Robertsonian translocations mostly form
de novo due to intrinsic properties of the acrocentric
chromosomes, which are likely to be the results of the
high homology between the short arm DNA sequences
of them [5]. A similar balanced 15;15 translocation
resulting from paternal UPD in AS were reported by
Freeman et al. (1993) [6], by Tonk et al. (1996) [7], by
Ramsden et al. (1996) [8], by Guitart et al. (1997) [9],
by Fridman et al. (1998) [10] and by Robinson et al.
(2000) [11].
Results from polymorphic STR marker analysis for the
fibrillin-1 gene, located in 15q21.1, indicated that both
arms of the aberrant chromosome 15 were inherited
from the father, allowing a diagnosis of AS caused by pa-
ternal UPD. DNA polymorphic markers demonstrated
that the patient was homozygous at all loci for which the
father was heterozygous, suggesting that the structural re-
arrangement was an isodisomic 15q and not a Robertsonian
translocation. Similar cases of AS resulting from isodisomic
15q associated UPD have already been demonstrated by
Freeman et al. (1993) [6] and by Robinson et al. (2000)
[11], however, the majority of the previously reported pater-
nal UPD associated AS cases were heterodisomic [7-10].
The severity of AS symptoms varies significantly.
Bottani et al. (1994) were the first, who reported that
the phenotype of AS with paternal isochromosome 15 is
milder than those caused by other mechanisms [12].
This observation was confirmed by Tonk et al. (1996)
[7], Smith et al. (1997) [13], Fridman et al. (1998) [10]
and Moncla et al. (1999) [14], however Prassad et al.
(1997) [15] have not observed differences between dele-
tion and UPD, moreover Poyatos et al. (2002) described
an even more severe phenotype [3]. The mildest symp-
toms have been reported for mutations of the UBE3A
gene [2,12,14,16], whereas the most severe symptoms
are reported for large deletions on chromosome 15
[2,14,16]. Varela et al. (2004) suggested that AS patients
with UPD may remain undiagnosed because of their
milder or less typical phenotype, leading to an overall
under-diagnosis of the disease (Table 1) [17,18]. Ac-
cording to Tan et al. (2011) [4], 46% of AS children with
UPD/imprinting defect showed significantly higher body
mass index (BMI) than the ones carrying deletions.
In the investigated patient, we observed dysmorphic fea-
tures, developmental delay, speech impairment and sleep
disturbances, excessive mouthing behavior, short attention
span, hand flapping, fascinating with water, and characte-
ristic EEG and MRI results. The clinical features of our pa-
tient are similar to previously published results [4,7,9,12].
The patient's AS symptoms are relatively mild, which
correlates well with the previous observations that AS pa-
tients with UPD usually have less severe clinical symptoms
[8,10,11,13]. The BMI of our patients was > 85%, which
correlated well with the previous results of Tan et al.
Figure 1 Clinical features of a patient with Angelman
syndrome resulting from de novo paternal isochromosome 15q
UPD. The dysmorphic symptoms of the 16 month old child include
wide nasal bridge, low set ears, thick lips, wide mouth and
protruding tongue.
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Figure 2 The karyotype of the AS patient. The cytogenetic image displays 45 metaphase chromosomes with an apparently balanced
homologous rearrangement between the long arms of chromosomes 15. Cytogenetic result: 45,XY der(15;15)(q10;q10).
Figure 3 Genetic analysis of the affected family using polymorphic STR markers MMTS2, D15S119 and D15S1028 for the fibrillin-1
gene. Marker analysis of the patient (III/1), his parents (II/1, II/2), maternal aunts (II/3, II/4, II/5), maternal grandparents (I/3, I/4), and paternal
grandparents (I/1, I/2) was performed by ALFexpress gel electrophoresis. The patient is homozygous for polymorphisms occurring in the father
but not the mother, indicating that both arms of the aberrant chromosome 15 were of paternal origin.
Horváth et al. Molecular Cytogenetics 2013, 6:35 Page 3 of 5
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(2011) [4] and further confirmed that AS patients with
UPD have significantly higher BMI than AS patients with
other underlying genetic abnormalities.
The patient was diagnosed with AS at the age of 16
months, earlier than in previous reports of UPD,
allowing the parents to be given a correct prognosis and
an explanation of delayed neurological developmental
as well as the possibility of early interventional therapy.
In addition, the parents were counseled that the child is
at risk for obesity and its associated complications,
which could be managed with lifestyle adjustments. As
the aberration was the result of a de novo occurrence,
the parents were not counseled on the risk of recur-
rence for further pregnancies.
