Molecular analyses in Indonesian individuals with intellectual disability and microcephaly
Abstract
Background Intellectual disability (ID) often coincides with anabnormal head circumference (HC). Since the HC is a reflection
of brain size, abnormalities in HC may be a sign of a brain anomaly.
Although microcephaly is often secondary to ID, hereditary
(autosomal recessive) forms of primary microcephaly (MCPH)
exist that result in ID.
Objective To investigate mutations in MCPH genes in patients
with ID and microcephaly.
Methods From a population of 527 Indonesian individuals with
ID, 48 patients with microcephaly (9.1 %) were selected. These
patients were previously found to be normal upon conventional
karyotyping, fragile X mental retardation 1 (FMRl) gene analysis,
subtelomeric deletion, and duplication multiplex ligationdependent
probe amplification (MLPA). Sanger sequencing for
abnormal spindle-like microcephaly-associated (ASPM) and WD
repeat domain 62 (WDR62) was performed in all 48 subjects, while
sequencing for microcephalin (MCPHl), cyclin-dependent kinase
5 (CDK5) regulatory subunit-associated protein 2 (CD5KRAP2) ,
centromere protein} (CENPJ), and SCUfALl interrupting locus
(STIL) was conducted in only the subjects with an orbitofrontal
cortex (OFC) below -4 SD.
Results In all genes investigated, 66 single nucleotide polymorphisms
(SNPs) and 15 unclassified variants which were predicted
as unlikely to be pathogenic (lN2), were identified. Possible
pathogenic variants (lN3) were identified in ASPM. However,
since none of the patients harboured compound heterozygous
likely pathogenic mutations, no molecular MCPH diagnosis could
be established. Interestingly, one of the patients harboured the
same variants as her unaffected monozygotic twin sister, indicating
that our cohort included a discordant twin.
Conclusions This study is the first to investigate for possible genetic
causes ofMCPH in the Indonesian population. The absence
of causative pathogenic mutations in the MCPH genes tested may originate from several factors. The identification of UV2
and UV3 variants as well as the absence of causative pathogenic
mutations calls for further investigations.
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Accepted 2016-08-19
Published 2013-04-30