Craniofacial dysmorphology in Down syndrome is caused by increased dosage of Dyrk1a and at least three other genes

Down syndrome (DS), trisomy of human chromosome 21 (Hsa21), occurs in 1 in 800 live births and is the most common human aneuploidy. DS results in multiple phenotypes, including craniofacial dysmorphology, which is characterised by midfacial hypoplasia, brachycephaly and micrognathia. The genetic and developmental causes of this are poorly understood. Using morphometric analysis of the Dp1Tyb mouse model of DS and an associated mouse genetic mapping panel, we demonstrate that four Hsa21-orthologous regions of mouse chromosome 16 contain dosage-sensitive genes that cause the DS craniofacial phenotype, and identify one of these causative genes as Dyrk1a. We show that the earliest and most severe defects in Dp1Tyb skulls are in bones of neural crest (NC) origin, and that mineralisation of the Dp1Tyb skull base synchondroses is aberrant. Furthermore, we show that increased dosage of Dyrk1a results in decreased NC cell proliferation and a decrease in size and cellularity of the NC-derived frontal bone primordia. Thus, DS craniofacial dysmorphology is caused by an increased dosage of Dyrk1a and at least three other genes.

Time course of sutural width during the physiological growth from birth to adulthood: CT quantitative and qualitative evaluations of sutural arches

PURPOSE

We performed a retrospective qualitative and quantitative evaluation of the sutural changes during the physiological growth to define the age-related ossification stages of major and minor skull sutures or synchondroses.

METHODS

A total of 390 healthy subjects, examined for cranio-facial trauma and whose CT scans turned out to be normal, were clustered into homogenous age-matched groups ranged from birth to 90 years. High-resolution CT was used to assess the degree of sutural closure according to a 3-grade scoring system, the sutural pattern, the width, and the density of the gap calculated as the average of two or three ROIs along each suture/synchondrosis.

RESULTS

The identification of a definite pattern depended on the suture's type, the closure degree, and the width of the gap (p < 0.001). The interdigitation process was more intricate for most of vault sutures than the skull base sutures/synchondroses. Closing grades 1, 2, and 3 were associated to an identifiable sutural pattern and the cutoff value of 1.45 mm of the gap width allowed to detect an identifiable sutural pattern with the best combination of sensitivity (97%) and specificity (98%). Age and sutural closing degree were inversely related to gap width while positively related to the gap density (p < 0.001).

CONCLUSION

The sutural ossification is an age-related process, distinctive for each suture, and synchondrosis; it occurs neither according to a predefined order along sutural arches nor following a sequential distribution in the cranial fossae, and some sutures continued their growth process during lifetime.

Maturation of pelvic ossification centers on computed tomography in normal children

BACKGROUND

The pelvis is composed of three paired primary ossification centers: the pubis, the ischium and the ilium. During maturation, multiple secondary ossification centers can be seen in the synchondroses between these bones and in the pelvic apophyses. The fragmented appearance of these centers can be confused with pathology.

OBJECTIVE

To examine development of pelvic ossification centers by CT and determine normal appearance throughout childhood.

MATERIALS AND METHODS

Three pediatric radiologists reviewed 325 pelvic CT scans in children and young adults 5-18 years old and graded 6 pelvic ossification centers to evaluate maturational changes in critical structures.

RESULTS

Rate and progression of ossification and age at complete fusion vary with gender at the different ossification centers in the growing pelvis.

CONCLUSION

Knowledge of the normal CT appearance of ossification centers throughout childhood is important to differentiate the normal appearance from pathology.

Quantitative approach to the posterior cranial fossa and craniocervical junction in asymptomatic children with achondroplasia

PURPOSE

We propose an magnetic resonance imaging (MRI)-based quantitative morphovolumetric approach to the posterior cranial fossa (PCF) and craniocervical junction (CCJ) changes in achondroplastic patients investigating possible associations with ventriculomegaly and medullary compression.

METHODS

We analyzed MRI of 13 achondroplastic children not treated by surgery. 3D FSPGR T1-weighted images were used to analyze (1) PCF synchondroses; (2) PCF volume (PCFV), PCF brain volume (PCFBV), PCFV/PCFBV ratio, cerebellar volume, cerebrospinal fluid (CSF) spaces volume, and IV ventricle volume; (3) PCF (clivus, supraocciput, exocciput lengths, tentorial angle) and CCJ (AP and LL diameters of foramen magnum (FM)) morphometry; (4) measurements of FM and jugular foramina (JF) areas; and (5) supratentorial ventricular volume.

RESULTS

All patients showed synostosis of spheno-occipital synchondroses, eight showed synostosis of intra-occipital synchondroses, nine showed CCJ impingement on the cervical cord but only three had cervical myelopathy. Compared to controls, clivus and exocciput lengths, LL and AP diameters of FM, FM area and JF area were significantly reduced, supraocciput length, tentorial angle, PCFV, PCFBV, cerebellar volume, supratentorial ventricular system volume were significantly increased. A correlation was found between clivus length and supratentorial ventricular volume, premature closure of intra-occipital synchondroses and FM area while a trend was found between FM area and supraocciput length.

CONCLUSION

Our analysis demonstrates a relationship between the shortening of the clivus and the ventriculomegaly. On the other hand the premature closure of PCF synchondroses, the shape, and the growth direction of supraocciput bone contribute to reduce the FM area, causing in some patients medullary compression.