Conclusions
In this paper we report the case of a 16-month-old
Hungarian boy affected by AS due to UPD. The early
diagnosis of AS has great significance, it allows the pa-
rents to be given a correct prognosis and the possibility
of early interventional therapy. The detection of UPD
and reviewing the previous cases reported in the litera-
ture have also pivotal role, since it contributes to the
deeper understanding of the phenotype-genotype cor-
relation in AS for non-deletion subclasses. Our data
suggest that AS patients with UPD have milder symp-
toms and higher BMI than AS patients with other
underlying genetic abnormalities.
Methods
Cytogenetic analysis of the child and his parents was
carried out with standard methods using G banding with
the Cytovision imaging system. The results of the cyto-
genetic studies suggested UPD, and, therefore, further
molecular genetic studies were carried out. Genomic
DNA was extracted from venous blood of the index
patient (III/1), his parents (II/1, II/2), his grandparents
(I/1, I/2, I/3, I/4) and his maternal aunts (II/3, II/4, II/5)
[19]. Chromosome 15 segregation analysis with intra-
genic and extragenic markers for the fibrillin-1 gene was
performed for all family members using amplified frag-
ment length polymorphism analysis on an ALFexpress
instrument [20]. To determine the molecular back-
ground and the recurrence risk, primers for the follo-
wing microsatellite markers were used in the analysis:
D15S119, D15S1028 and MMTS2.
Consent
Written informed consent was obtained from the pa-
tient’s legal guardian for publication of this case report
and accompanying images. A copy of the written con-
sent is available for review by the Editor-in-Chief of this
journal.
Abbreviations
AS: Angelman syndrome; PWS: Prader-Willi syndrome; IC: Imprinting center;
UBE3A: Ubiquitin protein ligaseE3A gene; UPD: Uniparental disomy;
STR: Short tandem repeat; BMI: Body mass index.
Competing interests
The authors declare that they have no competing interest.
Authors’contribution
EH contributed to data collection and the first draft of the manuscript. ZH, DI
and NN carried out the mutation analysis. GG and JS cared for the patient.
LS, MS and EE were mentors who contributed equally to this work. All
authors read and approved the final manuscript.
Table 1 The clinical features of the patient, in order of
frequency, compared to the 13 AS patients with UPD/
imprinting defects reported by Tan [4]
The analyzed
parameters at
diagnosis
Values for the
patient described in
this report
Values for the 13 AS
patients with UPD/
imprinting defects
reported by Tan [4]
Age (months) at
diagnosis
0–24 1 0
25–36 - 5
37–60 - 8
Gender M 8M/5F
Short attention
span
+ 12/13 (92%)
History of sleep
difficulties
+ 12/13 (92%)
Normal tone at
evaluation
+ 12/13 (92%)
Mouthing
behavior
+ 11/13 (85%)
Hand flapping + 11/13 (85%)
Drooling + 10/13 (77%)
Feeding
difficulties in
infancy
- 10/13 (77%)
Ataxic or broad
based gait
- 8/11 (73%)
Gastro-esophageal
reflux
- 9/13 (69%)
Widely spaced
teeth
+ 9/13 (69%)
Fascination with
water
+ 8/13 (62%)
Easily provoked
laughter
+ 8/13 (62%)
Clinical seizures - 6/13 (46%)
BMI>85% + 6/13 (46%)
Unusually light
hair or skin color
- 3/13 (23%)
Prognathism - 3/13 (23%)
Mid-face
hypoplasia
- 2/13 (15%)
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Acknowledgments
TÁMOP-4.2.2.A-11/1/KONV-2012-0035 grant, TÁMOP-4.2.2/B-10/1/KONV-2010-
0012 grant. Dr. László Sztriha received funds from the Marie Curie
International Reintegration Grant (MIRG-CT-2005-030967) within the 6th
European Community Framework Program. OTKA PD104782 2012–2015
grant, Nikoletta Nagy is supported by Janos Bolyai Scholarship 2011–2014.
Author details
1
Department of Medical Genetics, University of Szeged, 4 Somogyi B. utca,
H-6720, Szeged, Hungary.
2
Department of Pediatrics and Child Health Centre,
University of Szeged, Szeged, Hungary.
3
Dermatological Research Group of
the Hungarian Academy of Sciences, University of Szeged, Szeged, Hungary.
Received: 9 July 2013 Accepted: 10 August 2013
Published: 8 September 2013
References
1. Clayton-Smith J, Laan L: Angelman syndrome: a review of the clinical and
genetic aspects. J Med Genet 2003, 40:87–95.
2. Williams CA, Beaudet AL, Clayton-Smith J, Knoll JH, Kyllerman M, Laan LA,
Magenis RE, Moncla A, Schinzel AA, Summers JA, Wagstaff J: Angelman
syndrome 2005: updated consensus for diagnostic criteria. Am J Med
Genet 2006, 140:413–418.
