? 2006 Wiley-Liss, Inc.American Journal of Medical Genetics 140A:413–418 (2006)
Angelman Syndrome 2005: Updated Consensus for
Charles A. Williams,1,2* Arthur L. Beaudet,2,3Jill Clayton-Smith,4Joan H. Knoll,5
Martin Kyllerman,6Laura A. Laan,7R. Ellen Magenis,8Ann Moncla,9Albert A. Schinzel,10
Jane A. Summers,11and Joseph Wagstaff2,12
1Department of Pediatrics, Division of Genetics, R.C. Philips Unit, University of Florida, Gainesville, Florida
2Scientific Advisory Committee, Angelman Syndrome Foundation, Aurora, Illinois
3Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas
4Academic Department of Medical Genetics, St. Mary’s Hospital, Manchester, United Kingdom
5Section of Medical Genetics and Molecular Medicine, Children’s Mercy Hospital and Clinics,
University of Missouri-Kansas City School of Medicine, Kansas City, Missouri
6Department of Neuropediatrics, The Queen Silvia Children’s Hospital, University of Goteborg, Goteborg, Sweden
7Department of Neurology, Leiden University Medical Center, RC Leiden, The Netherlands
8Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, Oregon
9De ´partement de Ge ´ne ´tique Me ´dicale, Ho ˆpital des enfants de la Timone, Marseille, France
10Institute of Medical Genetics, University of Zurich, Zurich, Switzerland
11McMaster Children’s Hospital, Hamilton Health Sciences, Hamilton, Ontario, Canada
12Department of Pediatrics, Clinical Genetics Program, Carolinas Medical Center, Charlotte, North Carolina
Received 19 September 2005; Accepted 2 October 2005
In 1995, a consensus statement was published for the
purpose of summarizing the salient clinical features of
Angelman syndrome (AS) to assist the clinician in making a
timely and accurate diagnosis. Considering the scientific
advances made in the last 10 years, it is necessary now
to review the validity of the original consensus criteria. As in
the original consensus project, the methodology used for
this review was to convene a group of scientists and
clinicians, with experience in AS, to develop a concise
consensus statement, supported by scientific publications
where appropriate. It is hoped that this revised consensus
document will facilitate further clinical study of individuals
with proven AS, and assist in the evaluation of those who
appear to have clinical features of AS but have normal
laboratory diagnostic testing. ? 2006 Wiley-Liss, Inc.
Key words: angelman
15q11.2-q13; paternal UPD; diagnosis; criteria; behavioral
In 1995, a consensus statement was published for
the purpose of summarizing the salient clinical
features of Angelman syndrome (AS) [Williams
et al., 1995]. Now, a decade later, it seems appro-
knowledgeabout the molecular andclinical features
of the syndrome. Like the first study, the methodol-
ogy used to update the revision was to convene
a group of scientists and clinicians, with experience
in AS, to develop a concise consensus statement,
supported by the scientific publications on AS. The
Scientific Advisory Committee of the U.S. AS Foun-
dation assisted in the selection of individuals who
were invited to contribute to this project.
As in the original consensus study, Tables I–III are
and diagnosis of AS, especially for those unfamiliar
with this clinical disorder. These criteria are applic-
critical region (deletion positive), paternal unipar-
ental disomy (UPD), imprinting defects (IDs), and
mutations in the ubiquitin-protein ligase E3A gene
Table I lists the developmental history and
laboratory findings expected for AS. There are only
minor changes when compared to the original 1995
*Correspondence to: Charles A. Williams, M.D., Department of
Pediatrics, Division of Genetics, P.O. Box 100296, Gainesville, FL
32610. E-mail: Willicx@peds.ulf.edu
table. Some comments should be noted regarding
the table’s notation that the prenatal history is
‘‘normal.’’ There is an association of UPD AS with
advanced maternal age presumably causing non-
subsequently ‘‘rescued’’ by conversion to paternal
UPD [Robinson et al., 1996, 2000]. While it does
appear that fetal development and prenatal studies
such as ultrasound and growth parameters remain
normal in AS, it has recently been discovered that
assisted reproductive technologies (ART), such as
in vitro fertilization (IVF) or intra-cytoplasmic sperm
due to the non-deletion type of IC defect [Cox et al.,
2002; Orstavik et al., 2003; Niemitz and Feinberg,
2004; Shiota and Yamada, 2005]. Another imprinting
defect disorder unrelated to AS, the Beckwith–
Wiedemann syndrome, has also been associated
with ART. A recent report as well notes that couples
who have had a prolonged time to pregnancy (i.e.,
beyond 2 years) may be over represented among AS
individuals who have a non-deletion type of ID
[Ludwig et al., 2005]. However, it is not yet known if
study is needed to determine this.
