# De Novo Balanced Translocation t (7;16) (p22.1; p11.2) Associated with Autistic Disorder

Authors: Nadia Bayou; Ridha M'rad; Ahlem Belhaj; Hussein Daoud; Lamia Ben Jemaa; Ramzi Zemni; Sylvain Briault; M. Bechir Helayem; Habiba Chaabouni
Journal: Journal of Biomedicine and Biotechnology
 (2008-02-18)

---

## Abstract

The high incidence of de novo chromosomal aberrations in a population of persons with autism suggests a causal relationship between certain chromosomal aberrations and the occurrence of isolated idiopathic autism. We report on the clinical and cytogenetic findings in a male patient with autism, no physical abnormalities and a de novo balanced (7;16)(p22.1;p16.2) translocation. G-banded chromosomes and fluorescent in situ hybridization (FISH) were used to examine the patient's karyotype as well as his parents'. FISH with specific RP11-BAC clones mapping near 7p22.1 and 16p11.2 was used to refine the location of the breakpoints. This is, in the best of our knowledge, the first report of an individual with autism and this specific chromosomal aberration.


---

## Body

## 1. Introduction

Autism
is a relatively common and heterogeneous neuropsychiatric disorder characterised
by reduced social and interindividual contacts and interactions. Autism usually
starts in early childhood. Complete absence of eye contact and speech can be
observed in severe forms of autism [1].
Its incidence is estimated at about
1/1000 to 1/2000 with a biased male-to-female ratio of three or four to one
(3-4 : 1) [2]. Studies of familial cases have demonstrated that
genetic factors are involved in the aetiology of autism [3]. A
number of balanced and unbalanced chromosomal aberrations have been found to be
associated with autism [4–6].In
this study, we describe a reciprocal translocation t(7;16)(p22.1;p11.2) that
occurred de novo in a 10-year-old boy with autism and psychomotor retardation
and only minor additional anomalies or dysmorphic features. Neither chromosomal
breakpoint has been mentioned in previous reports of cytogenetic aberrations
seen in patients with autistic behaviour.


## 2. Case Report

The
10-year-old patient is the younger of two children born at term from nonconsanguineous
healthy parents. The father and the mother were, respectively, 34 and 30 years old
when the child was born. Pregnancy was uneventful. Delivery was by caesarean
section secondary to a narrow basin. Birth weight was 3350 kg, and no recognized
malformations were noted. His older sister is healthy and developmentally
normal.Patient’s
psychomotor delays were noticed in the first months of life by his parents; they also reported frequent crying and sleep disturbances. He was unable to
maintain eye contact and presented many motor stereotypes and ritualistic
behaviours such as cutting papers into small pieces and aligning objects. Clinical
assessment showed a boy with no dysmorphic signs (see Figure1).Figure 1
The phenotype of
the patient.At the
age of 4 years and 11 months, the patient was examined by an experienced child
psychiatrist who found impairments in social interaction and communication
according to the Diagnostic and
Statistical Manual-revision 4 (DSM-IV) and the Autism Diagnostic
Interview (ADI-R), French version 1993, criteria and made the clinical
diagnosis of autism.Routine
hearing tests and amino acid chromatography were normal. Brain CT
scan revealed a cerebellar megacysterna in the posterior fossa and a temporal
arachnoidal cyst. The electroencephalogram was normal. Southern blot analysis revealed
the absence of FRAXA mutation.


## 3. Materials and Methods

Chromosomal
abnormalities have been identified by using traditional cytogenetics and
fluorescent in situ hybridization (FISH).Chromosomes
were prepared from phytohemagglutinin
(PHA) stimulated peripheral blood lymphocytes of the proband and his
parents following standard procedures. The healthy sister was not available for
analysis. All chromosome preparations were G-banded and then analysed.For FISH
analysis, metaphase spreads obtained from an Epstein
Barr virus (EBV) immortalised cell line from the
patient were hybridised with bacterial artificial chromosome clones (BACs). The
RPCI-11 BAC clones covering genomic regions on both chromosomes were selected
according to the UCSC Genome browser (http://www.genome.ucsc.edu/) and Ensembl genome
database (http://www.ensembl.org/Homo_sapiens/). They were provided by BACPAC resource
centre (BPRC) (http://bacpac.chori.org) and professor Mariano Rocchi (University of Bari, Italy). Thesequence limits of the BACs were defined according to DECIPHER
database (https://enigma.sanger.ac.uk/perl/PostGenomics/decipher).BAC
clones were biotinylated with biotin-11-dUTP (Sigma) by nick translation using
the Bio Nick labelling system (Invitrogen Life Technologies). For the double
colour FISH experiment, one probe was labelled with biotin-11-dUTP and the
second probe, a commercially one, with Rhodamine (QBiogen).


