Down syndrome in two of three triplets

Area of Science:

• Human Genetics
• Reproductive Biology
• Perinatology

Background:

• Down syndrome (trisomy 21) is a genetic disorder.
• Twinning is a complex reproductive event with reported associations with chromosomal abnormalities.
• The incidence of Down syndrome in twins may be higher than in singletons.

Observation:

• A set of triplets was born to a 22-year-old woman with a family history of multiple twin births.
• Two of the triplets were diagnosed with Down syndrome and were monozygotic.
• The third triplet was non-identical, and neither parent exhibited chromosomal abnormalities.

Findings:

• This is the first documented instance of trisomy 21 occurring in two members of a triplet set.
• Zygosity was determined through red blood cell antigen and HLA typing.
• The affected twins were monozygotic, while the third sibling was dizygotic.

Implications:

• The case supports the hypothesis of a heritable predisposition to both twinning and chromosomal abnormalities.
• Further research into familial predispositions for twinning and genetic disorders is warranted.
• This case highlights the complex interplay between genetics, twinning, and chromosomal abnormalities.