A missense variant, p.(Ile269Asn), in MC4R as a secondary finding in a child with BCL11A-related intellectual disability

BCL11A intellectual developmental disorder: defining the clinical spectrum and genotype-phenotype correlations

An increasing number of individuals with intellectual developmental disorder (IDD) and heterozygous variants in BCL11A are identified, yet our knowledge of manifestations and mutational spectrum is lacking. To address this, we performed detailed analysis of 42 individuals with BCL11A-related IDD (BCL11A-IDD, a.k.a. Dias-Logan syndrome) ascertained through an international collaborative network, and reviewed 35 additional previously reported patients. Analysis of 77 affected individuals identified 60 unique disease-causing variants (30 frameshift, 7 missense, 6 splice-site, 17 stop-gain) and 8 unique BCL11A microdeletions. We define the most prevalent features of BCL11A-IDD: IDD, postnatal-onset microcephaly, hypotonia, behavioral abnormalities, autism spectrum disorder, and persistence of fetal hemoglobin (HbF), and identify autonomic dysregulation as new feature. BCL11A-IDD is distinguished from 2p16 microdeletion syndrome, which has a higher incidence of congenital anomalies. Our results underscore BCL11A as an important transcription factor in human hindbrain development, identifying a previously underrecognized phenotype of a small brainstem with a reduced pons/medulla ratio. Genotype-phenotype correlation revealed an isoform-dependent trend in severity of truncating variants: those affecting all isoforms are associated with higher frequency of hypotonia, and those affecting the long (BCL11A-L) and extra-long (-XL) isoforms, sparing the short (-S), are associated with higher frequency of postnatal microcephaly. With the largest international cohort to date, this study highlights persistence of fetal hemoglobin as a consistent biomarker and hindbrain abnormalities as a common feature. It contributes significantly to our understanding of BCL11A-IDD through an extensive unbiased multi-center assessment, providing valuable insights for diagnosis, management and counselling, and into BCL11A's role in brain development.

Dias-Logan syndrome with a de novo p.Leu360Profs*212 heterozygous pathogenic variant of BCL11A in a Chinese patient: A case report

Dias-Logan syndrome, also known as intellectual developmental disorder with persistence of fetal hemoglobin (HbF), or BCL11A-related intellectual developmental disorder, is an extremely rare neurogenetic disorder characterized by intellectual disability (ID), delayed psychomotor development, variable dysmorphic features, and asymptomatic persistence of fetal hemoglobin. The prevalence and incidence of this condition are currently unknown. We report an 8-year-old Han Chinese male patient with Dias-Logan syndrome who carries a de novo heterozygous pathogenic variant, c.1078dupC (p.Leu360Profs*212), in the BCL11A gene, leading to ID and γ-globin suppression, identified through trio-based whole exome sequencing (trio-WES). All his blood parameters were normal except for an elevated HbF level, which was 19.9% of total hemoglobin. Given the negative family history for ID, epilepsy, and alcohol consumption, de novo inheritance was presumed. Consequently, trio-WES analysis (parents and child) was conducted as it can identify potential new causal variants in the offspring. So far, a comprehensive understanding of the phenotypic spectrum of Dias-Logan syndrome and the impact of genotypic variation on disease severity is still lacking. Therefore, our case report enriches the existing literature on the clinical spectrum and genotype-phenotype correlations of BCL11A-related syndrome and provides some helpful information for diagnosis, management, and genetic counseling.