Clinical and Cytogenomic Characterization of Three Patients With Distal 1q43q44 Deletion: Twin Sisters With a de novo Deletion and a Patient With der(1)t(1;21)(q43;q22.3)mat.

BACKGROUND

Deletions involving the 1q43q44 region are among the most recurrent terminal chromosomal imbalances and are associated with a recognizable neurodevelopmental phenotype. These deletions may occur as isolated events or in the context of more complex rearrangements.

CASE PRESENTATION: We describe presumed monozygotic twin sisters (patients 1 and 2) with a de novo 1q43q44 deletion and an unrelated patient (patient 3) carrying a similar deletion combined with a 21q22.3 duplication derived from a t(1;21)(q43;q22.3)mat. All three patients exhibited features consistent with the distal 1q43q44 deletion syndrome, including microcephaly, corpus callosum abnormalities, developmental delay, intellectual disability, language impairment, hypotonia, micro-/retrognathia, and congenital heart defects.

RESULTS

Cytogenetics and FISH analyses confirmed distal 1q deletions in all patients. Chromosomal microarray analysis identified a ~9.5 Mb deletion in patient 1 (her twin was not tested) and a ~12.1 Mb deletion in patient 3. Despite differences in deletion size and genomic context, both rearrangements disrupted a largely overlapping interval containing 171 genes, including the dosage-sensitive neurodevelopmental genes AKT3, HNRNPU, and ZBTB18 as well as other monoallelic expressed genes (GREM2 and NLRP3) and, in patient 3 only, RYR2. Functional enrichment analyses highlighted pathways related to neurodevelopment, epilepsy, and cardiac function. Although the twins showed similar congenital manifestations, patient 1 later developed seizures whose origin could not be assessed.

CONCLUSION

These findings further support the role of haploinsufficient genes within the distal 1q43q44 region, particularly AKT3, HNRNPU, and ZBTB18, to the core neurodevelopmental phenotype and highlight the value of high-resolution genomic analysis for patient characterization.