Longitudinal assessment of cognitive characteristics in Costello syndrome

Abstract

Costello syndrome encompasses pre- and postnatal medical problems including polyhydramnios, failure to thrive, cardiac complications, and an increased risk for solid tumors. Hypotonia and developmental delay are typical in infancy, and mental retardation can be diagnosed in older patients. Previous studies on the cognitive development in Costello syndrome relied on clinically diagnosed cases. The recent discovery of heterozygous HRAS mutations allows for molecular confirmation of the clinical diagnoses. We report here on cognitive abilities and adaptive behavior in the first cohort of patients with molecularly confirmed diagnoses. Further, this is the first longitudinal assessment of cognitive function in this patient population. Sixteen patients with identified HRAS mutations were tested, and 14 completed the Leiter International Performance Scale-Revised. The mean Full-Scale IQ score of 57 (range 30-87) was within the range of mild Mental Retardation. Analysis of test component subsets showed a relative strength in Fluid Reasoning with a mean score of 69 (range 48-98), in the mild range of Mental Retardation. Longitudinal analysis was performed for 12 patients by comparison of data obtained at the first evaluation (T1) to results obtained 2 years later (T2). In these patients intellectual and language abilities remained stable, and no deterioration was seen. We have thus shown that Costello syndrome is a static condition regarding intellectual and language abilities. The Leiter-R Memory Screen indicated functioning in the mildly delayed range for the majority of patients. Adaptive behavior was evaluated using the Vineland tool, and longitudinal data comparison for adaptive behavior showed improvements in Daily Living Skills, Communication, and the Adaptive Behavior Composite. However, these results must be interpreted cautiously as the measuring tool was updated from T1 to T2. Receptive language skills were measured with the Peabody Picture Vocabulary Test-III, showing a mean receptive vocabulary standard score of 65 (SD 15) in the Extremely Low range. Expressive language skills, as measured by the Expressive Vocabulary Test (EVT), scored a mean of 51 (SD 14), in the Extremely Low range. However, half of the subjects obtained the lowest possible score on the EVT, demonstrating that this is not the ideal tool for use in this patient population.