De novo isochromosome 18p in a female dysmorphic child.
Isochromosome 18p results in tetrasomy 18p. Most of the i(18p) cases reported so far in the literature are sporadic due to de novo formation, while familial and mosaic cases are infrequent. It is a rare chromosomal abnormality, occurring once in every 140,000 livebirths, affecting males and females equally. In the present investigation, we report a de novo i(18p) in a female dysmorphic child. The small metacentric marker chromosome was confirmed as i(18p) in the proband by cytogenetic and FISH analysis [47,XX+i(18p)]. Cytogenetic investigations in the family members revealed normal chromosome numbers, indicating the case as a de novo event of i(18p) formation. It could be due to the somewhat advanced maternal age (32 years) and/or expression of recessive genes in the proband, who is the progeny of consanguineous marriage, which could have led to misdivision and nondisjunction of chromosome 18 in meiosis I, followed by failure in the chromatid separation of 18p in meiosis II and by inverted duplication.
Ramegowda
Smitha
S
Human Genetics Laboratory, Department of Studies in Zoology, University of Mysore, Manasagangothri, and Department of Pediatrics, Cheluvamba Hospital, Mysore 570 006, India.
Gawde
Harshavardhan M
HM
Hyderi
Abbas
A
Savitha
Mysore R
MR
Patel
Zareen M
ZM
Krishnamurthy
Balasundaram
B
Ramachandra
Nallur B
NB
D000015:Abnormalities, Multiple / Q000235:genetics*; D002648:Child; D002874:Chromosome Mapping; D002887:Chromosomes, Human, Pair 18; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D018404:Isochromosomes