Trisomy 13 with unusual histological features typically described in Beckwith-Wiedemann Spectrum.

Trisomy 13, known as Patau syndrome, is a common aneuploidy with a well-known clinical phenotype. This case report describes a trisomy 13 patient with unusual autopsy findings, including features resembling the Beckwith-Wiedemann Spectrum. Due to abnormalities of gestational ultrasounds, a prenatal karyotype of amniotic fluid cells was performed, which resulted in 47, XY+13. Autopsy microscopy studies identified leptomeningeal glioneuronal heterotopia, which was not described as belonging to Patau syndrome. Other atypical findings were diffuse hyperplasia of pancreatic islets of Langerhans and adrenals enlargement with marked adrenocortical cytomegaly, characteristically seen in the Beckwith-Wiedemann Spectrum. Molecular genetic tests were not performed for the Beckwith-Wiedemann Spectrum. Still, due to the rarity of both disorders, this report may support the evidence that trisomy 13 can affect tissue organization and lead to unusual histopathologic features resembling classic overgrowth disorders.

Imagawa-Matsumoto syndrome: SUZ12-related overgrowth disorder.

The SUZ12 gene encodes a subunit of polycomb repressive complex 2 (PRC2) that is essential for development by silencing the expression of multiple genes. Germline heterozygous variants in SUZ12 have been found in Imagawa-Matsumoto syndrome (IMMAS) characterized by overgrowth and multiple dysmorphic features. Similarly, both EZH2 and EED also encode a subunit of PRC2 each and their pathogenic variants cause Weaver syndrome and Cohen-Gibson syndrome, respectively. Clinical manifestations of these syndromes significantly overlap, although their different prevalence rates have recently been noted: generalized overgrowth, intellectual disability, scoliosis, and excessive loose skin appear to be less prevalent in IMMAS than in the other two syndromes. We could not determine any apparent genotype-phenotype correlation in IMMAS. The phenotype of neurofibromatosis type 1 arising from NF1 deletion was also shown to be modified by the deletion of SUZ12, 560 kb away. This review deepens our understanding of the clinical and genetic characteristics of IMMAS together with other overgrowth syndromes related to PRC2. We also report on a novel IMMAS patient carrying a splicing variant (c.1023+1G>C) in SUZ12. This patient had a milder phenotype than other previously reported IMMAS cases, with no macrocephaly or overgrowth phenotypes, highlighting the clinical variation in IMMAS.