Delineation and Diagnostic Criteria of Oral-Facial-Digital Syndrome Type VI

Oral-Facial-Digital Syndrome type VI (OFD VI) represents a rare phenotypic subtype of Joubert syndrome and related disorders (JSRD). In the original report polydactyly, oral findings, intellectual disability, and absence of the cerebellar vermis at post-mortem characterized the syndrome. Subsequently, the molar tooth sign (MTS) has been found in patients with OFD VI, prompting the inclusion of OFD VI in JSRD. We studied the clinical, neurodevelopmental, neuroimaging, and genetic findings in a cohort of 16 patients with OFD VI. We derived the following inclusion criteria from the literature: 1) MTS and one oral finding and polydactyly, or 2) MTS and more than one typical oral finding. The OFD VI neuroimaging pattern was found to be more severe than in other JSRD subgroups and includes severe hypoplasia of the cerebellar vermis, hypoplastic and dysplastic cerebellar hemispheres, marked enlargement of the posterior fossa, increased retrocerebellar collection of cerebrospinal fluid, abnormal brainstem, and frequently supratentorial abnormalities that occasionally include characteristic hypothalamic hamartomas. Additionally, two new JSRD neuroimaging findings (ascending superior cerebellar peduncles and fused thalami) have been identified. Tongue hamartomas, additional frenula, upper lip notch, and mesoaxial polydactyly are specific findings in OFD VI, while cleft lip/palate and other types of polydactyly of hands and feet are not specific. Involvement of other organs may include ocular findings, particularly colobomas. The majority of the patients have absent motor development and profound cognitive impairment. In OFD VI, normal cognitive functions are possible, but exceptional. Sequencing of known JSRD genes in most patients failed to detect pathogenetic mutations, therefore the genetic basis of OFD VI remains unknown. Compared with other JSRD subgroups, the neurological findings and impairment of motor development and cognitive functions in OFD VI are significantly worse, suggesting a correlation with the more severe neuroimaging findings. Based on the literature and this study we suggest as diagnostic criteria for OFD VI: MTS and one or more of the following: 1) tongue hamartoma(s) and/or additional frenula and/or upper lip notch; 2) mesoaxial polydactyly of one or more hands or feet; 3) hypothalamic hamartoma

Pontine tegmental cap dysplasia: a novel brain malformation with a defect in axonal guidance

Four unrelated children are described with an identical brainstem and cerebellar malformation on MRI. The key findings are: vermal hypoplasia, subtotal absence of middle cerebellar peduncles, flattened ventral pons, vaulted pontine tegmentum, molar tooth aspect of the pontomesencephalic junction and absent inferior olivary prominence. Peripheral hearing impairment is present in all. Variable findings are: horizontal gaze palsy (1/4), impaired swallowing (2/4), facial palsy (3/4), bilateral sensory trigeminal nerve involvement (1/4), ataxia (2/4). Bony vertebral anomalies are found in 3/4. Additional MR studies in one patient using diffusion tensor imaging (DTI) with colour coding and fibre tracking revealed an ectopic transverse fibre bundle at the site of the pontine tegmentum and complete absence of transverse fibres in the ventral pons. The combined findings indicate an embryonic defect in axonal growth and guidance. Phenotypic analogy to mice with homozygous inactivation of Ntn1 encoding the secreted axonal guidance protein netrin1, or Dcc encoding its receptor Deleted in Colorectal Cancer led us to perform sequence analysis of NTN1 and DCC in all the patients. No pathogenic mutations were found. For the purpose of description the name 'pontine tegmental cap dysplasia' (PTCD) is proposed for the present malformation, referring to its most distinguishing feature on routine MR

Pontine tegmental cap dysplasia: a novel brain malformation with a defect

in axonal guidanc

tRNA splicing endonuclease mutations cause pontocerebellar hypoplasia

Pontocerebellar hypoplasias (PCH) represent a group of neurodegenerative autosomal recessive disorders with prenatal onset, atrophy or hypoplasia of the cerebellum, hypoplasia of the ventral pons, microcephaly, variable neocortical atrophy and severe mental and motor impairments. In two subtypes, PCH2 and PCH4, we identified mutations in three of the four different subunits of the tRNA-splicing endonuclease complex. Our findings point to RNA processing as a new basic cellular impairment in neurological disorders