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Sibs with tetrasomy 18p born to a mother with trisomy 18p
K Takeda1, T Okamura, T Hasegawa
1Department of Paediatrics, Yuri-Kumiai General Hospital, Honjo, Japan.
Insights
This study details a rare family with trisomy 18p and two daughters with tetrasomy 18p syndrome. The mother, phenotypically normal, carries an unusual de novo isochromosome 18p.
Area of Science:
- Genetics
- Human Genetics
- Chromosomal Abnormalities
Background:
- Trisomy 18p, a rare chromosomal condition, typically results from an extra copy of the short arm of chromosome 18.
- Isochromosomes, particularly i(18p), can lead to complex genetic imbalances and variable phenotypes.
- Understanding the inheritance patterns of such rearrangements is crucial for genetic counseling and reproductive planning.
Observation:
- A phenotypically normal mother with a de novo 47,XX,del(18)(pter----p11.21),+i(18p) karyotype is reported.
- Her older daughter exhibits features consistent with tetrasomy 18p syndrome, including microcephaly and developmental delay.
- The younger daughter was stillborn with severe congenital anomalies, including hydrocephalus and meningocele, also indicative of tetrasomy 18p.
Findings:
- Both daughters inherited a normal chromosome 18 and an isochromosome 18p from their mother, resulting in tetrasomy 18p.
- This represents a unique family where a mother with trisomy 18p due to an isochromosome has two affected daughters.
- The phenotypic spectrum of tetrasomy 18p is illustrated by the differing severity in the two sisters.
Implications:
- This case highlights the potential for significant genetic imbalance and severe phenotypes in offspring inheriting isochromosomes.
- It underscores the importance of detailed cytogenetic analysis in individuals with unexplained congenital anomalies.
- Further research into the mechanisms of isochromosome formation and segregation is warranted to improve understanding of these rare conditions.
Abstract:
We report a family with an 18p trisomic mother and two 18p tetrasomic daughters. The mother is phenotypically normal and healthy, but with an unusual type of trisomy 18p: 47,XX,del(18)(pter----p11.21),+i(18p) de novo. The older sister has microcephaly, mental retardation, an asymmetrical and peculiar face with low set ears, pinched up nose, high arched palate, small mouth, micrognathia, tapering fingers, asymmetrical length of legs, and an asthenic body. The younger sister was stillborn with extensive defects of the skull, congenital hydrocephalus, severe facial anomalies, and lumbosacral meningocele. Both daughters have inherited one normal chromosome 18 and an isochromosome 18p from their mother, and one normal chromosome 18 from their father. Although one quite similar family has been reported, to the best of our knowledge there have been no reports of families in which two daughters with tetrasomy 18p syndrome have been born to a mother with trisomy 18p with isochromosomes.