Heterozygous KIF1A variants underlie a wide spectrum of neurodevelopmental and neurodegenerative disorders

BackgroundDominant and recessive variants in the KIF1A gene on chromosome 2q37.3 are associated with several phenotypes, although only three syndromes are currently listed in the OMIM classification: hereditary sensory and autonomic neuropathy type 2 and spastic paraplegia type 30, both recessively inherited, and mental retardation type 9 with dominant inheritance.MethodsIn this retrospective multicentre study, we describe the clinical, neuroradiological and genetic features of 19 Caucasian patients (aged 3–65 years) harbouring heterozygous KIF1A variants, and extensively review the available literature to improve current classification of KIF1A-related disorders.ResultsPatients were divided into two groups. Group 1 comprised patients with a complex phenotype with prominent pyramidal signs, variably associated in all but one case with additional features (ie, epilepsy, ataxia, peripheral neuropathy, optic nerve atrophy); conversely, patients in group 2 presented an early onset or congenital ataxic phenotype. Fourteen different heterozygous missense variants were detected by next-generation sequencing screening, including three novel variants, most falling within the kinesin motor domain.ConclusionThe present study further enlarges the clinical and mutational spectrum of KIF1A-related disorders by describing a large series of patients with dominantly inherited KIF1A pathogenic variants ranging from pure to complex forms of hereditary spastic paraparesis/paraplegias (HSP) and ataxic phenotypes in a lower proportion of cases. A comprehensive review of the literature indicates that KIF1A screening should be implemented in HSP regardless of its mode of inheritance or presentations as well as in other complex neurodegenerative or neurodevelopmental disorders showing congenital or early onset ataxia.

Van der Knaap disease

Van der Knaap disease is a rare form of leukodystrophy, phenotypically characterized by megalencephaly, early-onset ataxia, pyramidal features, cognitive impairment, with an autosomal recessive inheritence. MRI Brain shows T1 and FLAIR hypointense subcortical cysts in mostly temporal lobes and in fronto-parietal subcortical areas. Authors report a 20 yr. girl with typical features.

Clinical Assessment of Dysarthria in Children with Cerebellar Syndrome Associated with PMM2-CDG

Phosphomannomutase deficiency (PMM2-CDG) causes a cerebellar syndrome that has been evaluated using the International Cooperative Ataxia Rating Scale (ICARS). However, no particular dysarthria tests have been used. Speech ICARS subscore subjectively assesses fluency and clarity of speech with two items. Repetition of syllables, traditionally used for characterization of ataxic speech, was validated in early-onset ataxia conditions. We assess the validity of the PATA test (SCA Functional Index [SCAFI]) in PMM2-CDG patients.PATA rates from 20 patients were compared with a control population were and correlated with ICARS and neuroimaging.There was a difference between the PATA rate in patients and controls. PATA rate increased with age in controls. In patients, the improvement of PATA rate with age was not significant. In patients, the PATA rate was negatively correlated with the total ICARS score and the Speech ICARS subscore. Regarding neuroimaging, midsaggital vermis relative diameter was positively correlated with PATA results. These last differences were also significant when the results are corrected by age.PATA rate provides an easy measure for a quantitative assessment of dysarthria that may help clinicians to monitor patients' evolution in a regular consultation. It could also be used in PMM2-CDG clinical trials implementing ICARS speech subscore information.