Heterozygous pathogenic variants involving CBFB cause a new skeletal disorder resembling cleidocranial dysplasia

BACKGROUND

Cleidocranial dysplasia (CCD) is a rare skeletal dysplasia with significant clinical variability. Patients with CCD typically present with delayed closure of fontanels and cranial sutures, dental anomalies, clavicular hypoplasia or aplasia and short stature. Runt-related transcription factor 2 (RUNX2) is currently the only known disease-causing gene for CCD, but several studies have suggested locus heterogeneity.

METHODS

The cohort consists of eight subjects from five unrelated families partially identified through GeneMatcher. Exome or genome sequencing was applied and in two subjects the effect of the variant was investigated at RNA level.

RESULTS

In each subject a heterozygous pathogenic variant in CBFB was detected, whereas no genomic alteration involving RUNX2 was found. Three CBFB variants (one splice site alteration, one nonsense variant, one 2 bp duplication) were shown to result in a premature stop codon. A large intragenic deletion was found to delete exon 4, without affecting CBFB expression. The effect of a second splice site variant could not be determined but most likely results in a shortened or absent protein. Affected individuals showed similarities with RUNX2-related CCD, including dental and clavicular abnormalities. Normal stature and neurocognitive problems were however distinguishing features. CBFB encodes the core-binding factor β subunit, which can interact with all RUNX proteins (RUNX1, RUNX2, RUNX3) to form heterodimeric transcription factors. This may explain the phenotypic differences between CBFB-related and RUNX2-related CCD.

CONCLUSION

We confirm the previously suggested locus heterogeneity for CCD by identifying five pathogenic variants in CBFB in a cohort of eight individuals with clinical and radiographic features reminiscent of CCD.

The prevalence of hypercapnia during acute infection in children on chronic noninvasive ventilation: A retrospective study

BACKGROUND/AIM

Children on chronic noninvasive ventilation are at risk for nonelective hospitalizations, mainly for acute infections. This study examined the prevalence of hypercapnia in children on chronic ventilatory support during an acute admission.

METHODS

This retrospective study included children aged 0 to 18 years who regularly used bilevel positive airway pressure or continuous positive airway pressure at home, and who were diagnosed with an acute infection, and were hospitalized at the pediatrics department or pediatric intensive care unit. Capillary blood gas analysis and parameters of the built-in software of the home ventilator were recorded.

RESULTS

Among the 43 cases included, hypercapnia was prevalent in 23% with a mean partial pressure of carbon dioxide of 51.7 ± 6.4 mm  Hg. These children also had lower oxygen saturation levels. The respiratory rate 48 hours before admission was significantly higher in the hypercapnic group and the volume guarantee mode was less frequently used in the hypercapnic group.

CONCLUSION

Approximately, a quarter of the cases of chronic home ventilation experience hypercapnia during an acute infection. Our data warrant a prospective study on the monitoring of respiratory rate in patients with chronic respiratory insufficiency as an indicator for hospitalizations with hypercapnia; we also recommend the use of volume guarantee mode of ventilation to prevent hypercapnia.