Numerical Chromosomal Abnormalities

Frequency ~1/5000 female live births

Newborns are fully viable, but 99% of 45,X spontaniously aborted

• ~50% of cases involve 45,X:
• • The monosomy is usually due to a paternal meiotic error (X present is from the mother)
• • Remaining cases also lack chromosomal material from one X

Frequency: 1/800 live births (but majority spontaneously abort)

• ~95% of cases involve Trisomy 21 (47,XY,+21 or 47,XX,+21)
• • Usually due to non-disjunction in maternal meiosis
• • Associated with AMA

• Remaining cases are not related to
• AMA and may have higher
• recurrence rates for future pregnancies: • Rob translocation involving 21q [e.g., der(14;21)]
• • i(21q)
• • Trisomy for only part of 21q
• • Must karyotype affected child to estimate recurrence risk

Incidence: 1:20,000- 1:25,000

• Phenotype:
• Congenital heart defects,
• holoprosencephaly, micropthalmia,
• cleft lip/plate, polydactyly, urogenital
• defects, clenched fists, rocker-bottom
• feet, severe MR, growth retardation
• (50% survive < 1 mo)

About 1/5 cases involve a translocation of chromosome 13

Incidence: 1:6000- 1:8000

• Phenotype:
• Congenital heart defects, failure to
• thrive, malformed & low-set ears,
• prominent occiput, receding jaw, short sternum, characteristic clenched fist
• (2nd finger overlaps 3rd, 5th overlaps 4th finger), rockerbottom
• feet, MR (few survive to 1 yr)

About 1/5 of cases involve a translocation of chromosome 18

• Complete moles are disorders of imprinting!
• Phenotype results because gene expression from the maternal and
• paternal genomes is not equivalent!
• (46,XX 90%)

No fetal tissue present

• Endoreduplication of haploid sperm after fertilizing an ovum lacking
• a nucleus (only paternal
• genome present)

Risk of progression to choriocarcinoma

Triploidy: 69 XXX or 69,XXY

Fetal tissue present

• Fertilization of a haploid ovum and duplication of the paternal haploid
• chromosomes or from dispermy

No risk of progression to choriocarcinoma