Table I has also been changed to indicate that
feeding problems may be present in the first 6
months of life. Questionnaire or clinical surveys
feeding-related problems [Zori et al., 1992; Smith
et al., 1996; Bird et al., 2005]. Many AS babies have
difficulty with breast or bottle feeding including
problems of apparent uncoordinated sucking, ton-
gue thrusting, and poor breast attachment. In later
infancy, gastroesophageal reflux can occur. Such
feeding abnormalities can also occur in other
neurological disorders so its presence is quite non-
specific regarding raising increased suspicion for the
TABLE I. 2005: Developmental History and Laboratory Findings
1. Normal prenatal and birth history with normal head
circumference and absence of major birth defects. Feeding
difficulties may be present in the neonate and infant
Developmental delay evident by 6–12 months of age,
sometimes associated with truncal hypotonus. Unsteady
limb movements and/or increased smiling may be evident
Delayed but forward progression of development (no loss of
Normal metabolic, hematologic, and chemical laboratory
Structurally normal brain using MRI or CT (may have mild
cortical atrophy or dysmyelination)
TABLE II. 2005: Clinical Features of AS
A. Consistent (100%)
Developmental delay, functionally severe
Movement or balance disorder, usually ataxia of gait, and/or tremulous movement of limbs. Movement disorder can be mild. May not
appear as frank ataxia but can be forward lurching, unsteadiness, clumsiness, or quick, jerky motions
Behavioral uniqueness: any combination of frequent laughter/smiling; apparent happy demeanor; easily excitable personality, often with
uplifted hand-flapping, or waving movements; hypermotoric behavior
Speech impairment, none or minimal use of words; receptive and non-verbal communication skills higher than verbal ones
B. Frequent (more than 80%)
Delayed, disproportionate growth in head circumference, usually resulting in microcephaly (?2 SD of normal OFC) by age 2 years.
Microcephaly is more pronounced in those with 15q11.2-q13 deletions
Seizures, onset usually <3 years of age. Seizure severity usually decreases with age but the seizure disorder lasts throughout adulthood
Abnormal EEG, with a characteristic pattern, as mentioned in the text. The EEG abnormalities can occur in the first 2 years of life and can
precede clinical features, and are often not correlated to clinical seizure events
C. Associated (20%–80%)
Tongue thrusting; suck/swallowing disorders
Feeding problems and/or truncal hypotonia during infancy
Wide mouth, wide-spaced teeth
Excessive chewing/mouthing behaviors
Hypopigmented skin, light hair, and eye color compared to family), seen only in deletion cases
Hyperactive lower extremity deep tendon reflexes
Uplifted, flexed arm position especially during ambulation
Wide-based gait with pronated or valgus-positioned ankles
Increased sensitivity to heat
Abnormal sleep-wake cycles and diminished need for sleep
Attraction to/fascination with water; fascination with crinkly items such as certain papers and plastics
Abnormal food related behaviors
Obesity (in the older child)
WILLIAMS ET AL.
American Journal of Medical Genetics: DOI 10.1002/ajmg.a
diagnosis of AS. Truncal hypotonia may also be
evident during the first 6–12 months of life, and in
emotionally released, tension increase in the mus-
cles, more evident in the lower than in the upper
Otherwise, experience over the last 10 years has
generally supported observations that early AS
growth parameters are normal and that AS children
lack any significant malformations or biochemical/
metabolic test abnormalities. Individual case reports
have reported isolated brain malformations [Van
Lierde et al., 1990; Incorpora et al., 1994; Mas-
troyianni and Kontopoulos, 2002; Meyer Witte et al.,
2005] or other types of physical and neurological
problems [Douchin et al., 2000; Harbord, 2001;
Stecker and Myers, 2003; Deda et al., 2004; Katzos
et al., 2004; Oiglane-Shlik et al., 2005], but these
appear to be isolated reports that may be coinciden-
tal occurrences. The brain MRI description from the
first consensus study appears to be still valid as
the AS brain.