## 4. Results

Routine
and high-resolution chromosome studies revealed a de novo translocation carried
by the proband. The G-band pattern suggested a balanced translocation involving
7p22 and 16p11.2
and established the karyotype as 46,XY,t(7;16)(p22; p11) (see Figure2). The
parent karyotypes were normal. To identify the translocation breakpoints, we
used 16 bacterial artificial chromosome clones (BACS) from 7p22 and 16p11 in
fluorescence in situ hybridization (FISH) analysis (see Table 1).Table 1
FISH results using BAC clones on 7p and 16p regions.
RP11 clone IDMap positionStart*End*FISH signal on normal chromosome 7FISH signal on Derivative 7FISH signal on normal chromosome 16FISH signal on Derivative 16368N2116p11.22940869929609853−++−261H516p11.23112073931307726−++−120K1816p11.23116367731329206−++−264M1416p11.23328242333452774−+++341P616p11.23426301634452072−+++104C416p11.23336222233555929−−++488I2016p11.23435984134490213−−++449P157p22.38851031079306+−−+42B77p22.241264624281105+−−+33P217p22.145591414711177+−−+32P37p22.147111784751000+−−+160E177p22.147510014911018+−−+805D57p22.149110194933256+−−+730B227p22.149332575107654++−+147A227p22.151838225357984++−−1275H247p22.154271685510299++−−425P57p22.162339876446613++−−+: presence of the signal hybridization.−: absence of the signal hybridization.*: nucleotide position according to DECIPHER (https://enigma.sanger.ac.uk/perl/PostGenomics/decipher).Partial GTG-banding karyotype of the patient. The patient derivative chromosomes 7 and 16 are shown. By comparing both respective ideogrammed
chromosomes, the breakpoints were located in 7p22 and 16p11.2.
(a)(b)As shown
in Figure3(a), the RP11-730B22 BAC hybridized to both derivative 7 and the
derivative 16 and the normal chromosome 7, but not to the normal chromosome 16,
indicating that this clone spans the translocation breakpoint on chromosome 7.FISH analysis of the translocation
breakpoints: (a) FISH analysis with the BAC RP11-730B22 (green) located in
7p22.1 and a centromeric probe of chromosome 16 (red), shows that this BAC is
spanning the breakpoint on chromosome 7. (b) FISH analysis with BACs RP11-264M14 (green) showed that it spans the translocation
breakpoint located on 16p11.2. It was hybridised with a chromosome 7
centromeric probe (red). (Chr.: chromosome, Der.: derivative).
(a)(b)Although
we did not identify the actual sequence of the breakpoint on 7p22.1, we located
it by BAC-FISH mapping between nucleotides 4933257 and 5107654.According
to Ensembl genome database (May 2006 version), there are 3 coding sequences corresponding
to NP_976327.1, RBAK (RB-associated KRAB zinc finger) and RNF216L or Q6NUR6
(E3 UBIQUITIN LIGASE TRIAD3 EC6.3.2.) genes.Seven but
four BAC clones located on 16p11.2 gave two distinct hybridization signals on
the normal 16p and the derivative 16 (see Table1). The overlapping BAC,
RP11-264M14, hybridized to both derivative 16 and derivative 7 chromosomes and to
the normal chromosome 16, but not to the normal chromosome 7 (see Figure 3(b)).
The clone RP11-264M14, on 16p11.2, was found to be devoid of known genes.


