Refinement of the 8q22.1 microdeletion critical region associated with Nablus mask-like facial syndrome

Atlantoaxial dislocation in the setting of NMLFS

BACKGROUND

Nablus mask-like facial syndrome (NMFLS) is an extremely rare genetic syndrome characterized by facial dysmorphia as well as developmental delay. In the present report we describe a potential association between non-traumatic atlanto-occipital dislocation and NMFLS in an 11-year old female lacking typical facial features of NMFLS.

CASE DESCRIPTION

An 11-year-old female with autism presented with symptoms of persistent headache and vomiting as well as neck stiffness. Further investigation and CT imaging revealed congenital malformation of the skull base and craniocervical junction with complete posterior subluxation of the left occipital condyle. MRI findings later corroborated the findings on CT.

CONCLUSIONS

The patient was successfully treated with occipitocervical fusion. The findings in this case suggest the possibility that atlanto-occipital instability and generalized occipitocervical may be associated with NMFLS.

Nablus Mask-Like Facial Syndrome with Moderate Developmental Delay

Nablus mask-like facial syndrome (NMLFS) is defined by distinctive craniofacial appearance including tight-appearing glistening facial skin, blepharophimosis, telecanthus, severe arched eyebrows, flat and broad nose, long philtrum, distinctive ears, unusual hair patterns, mild developmental delay and "happy" disposition. We aim to report a 7-year-old boy diagnosed with NMLFS and moderate developmental delay. Literature emphasis that Intellectual Disability is common in this syndrome though it has been diagnosed to only a few people worldwide.

Nablus syndrome: Easy to diagnose yet difficult to solve

Nablus syndrome was first described by the late Ahmad Teebi in 2000, and 13 individuals have been reported to date. Nablus syndrome can be clinically diagnosed based on striking facial features, including tight glistening skin with reduced facial expression, blepharophimosis, telecanthus, bulky nasal tip, abnormal external ear architecture, upswept frontal hairline, and sparse eyebrows. However, the precise genetic etiology for this rare condition remains elusive. Comparative microarray analyses of individuals with Nablus syndrome (including two mother-son pairs) reveal an overlapping 8q22.1 microdeletion, with a minimal critical region of 1.84 Mb (94.43-96.27 Mb). Whereas this deletion is present in all affected individuals, 13 individuals without Nablus syndrome (including two mother-child pairs) also have the 8q22.1 microdeletion that partially or fully overlaps the minimal critical region. Thus, the 8q22.1 microdeletion is necessary but not sufficient to cause the clinical features characteristic of Nablus syndrome. We discuss possible explanations for Nablus syndrome, including one-locus, two-locus, epigenetic, and environmental mechanisms. We performed exome sequencing for five individuals with Nablus syndrome. Although we failed to identify any deleterious rare coding variants in the critical region that were shared between individuals, we did identify one common SNP in an intronic region that was shared. Clearly, unraveling the genetic mechanism(s) of Nablus syndrome will require additional investigation, including genomic and RNA sequencing of a larger cohort of affected individuals. If successful, it will provide important insights into fundamental concepts such as variable expressivity, incomplete penetrance, and complex disease relevant to both Mendelian and non-Mendelian disorders.

A familial chromosomal complex rearrangement confirms RUNX1T1 as a causative gene for intellectual disability and suggests that 1p22.1p21.3 duplication is likely benign

Background

Complex chromosomal rearrangements are constitutive structural aberrations involving three or more breaks. They can be balanced or unbalanced and result in different outcomes, depending on deletion/duplication of genomic material, gene disruption, or position effects.

Case presentation

We report on a patient presenting with severe anemia, splenomegaly, mild intellectual disability and facial dysmorphisms harboring a 4.3 Mb duplication at 1p22.1p21.3 and a 2.1 Mb deletion at 8q21.3q22.1, involving RUNX1T1 gene. The healthy brother presented the same duplication of chromosome 1p as at 1p22.1p21.3.

Conclusions

The rearrangement found both these siblings resulted from malsegregation in the proband and recombination in her healthy brother of a balanced paternal complex chromosomal rearrangement. These results confirm RUNX1T1 as a causative gene for intellectual disability and suggest the 1p22.1p21.3 duplication is likely benign.