الفهرس 
Intellectual Disability
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Abstract
Intellectual disability (ID) is characterized by
significant limitations in intellectual functioning and
adaptive behavior and is often associated with
developmental delay and multiple congenital anomalies. It
has a major effect on the life of the affected person his
family and the society and it is a frequently occurring
disorder.
The study of the intellectual disability is complicated
because of the high clinical and genetic heterogeneity.
Intellectual disability can be caused by genetic defects as
well as environmental causes affecting the development
and function of the nervous system. Although Intellectual
disability can be caused by environmental insults but a
large proportion is caused by genetic abnormalities. Still,
around 60% of cases of Intellectual disability do not have a
known etiology.
Systematic assessment of a child with intellectual
disability has many steps starting with detailed history, full
physical examination, and screening laboratory testing.
Karyotype considered the traditional diagnostic test for
genetic evaluation in patients with idiopathic non- syndromic intellectual disability. Other tests include
screening tests, metabolic tests, TORCH screens, and
neuroimaging, all of which have limited diagnostic value.
Chromosomal analysis using the classical cytogenetic
studies is considered the standard method for investigating
syndromes suspected to have a chromosomal etiology but it
cannot detect chromosomal imbalances smaller than 5-10
Mb. So, many subtelomeric copy number variance
especially those close to the telomeres cannot be detected
by conventional karyotype.
Subtelomeric regions are gene-rich parts of the
chromosome. Microdeletions and subtelomeric
rearrangements that disrupt genes in the telomeric region
can cause intellectual disability. The identification of
subtelomeric copy number variance as the genetic cause of
intellectual disability is of high value because it allows
proper medical care, genetic assistance and prognosis. The
majority of cases with subtelomeric copy number variance
had no characteristic phenotype, so a general subtelomeric
screen is required to reach a diagnosis.
Molecular studies focusing on subtelomeric copy
number variance in patients with idiopathic intllecual
disability have been performed mainly by FISH using subtelomere specific probes. Commercial subtelomeric
FISH is expensive, time consuming and laborious so
different approaches had been tried. from these methods
MLPA technique, it is a very promising technique. It
appears to represent an improvement compared to the
laborious and costly FISH.
MLPA is a sensitive and reliable technique for the
detection of subtelomeric copy number variant. It is
molecular genetic technique that identifies subtelomeric
copy number variance, such as duplications or deletions.
MLPA consists of comparative quantification of
specifically bound probes that are amplified by PCR with
universal primers. MLPA is an easy-to-perform reaction
requiring only 20 ng of human DNA.
We recommend to start with cytogenetics study in
patient with intellectual disability if no abnormalities
detected proceed to MLPA which is a targete test used for
screening of large number of intellectual disability patients
in short time with low cost, positive cases with MLPA
should be confirmed by FISH. If no abnormality detected
by MLPA proceed to array CGH.
The aim of our study was to determine the prevalence,
and characterization of copy number variance of subtelomeric regions through the multiplex ligation
dependent probe amplification (MLPA) method in pediatric
patients with idiopathic intellectual disability.
This study was conducted on 30 selected patients who
had intellectual disability attending Genetic Clinic,
Pediatric Hospital, Ain Shams University and Outpatient
clinics of the Clinical Genetic Department, National
Research Centre.
The study group included 30 patients with idiopathic
intellectual disability and normal karyotype as major
criteria. Minor criteria included dysmorphic features,
nonfacial dysmorphism or congenital anomalies abnormal
growth, behavioral disorder, family history of intellectual
disability and/or family history of miscarriages or perinatal
death as the patients group. Patients were subjected to full
medical history, pedigree analysis and physical
examination.
3 patients with intellectual disability and chromosomal
aberrations as detected by karyotype were included as
positive controls with provisional diagnosis by karyotype
for the technique and 6 normal persons as a negative
control group All patients were subjected to the following:
a) Clinical Evaluation:
1. Medical history: included age, sex, and history of the
present illness.
2. Pedigree Analysis: this was performed for the
patients taking in consideration consanguinity,
similarly affected siblings and other affected family
members.
3. Physical examination:
General physical examination was done for all
patients.
Anthropometric measurements at the time of
clinical assessment as regard to weight,
length/height and head circumference were
assessed.
b) Laboratory method:
1. DNA extraction: 8ml of venous blood on PAXgene
tube for DNA extraction by PAXgene DNA
purification kit and measurement of quality and
concentration of DNA (PreAnalytix, Hiden,
Germany).2. Multiplex Ligation-dependent Probe Amplification
(MLPA) (MRC-Holland 2002): The MLPA assay
was performed using the SALSA MLPA probemix
P070 Subtelomeres Mix 2B. MLPA analysis was
carried out as recommended by the manufacturer.
3. Fluorescence in situ hybridization (FISH) to confirm
positive results according to (Pinkel et al., 1986).
The results showed that:
All 30 selected patients subjected to subtelomeric
screening by multiplex ligation dependent probe
amplification using P070 kit revealed no Subtlomeric copy
number variance in any of the patients included.
On the other hand; the 3 positive control patients
showed abnormalties by MLPA confirmed by FISH
analysis. Positive control patient number one showed by
karyotype abnormality in q arm of chromosome 1. When
included as positive case in MLPA analysis both 1q
subtelomere deletion and 4q subtelomere duplications were
detected. FISH was done using subtelomere 4q and 1q
pobes and revealed deletion of 1q subtelomere and
duplications 4q subtelomere as detected by MLPA. Positive
control patient number two showed by karyotype
abnormality in q arm of chromosome 22 when included as positive case in MLPA analysis 9p subtelomere duplication
was revealed. FISH was done using 9p subtelomere probe
and showed duplication in 9p. Positive control patient
number three showed by karyotype abnormality in q arm of
chromosome 14. When included as positive case in MLPA
analysis 9p subtelomere duplication was revealed. FISH
was done using total subtelomere 9p probe and showed
duplication in 9p subtelomere. The length of deletion and
duplication needs further investigation including
microarray for detection of the exact length or whether it is
limited to subtelomere or other areas are included