## 5. Discussion

Genetic studies have yielded suggestive linkage and association to several
different chromosomal regions, but up to now, the large number of association
studies using a candidate gene approach has had limited success [7–10]. As an
alternative approach, the characterisation of different types of chromosomal abnormalities
could result in the identification of candidate genes for autism [11, 12]. Chromosomal abnormalities
detected by cytogenetics or molecular cytogenetics are of major aid to locate
relevant genes. About 3–5% of autistic patients have a chromosome abnormality
visible with cytogenetic methods [13]. Almost all chromosomes have been
involved including translocations and inversions resulting in disruption of
genes at the breakpoints [14, 15].Balanced
chromosome rearrangements are observed at a significantly increased rate.
Gillberg and Wahlström [16], in an epidemiological study done on 66 individuals with autism located in Sweden, found that less than 5% of
the group had major chromosomal abnormalities. The same rate was found by
Castermans et al. [17] when they karyotyped 525 individuals
with idiopathic autism. This rate is much higher than would be expected from a
general population (1/2000 for a reciprocal translocation and 1/10000 for an
inversion) [18]. This suggests that certain chromosome aberrations
like translocations, deletions, or inversions may involve genes acting as susceptible
factors for autism.In this
article, we describe a 10-year-old child carrying a de novo balanced (7;16)(p22.1;p16.2) translocation associated with an autistic disorder, psychomotor delays,
and no dysmorphic features.This case
represents both an unusual and useful
opportunity to examine and compare the cytogenetic and the common physical
features with the previously reported cases of autism and these specific
regions. In Table2, an overview is given of all patients with chromosomal
anomalies involving the 7p22.1 and 16p11.2 regions that have been described in
the literature. In the best of our knowledge, it is the first time the autism
phenotype has been associated with a translocation in these specific
chromosomal regions.Table 2
Autism related breakpoints on 7p22p and 16p11.2.
ChromosomeKaryotypePhenotypeReferenceChr1646, XX, dir dup(16)(p11.2p12.1)autism, mild mental retardationFinelli et al. [20] Engelen et al. [21]Chr1646, XY, dir dup(16)(p11.2p12) de novoautistic behaviour, psychomotor retardationCarrasco Juan et al. [22]Chr1646, XY, inv(2)(p11.2q13), 16qh-autismVorsanova et al. [23]Chr7del  (7)(p22.2p22.2)autismYu et al. [24]Chromosome
16p has been identified by a number of genome screens for autism and is likely
to contain an autism-susceptibility variant. The 7p locus has been less
consistently reported than the chromosome 16p one. Both regions remain an
important area for future research [19].Regarding
the locus on 16p11.2, only duplications and one inversion have been reported [20–23]. Looking at the overall clinical phenotype of our patient and the
literature described ones, the only shared features seem to be autistic
behaviour. The observed phenotypic variety may be caused by the dissimilarity
in the nature of the chromosomal abnormalities and by the size and the content
of the interval.Large-deletion
alleles on chromosome 7p22 were found in kindreds with autism but not in healthy
control subjects [24]. In these regions, genes are likely to
contribute to autism in the individuals with the cytogenetic abnormality but
appear to lack a significant effect at the population level. More than 100 genes have been mapped in the deleted interval
(http://genome.ucsc.edu/), and so
it is only possible to speculate about the potential role of specific genes in
autism.According
to Ensembl genome databases, there are few genes listed in the breakpoint region
on 7p22.1 : NP_976327.1, which is a
hypothetical gene expressed in the cerebellum, RBAK gene may contribute to
transcriptional activation and cell cycle arrest and RNF216L or Q6NUR6 gene which may be an E3 ubiquitin ligase. On the basis of
their functions and expression patterns, these genes can be considered as
candidate genes for autism.Interestingly,
the disruption of one of these genes by the translocation may cause a decreased
dosage responsible for specific tissue and developmental effects leading to
autistic traits. This is in agreement with the deletions on 7p22 reported on
autistic patients by Yu et al. [24].The characterisation
of the translocation breakpoints will let as to narrow the interval and to
identify candidate genes causative of the observed phenotype in our patient.In conclusion, the case report presented here (1) places further
emphasis on the importance of molecular cytogenetics in the study of de novo
apparently balanced translocations with abnormal phenotype and (2) confirms the
possibility that genes with an important contribution to the pathogenesis of
autism are located in regions of the genome for which cytogenetic abnormalities
have not been reported so far.



---

*Source: 231904-2008-04-23.xml*