Practice question

Patau syndrome results extra chromosome 13, karyotype 47,XY+13 or XX+13 free trisomy, incidence about 1 in 15000 live births with much higher prenatal lethality. Phenotypic spectrum includes severe central nervous system malformations holoprosencephaly midline defects, microphthalmia, cleft lip palate bilateral, polydactyly postaxial extra digits, scalp defects cutis aplasia, cardiac anomalies septal defects, high neonatal lethality within days weeks median 7-10 days. Chromosome 13 larger than 18 and 21, dosage disruption profound affecting many patterning genes. Mosaic cases with normal cell line proportion may show attenuated features surviving longer months.