Table 2.

Selected Recurrence-Risk Estimates Calculated from Our Analyses

Parent	Age	Mosaic in Blood	Recurrence-Risk Estimates
			Risk Haplotype				Unknown Haplotype
			One Affected and Zero Unaffected	One Affected and One Unaffected	Two Affected and Zero Unaffected	Three Affected and Zero Unaffected	One Affected and One Unaffected
Mother	any	unknown	2.60%	2.48%	4.95%	7.07%	2.54%
Father	20	unknown	0.235%	0.234%	0.468%	0.699%	0.235%
Father	25	unknown	0.142%	0.142%	0.28%	0.42%	0.142%
Father	30	unknown	0.102%	0.102%	0.203%	0.305%	0.102%
Father	35	unknown	0.080%	0.079%	0.159%	0.238%	0.080%
Father	40	unknown	0.065%	0.065%	0.130%	0.195%	0.065%
Father	50	unknown	0.048%	0.048%	0.096%	0.143%	0.048%
Unknown	30	unknown	0.197%	–	–	–	–
Unknown	50	unknown	0.094%	–	–	–	–
Mother	any	yes	5.21%	4.72%	9.40%	12.9%	4.96%
Father	any	yes	5.21%	4.72%	9.40%	12.9%	4.96%

Information gained about recurrence risk from observation of unaffected offspring depends on the chromosome haplotype inherited from the parent who transmitted the mutant allele to the affected offspring. Inheriting the chromosome on which the mutation occurred (the risk haplotype) but with a wild-type allele provides much more information than inheriting the homologous chromosome’s haplotype. Absence of evidence of somatic mosaicism is treated as unknown because only a subset of tissue can be tested. Updating recurrence risk on the basis of additional offspring for an unknown transmitting parent is not considered in this manuscript. We caution against using this model-based table directly in clinical practice.