Phenotype of a Belgian Family With 6p25 Deletion Syndrome

Case report: Extending the spectrum of clinical and molecular findings in FOXC1 haploinsufficiency syndrome

FOXC1 is a ubiquitously expressed forkhead transcription factor that plays a critical role during early development. Germline pathogenic variants in FOXC1 are associated with anterior segment dysgenesis and Axenfeld-Rieger syndrome (ARS, #602482), an autosomal dominant condition with ophthalmologic anterior segment abnormalities, high risk for glaucoma and extraocular findings including distinctive facial features, as well as dental, skeletal, audiologic, and cardiac anomalies. De Hauwere syndrome is an ultrarare condition previously associated with 6p microdeletions and characterized by anterior segment dysgenesis, joint instability, short stature, hydrocephalus, and skeletal abnormalities. Here, we report clinical findings of two unrelated adult females with FOXC1 haploinsufficiency who have ARS and skeletal abnormalities. Final molecular diagnoses of both patients were achieved using genome sequencing. Patient 1 had a complex rearrangement involving a 4.9 kB deletion including FOXC1 coding region (Hg19; chr6:1,609,721-1,614,709), as well as a 7 MB inversion (Hg19; chr6:1,614,710-8,676,899) and a second deletion of 7.1 kb (Hg19; chr6:8,676,900-8,684,071). Patient 2 had a heterozygous single nucleotide deletion, resulting in a frameshift and a premature stop codon in FOXC1 (NM_001453.3): c.467del, p.(Pro156Argfs*25). Both individuals had moderate short stature, skeletal abnormalities, anterior segment dysgenesis, glaucoma, joint laxity, pes planovalgus, dental anomalies, hydrocephalus, distinctive facial features, and normal intelligence. Skeletal surveys revealed dolichospondyly, epiphyseal hypoplasia of femoral and humeral heads, dolichocephaly with frontal bossin gand gracile long bones. We conclude that haploinsufficiency of FOXC1 causes ARS and a broad spectrum of symptoms with variable expressivity that at its most severe end also includes a phenotype overlapping with De Hauwere syndrome.

The phenotypic spectrum of terminal and subterminal 6p deletions based on a social media-derived cohort and literature review

BACKGROUND

Terminal 6p deletions are rare, and information on their clinical consequences is scarce, which impedes optimal management and follow-up by clinicians. The parent-driven Chromosome 6 Project collaborates with families of affected children worldwide to better understand the clinical effects of chromosome 6 aberrations and to support clinical guidance. A microarray report is required for participation, and detailed phenotype information is collected directly from parents through a multilingual web-based questionnaire. Information collected from parents is then combined with case data from literature reports. Here, we present our findings on 13 newly identified patients and 46 literature cases with genotypically well-characterised terminal and subterminal 6p deletions. We provide phenotype descriptions for both the whole group and for subgroups based on deletion size and HI gene content.

RESULTS

The total group shared a common phenotype characterised by ocular anterior segment dysgenesis, vision problems, brain malformations, congenital defects of the cardiac septa and valves, mild to moderate hearing impairment, eye movement abnormalities, hypotonia, mild developmental delay and dysmorphic features. These characteristics were observed in all subgroups where FOXC1 was included in the deletion, confirming a dominant role for this gene. Additional characteristics were seen in individuals with terminal deletions exceeding 4.02 Mb, namely complex heart defects, corpus callosum abnormalities, kidney abnormalities and orofacial clefting. Some of these additional features may be related to the loss of other genes in the terminal 6p region, such as RREB1 for the cardiac phenotypes and TUBB2A and TUBB2B for the cerebral phenotypes. In the newly identified patients, we observed previously unreported features including gastrointestinal problems, neurological abnormalities, balance problems and sleep disturbances.

CONCLUSIONS

We present an overview of the phenotypic characteristics observed in terminal and subterminal 6p deletions. This reveals a common phenotype that can be highly attributable to haploinsufficiency of FOXC1, with a possible additional effect of other genes in the 6p25 region. We also delineate the developmental abilities of affected individuals and report on previously unrecognised features, showing the added benefit of collecting information directly from parents. Based on our overview, we provide recommendations for clinical surveillance to support clinicians, patients and families.

Chromosome 6p25 deletion syndrome: A case report and review of ophthalmic features

The 6p25 deletion syndrome is a rare genetic disorder characterized by a wide spectrum of congenital anomalies. Ophthalmic abnormalities appear to be highly associated with the syndrome, although this relationship has not been well characterized to date. We conducted a systematic literature review to highlight the ocular features in patients with this deletion syndrome and describe a 7-month-old female who has a 6.07 MB 6p25.1p25.3 deletion and a 4.25 MB 17q25.3 duplication. Our patient presented with multiple congenital anomalies, including macrocephaly, frontal bossing, low set ears, tent-shaped mouth, saddle nose, flat midface, and hearing impairment. Her ophthalmic features included proptosis, down-slanting palpebral fissures, hypertelorism, nystagmus, bilateral posterior embryotoxon, and decentered and abnormally shaped pupils. A systematic review of the published cases with sufficient clinical eye descriptions included 63 cases with a confirmed 6p25 deletion. The most common eye findings observed were posterior embryotoxon, iris hypoplasia, corectopia, cornea opacity, and glaucoma.