3. Poyatos D, Guitart M, Gabau E, Brun C, Mila M, Vaquerizo J, MD C: Severe
phenotype in Angelman syndrome resulting from paternal
isochromosome 15. J Med Genet 2002, 39:4.
4. Tan WH, Bacino CA, Skinner SA, Anselm I, Barbieri-Welge R, Bauer-Carlin A,
Beaudet AL, Bichell TJ, Gentile JK, Glaze DG, Horowitz LT, Kothare SV,
Lee HS, Nespeca MP, Peters SU, Sahoo T, Sarco D, Waisbren SE, Bird LM:
Angelman syndrome: mutations influence features in early childhood.
Am J Med Genet 2011, 155:81–90.
5. Kim SR, Shaffer LG: Robertsonian translocations: mechanisms of
formation, aneuploidy, and uniparental disomy and diagnostic
considerations. Genet Test 2002, 6:163–168.
6. Freeman SB, May KM, Pettay D, Fernhoff PM, Hassold TJ: Paternal
uniparentaldisomy in a child with a balanced 15;15 translocation and
Angelman syndrome. Am J Med Genet 1993, 45:625–630.
7. Tonk V, Schultz RA, Christian SL, Kubota T, Ledbetter DH, Wilson GN:
Robertsonian (15q,15q) translocation in a child with Angelman syndrome:
evidence of uniparentaldisomy. Am J Med Genet 1996, 66:426–428.
8. Ramsden S, Gaunt L, Seres-Santamaria A, Clayton-Smith J: A case of
Angelman syndrome arising as a result of a de novo Robertsonian
translocation. Acta Genet Med Gemellol 1996, 45:255–261.
9. Guitart M, Escudero T, Gabau E, Dorminguez MC, Jimenez MD, Mila M, Coll MD:
Two new cases of Angelman syndrome with a balanced 15;15 translocation
and paternal uniparental disomy. Cytogenet Cell Genet 1997, 77:227.
10. Fridman C, Varela MC, Nicholls RD, Koiffmann CP: Unusual clinical features
in an Angelman syndrome patient with uniparental disomy due to a
translocation 15q15q. Clin Genet 1998, 54:303–308.
11. Robinson WP, Christian SL, Kuchinka BD, Peñaherrera MS, Das S,
Schuffenhauer S, Malcolm S, Schinzel AA, Hassold TJ, Ledbetter DH: Somatic
segregation errors predominantly contribute to the gain or loss of a
paternal chromosome leading to uniparental disomy for chromosome
15. Clin Genet 2000, 57:349–358.
12. Bottani A, Robinson WP, DeLozier-Blanchet CD, Engel E, Morris MA,
Schmitt B, Thun-Hohenstein L, Schinzel A: Angelman syndrome due to
paternal uniparentaldisomy of chromosome 15: milder phenotype? Am J
Med Genet 1994, 51:35–40.
13. Smith A, Marks R, Haan E, Dixon J, Trent RJ: Clinical features in 4 patients
with Angelman syndrome resulting from paternal uniparental disomy.
J Med Genet 1997, 34:426–429.
14. Moncla A, Malzac P, Voelckel MA, Auquier P, Girardot L, Mattei MG, Philip N,
Mattei JF, Lalande M, Livet MO: Phenotype-genotype correlation in 20
deletion and non-deletion Angelman syndrome patients. Eur J Hum
Genet 1999, 7:131–139.
15. Prasad C, Wagstaff J: Genotype and phenotype in Angelman syndrome
caused by paternal UPD 15. Am J Med Genet 1997, 70:328–329.
16. Liehr T: Cases with uniparental disomy. http://www.fish.uniklinikum-jena.de/
UPD.html. [accessed 05/08/2013].
17. Lossie AC, Whitney MM, Amidon D: Distinct phenotypes distinguish the
molecular classes of Angelman syndrome. J Med Genet 2001, 38:834–845.
18. Varela MC, Kok F, Otto PA, Koiffmann CP: Phenotypic variability in
Angelman syndrome: comparison among different deletion classes and
between deletion and UPD subjects. Eur J Hum Genet 2004, 12:987–992.
19. Abrams DJ, Aronoff AR, Ann Berend S, Roa BB, Shaffer LG, Geier MR:
Prenatal diagnosis of a homologous Robertsonian translocation
involving chromosome 15. Prenat Diagn 2011, 21:676–679.
20. Judge DP, Biery NJ, Dietz HC: Characterization of microsatellite markers
flanking FBN1: utility in the diagnostic evaluation for Marfan syndrome.
Am J Med Genet 2001, 99:39–47.
doi:10.1186/1755-8166-6-35
Cite this article as: Horváth et al.:Early detection of Angelman
syndrome resulting from de novo paternal isodisomic 15q UPD and
review of comparable cases. Molecular Cytogenetics 2013 6:35.
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