Hypopigmentation is well described in 15q11.2-
q13 deletions (noted in Table II) due in large part to
heterozygous deletion of the P gene, but true
albinism can rarely occur when both P genes are
affected (e.g., one gene is missing due to the 15q11-
q13 deletion, while the other gene has a mutation)
[Fridman et al., 2003]. Of note, is a report of
retinochoroidal atrophy in several older AS indivi-
duals, suggesting that visual acuity may deteriorate
with aging [Rufa et al., 2003]. Better physical growth
to the extent that an overgrowth-like syndrome
more is known about these vision or growth issues,
no change was deemed needed in the consensus
Table II lists the clinical characteristics observed in
AS and conforms to a similar format used in the
original consensus project in that it lists estimated
percentages of clinical observations. The table is
intended to be applicable to the broad group of
individualswithAS, anditgenerally doesnotspecify
genotype–phenotype correlations to the respective
AS genetic mechanisms. The clinical diagnosis is not
usually suspected during the first year of life but
becomes a more frequent diagnostic consideration
between 1 and 4 years of age. AS can be diagnosed
The four features that are observed essentially in
100% of AS cases are unchanged compared to the
previous criteria study. We have however further
described or qualified them. The developmental
delay is still consistently in the functionally severe
range, but a number of reports, using psychometric
methods, now better define this severity. These
studies indicate that the ceiling for psychomotor
developmental achievement, on formal testing, is
around the 24–30 month range [Andersen et al.,
2001; Thompson and Bolton, 2003]. AS individuals
have relative strengths in visual skills and social
interactions that are based on non-verbal events. As
expected, expressive language abilities are more
impaired than receptive language abilities [Trillings-
gaard and Ostergaard, 2004].
Speech impairment continues to be a consistent
(100%) finding. In the original consensus statement,
the degree of severity was listed as involving ‘‘no or
minimal use of words.’’ It is now clear that some AS
individuals with a mosaic form of an imprinting
can speak in simple sentences [Nazlican et al., 2004].
The movement and balance disorder remains as
before although a caveat has been added that some
may have only mild gait or movement disturbances.
Behavioral uniqueness was the final category noted
to have 100% consistency. The only change recom-
mended in this category involves the removal of
‘‘short attention span’’ since one study demonstrated
that poor attention ability was less common in
children with AS than in non-AS controls who were
Regarding frequent clinical characteristics (more
than 80%) the three criteria are the same as noted in
1995: delayed or disproportionate head growth,
presence of seizures, and an abnormal EEG. Caveats
have been added indicating that microcephaly is
more prevalent with 15q11.2-q13 deletions [Moncla
et al., 1999; Lossie et al., 2001].
Epileptic seizures may persist into adulthood, and
the EEG abnormalities can precede clinical features
and/or may not be correlated with overt clinical
seizure events [Laan et al., 1996; Valente et al., 2003;
Laan and Vein, 2005]. There is no difference in EEG
TABLE III. 2005: Genetic Test Abnormalities in AS
1.Characteristic AS pattern of DNA methylation of the
SNURF-SNRPN exon 1/promoter. Detects cases due to
15q11.2-q13 deletion, UPD, and IDs (may have mosaic
methylation pattern in non-deletion IDs)
Abnormal FISH indicating a deletion of 15q11.2-q13 DNA
sequences withinthe commonAS deletion overlapregion.
Use of a pericentromeric FISH probe enhances the ability
to detect subtle translocation. Array-CGH can be used to
detect the deletion but confirmation by FISH is currently
required. Class I and II deletions can be distinguished by
array-CGH or FISH using appropriate clones
DNA polymorphism analysis within 15q11.2-q13 showing
Deletion in the Imprinting Center, demonstrated by real-time
PCR, single copy FISH, or other analysis methodsof the AS
Imprinting Center smallest region of overlap (SRO)
Pathogenic DNA sequence change in the UBE3A gene
AS, Angelman syndrome; UPD, uniparental disomy; FISH, Fluorescence in situ
hybridization; CGH, comparative genomic hybridization; sc, single copy; ID,
imprinting defect; PCR, polymerase chain reaction.
