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A Prospective Study of Neurological Abnormalities in Phelan-McDemid Syndrome

Background: Phelan-McDermid syndrome (PMS) occurs as a result of a chromosomal abnormality, most frequently deletion, in the long arm of chromosome 22, involving the SHANK3 gene. Our goal was to prospectively assess the neurological phenotype in this syndrome.

METHODS: Twenty-nine participants were recruited from ongoing studies in PMS at the Seaver Autism Center. They had a structured, uniform neurological examination performed by a pediatric neurologist (Y.F.). Abnormal findings were graded as mild, moderate or severe. In addition, reports of seizures, magnetic resonance imaging (MRI) and electroencephalograms (EEG) were reviewed. We calculated the frequency and severity of neurological abnormalities, as well as correlations between items on the neurological examination and items on the Mullen Scales
of Early Learning and on the Vineland Adaptive Behavioral Scales (VABS).

RESULTS: Hypotonia, abnormal gait, fine motor coordination deficits, and expressive and receptive language delays were present in all participants. Attention deficits were present in 96% (severe in 62%), and abnormal visual tracking was present in 86%. A history of seizures was obtained in 44.8% of participants but 46.1% of these were febrile only.

Of the 13 EEG reports available for review – 69.2% were abnormal- with epileptic features present in 53.8%.

Abnormalities were present in 62.5% of MRI reports. Correlations were found between neurological abnormalities and scores on the Mullen and Vineland Scales.

CONCLUSIONS: Neurological abnormalities are very common in PMS and are correlated with measures of cognitive and adaptive functioning. The neurological examination may be used for clinical diagnosis, identification of PMS phenotypes, and, in the future, for evaluation of therapy.