Prenatal Diagnosis of Poretti-Boltshauser Syndrome - a Case Report of a Molar Tooth Sign Mimic.

We report the prenatal diagnosis of Poretti-Boltshauser Syndrome (PBS) in a 36-year-old primigravida woman. At 22 weeks and 6 days of gestation, fetal ultrasound revealed a normally shaped but hyperechogenic cerebellum with all supratentorial structures appearing normal. Differential diagnosis included cavernous hemangioma, capillary telangiectasia, and cerebellar hemorrhage. Subsequent fetal cerebral MRI showed diffuse bilateral cerebellar modifications, reduced cranio-caudal diameter of the vermis, and pathological elongation and thickening of the superior cerebellar peduncles indicative of the molar tooth sign. Amniocentesis and whole exome sequencing identified two heterozygous truncating variants in the LAMA1 gene: c.3099G > A (p.Trp1033Ter) and c.3699T > A (p.Tyr1233Ter), confirming PBS.) Following the diagnosis, the pregnancy was terminated at 23 weeks and 5 days. Post-mortem examination supported the MRI findings consistent with PBS. This case highlights the importance of integrating ultrasound, MRI, and genetic analysis for accurate prenatal diagnosis and emphasizes the molecular diversity associated with PBS, including the presence of molar tooth sign mimics and a novel c.3699T > A variant.