Case report: Congenital mitral and tricuspid valve insufficiency in a patient with Axenfeld-Rieger syndrome

Axenfeld-Rieger syndrome (ARS) is an autosomal dominant disorder that is primarily due to disruption of the development of neural crest cells. The onset of associated symptoms in both eyes accompanied by extraocular developmental defects is referred to as ARS. Cardiac defects associated with ARS have been reported, but the extent of the cardiac defects has yet to be defined. We report a case of a 17-year-old girl with ARS with typical facial malformations and severe mitral and tricuspid valve insufficiency. The patient was diagnosed with secondary glaucoma detected on ophthalmologic examination. Echocardiography showed severe mitral and tricuspid valve insufficiency. This case provides further evidence of the association of ARS with cardiac malformations and extends the reported range of cardiac malformations in patients with ARS.

Sensorineural hearing loss and hypoplastic cochlea in Axenfeld-Rieger syndrome with FOXC1 mutation

OBJECTIVE

Axenfeld-Rieger syndrome (ARS) type 3 is a rare autosomal dominant disease, characterized by anterior segment dysgenesis of the eye, hearing loss, and cardiac defects. ARS type 3 is highly associated with FOXC1 mutations, which induces developmental disorders of neural crest cells. Most studies about ARS patients focused on ophthalmologic findings, but details in their hearing loss have not yet been revealed. In this report, we investigated audiological and otological manifestations in the ARS type 3 patient who had the novel heterozygous FOXC1 mutation leading deletion at the forkhead DNA-binding domain.

METHODS AND RESULTS

Pure tone audiometry showed bilateral sensorineural hearing loss (SNHL) and audiological examinations confirmed that major dysfunctions existed in the cochlea, rather than the spiral ganglion neurons and the cochlear nerve. CT and MRI revealed the hypoplastic cochlea at both sides. Given that the 6p25 deletion syndrome, lacking one allele of the FOXC1 gene, shows similar, but more severe cochlear malformations than the present case, the FOXC1 mutations might contribute to the hypoplasia and dysfunctions in the cochlea.

CONCLUSION

To our knowledge, this is the first report demonstrating that the ARS type 3 patient with the FOXC1 mutation has the hypoplasia and dysfunctions in the cochlea, which results in bilateral SNHL.

Novel Phenotype of 6p25 Deletion Syndrome Presenting Juvenile Parkinsonism and Brain Calcification

BACKGROUND

Chromosome 6p25 deletion syndrome is a rare neurocristopathy with variable clinical features. The objective of the current study was to describe a novel phenotype for autosomal-dominant chromosome 6p25 deletion syndrome. The presentation included bilateral basal ganglia and subcortical calcifications and juvenile parkinsonism, resembling primary familial brain calcification.

METHODS

Phenotypic characterization, exome sequencing, and oligonucleotide array were carried out in the index family.

RESULTS

The index patient and her mother had a history of developmental delay, mild facial dysmorphism, Axenfield eye anomalies, slight intellectual disability, and subsequently developed levodopa-responsive parkinsonism in early adulthood. Brain-computed tomography showed bilateral basal ganglia and subcortical calcifications. Magnetic resonance imaging revealed diffuse white matter lesions. A ^99mTc TRODAT single-photon emission computed tomography scan revealed bilateral dopaminergic denervation. Whole-exome sequencing and oligonucleotide array-based comparative genomic hybridization revealed a 2.27-Mb chromosome 6pter-p24 deletion, which cosegregated within the family.

CONCLUSIONS

Our findings extended the current phenotypic spectrum of chromosome 6p25 deletion syndrome. © 2020 International Parkinson and Movement Disorder Society.

Childhood glaucoma genes and phenotypes: Focus on FOXC1 mutations causing anterior segment dysgenesis and hearing loss

Childhood glaucoma is an important cause of blindness world-wide. Eleven genes are currently known to cause inherited forms of glaucoma with onset before age 20. While all the early-onset glaucoma genes cause severe disease, considerable phenotypic variability is observed among mutations carriers. In particular, FOXC1 genetic variants are associated with a broad range of phenotypes including multiple forms of glaucoma and also systemic abnormalities, especially hearing loss. FOXC1 is a member of the forkhead family of transcription factors and is involved in neural crest development necessary for formation of anterior eye structures and also pharyngeal arches that form the middle ear bones. In this study we review the clinical phenotypes reported for known FOXC1 mutations and show that mutations in patients with reported ocular anterior segment abnormalities and hearing loss primarily disrupt the critically important forkhead domain. These results suggest that optimal care for patients affected with anterior segment dysgenesis should include screening for FOXC1 mutations and also testing for hearing loss.

Cerebral White Matter Lesions and Dysmorphisms: Signs Suggestive of 6p25 Deletion Syndrome-Literature Review

Deletion of the region including chromosome 6p25 has been defined as a syndrome, with more than 68 reported cases. Individuals affected by the syndrome exhibit variable findings, including developmental delay and intellectual disability, cardiac anomalies, dysmorphic features, and-less commonly-skeletal and renal malformations. Ocular and hearing abnormalities are the most notable presenting features. The region encompasses more than 15 genes, of which the FOX group is the most likely causal factor of the clinical manifestations. We report the case of a 2-year-old child with developmental delay, generalized hypotonia, facial dysmorphism, and anomalies involving malformations of the eyes, heart, teeth, and skeleton. The magnetic resonance imaging (MRI) of the child's brain displayed cerebral anomalies involving the white matter, perivascular spaces, and corpus callosum. Array-CGH (comparative genomic hybridization) analysis displayed a de novo partial deletion of the short arm of chromosome 6, extending 5.13 Mb from nt 407.231 to nt 5.541.179. In infancy, neuroradiologic findings of abnormalities in the cerebral white matter and other neurologic anomalies elsewhere in the brain, in association with dysmorphisms and malformations, are highly suggestive of the diagnosis of 6p25 deletion syndrome. When these anomalies are found, the syndrome must be included in the differential diagnosis of disorders affecting the cerebral white matter.