Inherited Cryptic Translocation t(12;17)(q24.3;p13.3) Causing Recurrence of Miller-Dieker Syndrome

The Miller-Dieker syndrome (MDS) is a severe neurological disorder characterized by lissencephaly, facial dysmorphies, global developmental delay and severe seizures. A deletion at 17p13.3, including the lissencephaly gene (LIS1), is usually present as part of a contiguous gene syndrome. Around 20% of case LSI1 gene is resulting from inherited balanced translocation. We present the case of a family with cryptic t(12;17) translocation identified by FISH in two generations. The proband had clinical features of MDS. The parents reported a paternal aunt deceased as a young infant due to “uncontrolled seizures and severe developmental delay. The GTG analysis of proband suggested deletion at 17p13.3 that was confirmed by FISH. The parental investigation by FISH revealed a paternal translocation involving regions 12qter and 17p13.3. This familial chromosomal rearrangement associated to MDS has modified the genetic counseling of the couple. From a very low risk of recurrence on the cases associated to a de novo del17p13.3, to a much higher risk, since it was associated to a familial translocation. This risk of recurrence, considering meiotic segregation of balanced translocation involving the 17p13.3 region is relatively high (12%) which alone would justify prenatal diagnosis. Classical and molecular cytogenetic investigations in the fetal sample were normal reassuring the couple as to a normal baby with neither 17p13.3 deletion nor carrier of the paternal translocation. This rare case identified by FISH demonstrate the need of providing molecular cytogenetic analysis for other family members; since, criptical balanced rearrangements may segregate undetected. This case evidences the importance of molecular study of parents of children with microdeletions, which could considerably improve the certainties regarding genetic counseling