ANGELMAN SYNDROME 2005: UPDATED CONSENSUS
American Journal of Medical Genetics: DOI 10.1002/ajmg.a
findings in AS patients with or without epileptic
seizures, but the EEG findings are more pronounced
in AS patients with a deletion. Characteristic EEG
pattern appears in isolation or in different combina-
tions and consists of mainly three patterns: (1)
prolonged runs of rhythmic delta activity of 2–3 Hz
of large amplitude, most prominent in the frontal
regions and associated with superimposed epilepti-
in adults. (2) Persistent rhythmic 4–6 Hz activity of
large amplitude, seen under the age of 12 years, and
(3) spikes and sharp waves, mixed with 3–4 Hz
components of high amplitude, mainly posteriorly
et al., 1988; Laan and Vein, 2005]. The EEG can be
helpful to support the diagnosis of AS, especially in
patients without a genetic confirmation.
The list of associated findings has been expanded
but no feature has been deleted. Additions include
traits that are often seen in the older AS child or
young adult. They include abnormal food related
behaviors (e.g., eating non-food items, apparent
increased appetite, increased behavioral orientation
to food) [Barry et al., 2005], obesity [Clayton-Smith,
1993], scoliosis [Clayton-Smith and Laan, 2003], and
constipation. Attraction to or fascination with water
has been expanded to include fascination with
crinkly items such as certain papers and plastics.
The listing of ‘‘sleep disturbance’’ has been further
clarified to indicate abnormal sleep-wake cycles and
have also been described [Bruni et al., 2004; Miano
et al., 2004; Walz et al., 2005].
Individuals whose developmental history con-
forms to that described in Table I, and who have all
of the clinical findings of groups A and B in Table II,
should be considered for AS genetic testing. An
abnormal methylation test (see Table III) would
confirm the diagnosis, while detection of a deletion
by FISH could be compatible with a diagnosis of AS
or of Prader–Willi syndrome. Array-based compara-
tive whole genomic hybridization (array-CGH) can
be initially employed instead of FISH [Bejjani et al.,
should be confirmed by DNA methylation and by
FISH, and/or chromosome analysis to rule out
structural chromosome rearrangements. We have
made changes in Table III in order to add UBE3A
region should be used for the DNA methylation
testing. Table III also notes the occurrence of
methylation mosaicism for some IDs [Nazlican et al.,
2004] and capability of detecting ID deletions by
single copy FISH [Knoll and Rogan, 2003]. A positive
15% of individuals whose clinical presentation is
characteristic of AS, genetic laboratory studies of
deletion, UPD, ID, or UBE3A abnormality). If the
clinician is reasonably certain that the clinical
findings in Tables I and II are present, then the
diagnosis of AS could still be appropriate. This
situation may change as new testing and additional
testing is negative, but the clinical findings strongly
suggest the syndromic diagnosis. Indeed, the impor-
tance of a correct clinical diagnosis of AS is the main
reason for continued updating and dissemination of
the Consensus Criteria.
a somewhat uniform clinical picture of severe to
profound mental retardation, characteristic beha-
However, there are some clinical differences that
correlate with the genotype although there is great
variability within each group [Bottani et al., 1994;
Gillessen-Kaesbach et al., 1999; Moncla et al., 1999;
Fridman et al., 2000; Lossie et al., 2001; Varela et al.,
2004]. These correlations are broadly summarized
1. The deletion class is the most severely involved regarding
microcephaly, seizures, relative hypopigmentation, motor
difficulties (e.g., ataxia, muscular hypotonia, feeding difficul-
ties), and language impairment. Within the deletion group
BP1-BP3 breakpoints compared to those with BP2-BP3
deletions) may have more impairment in ability to speak
single words [Varela et al., 2004].
likely to have microcephaly) and have less movement and
ataxia abnormalities, and have a lower prevalence (but not
absence) of seizures.
and language ability. The most advanced speech abilities
occur in the ID group that is mosaic for the non-deletion
imprint defect (about 20% of the ID group) [Nazlican et al.,
2004]. These individuals may speak up to 50–60 words and
use simple sentences.
Other clinical disorders can mimic the features of
AS, especially during infancy. These include but are
not limited to Rett syndrome, 22q13.3 terminal
deletion, Mowat–Wilson syndrome, alpha-thalasse-
mia X-linked mental retardation (ATR-X) syndrome,
Lennox–Gastaut syndrome, static encephalopathy
with mental retardation, infantile autism, non-spe-
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American Journal of Medical Genetics: DOI 10.1002/ajmg.a