Clinical conundrums in fragile X syndrome

Social Approach and Autistic Behavior in Children with Fragile X Syndrome

Social avoidance is a core phenotypic characteristic of fragile X syndrome (FXS) that has critical cognitive and social consequences. However, no study has examined modulation of multiple social avoidant behaviors in children with FXS. In the current study, we introduce the Social Approach Scale (SAS), an observation scale that includes physical movement, facial expression, and eye contact approach behaviors collected across multiple time points. Our findings suggested that social approach behaviors in children with FXS were affected by age, gender, setting, and time spent with an examiner. Selected social approach behaviors were related to autistic behavior. Increased eye contact over the course of a research assessment, in particular, was found to be a strong predictor of lower autistic behavior.

Charcot-Marie-Tooth disease type 1 and 2-an immunohistochemical study of muscle fibre cytoskeletal proteins and a marker for muscle fibre regeneration

In 10 patients with Charcot-Marie-Tooth disease type 1 (CMT1), hereditary motor and sensory neuropathy (HMSN) type 1, demyelinating form, and 10 patients with CMT2, HMSN type 2, axonal form, monoclonal antibodies directed against dystrophin, spectrin, desmin, vimentin and a myoblast and satellite-cell related antigen, Leu-19, were applied to muscle biopsies from the anterior tibial muscle. Data from the biopsies were compared with those from 20 age- and sex-matched healthy controls. Both CMT1 and CMT2 patients had normal stainings for dystrophin and spectrin, indicating a normal muscle fibre cytoskeletal structure. In the CMT2 group, seven patients had increased staining for desmin in the majority of the atrophic fibres. In the CMT1 group, six of the patients had a normal desmin staining in normal sized and in atrophic muscle fibres, while the remaining four patients had an increased staining for a desmin in a few atrophic muscle fibres. Seven CMT2 patients and one CMT1 patient had increased staining of vimentin in some atrophic muscle fibres. In contrast to CMT1 patients, all CMT2 patients had an increased staining for Leu-19 in a majority of the atrophic muscle fibres. These immunohistochemical data support earlier findings of muscle fibre histopathological differences in CMT1 and CMT2 patients, possible reflecting different pathophysiological mechanisms in the two disorders. Copyright 1998 Lippincott Williams & Wilkins

Investigation of peripheral neuropathy

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High functioning fragile X males: demonstration of an unmethylated fully expanded FMR-1 mutation associated with protein expression

Fragile X (fra(X)) males with a standardized IQ score of 70 or higher represent a high functioning (HF) or nonretarded fra(X) male group. This group, which does not include nonpenetrant males, has received little research attention to date. Of 221 fra(X) males who had been evaluated through The Children's Hospital in Denver since 1981 and had completed cognitive or developmental testing, 29 (13%) were high functioning by the above definition. We found that HF males on the whole had a lower cytogenetic score and were younger than retarded fra(X) males, but there was no difference between these two groups in the number of typical fra(X) physical manifestations present. FMR-1 DNA testing was performed on 134 fra(X) males and methylation status was determined for 51 of these. A greater percentage of HF males had a mosaic pattern or an incompletely methylated full mutation than did retarded males. A unique DNA pattern, an unmethylated fully expanded mutation, was discovered in 3 of the highest functioning fra(X) males. Protein studies performed on 2 of these males demonstrated the presence of FMR-1 protein, albeit at lower levels than normal. FMR-1 protein was not present in retarded fra(X) males. Significant FMR-1 protein expression may be responsible for higher cognitive functioning in the 2 males with unmethylated fully expanded mutations compared to retarded fra(X) males.

Evaluation of school children at high risk for fragile X syndrome utilizing buccal cell FMR-1 testing

We describe a pilot project utilizing saliva to identify the FMR-1 mutation in high-risk special education students from four public school districts in Colorado. The program included presentations to special education teachers regarding fragile X syndrome, parental consent for testing, completion of a behavior checklist by the teachers, identification of special education students at high risk for fragile X syndrome, subsequent brief examination of face and hands, collection of a saliva sample by either Gatorade swish or brushing of the inside of the cheek, and analysis for the FMR-1 mutation by PCR. Equivocal samples were studied by direct DNA testing using Southern blot analysis, and abnormal results were confirmed by a blood analysis for the FMR-1 mutation. Mutant individuals received genetic counseling and medical and educational assessments to optimize treatment and intervention. This pilot project was met with enthusiasm by the schools. Of the first 439 students evaluated, 68% were male with an average age of 7.75 years; 13% were mentally retarded or autistic. Most students referred for the evaluation were learning disabled (51%) and/or had an Attention Deficit Hyperactivity Disorder (ADHD) (35%). The overall prevalence of the FMR-1 mutation was 5 of 439 or 1.1%. This relatively low yield is probably due to the high number of non-retarded but learning disabled students tested. Of the mentally retarded patients tested, 3.5% were positive for the FMR-1 mutation; however, of the non-retarded or learning disabled patients, only 0.79% were FMR-1 positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Trinucleotide repeats and genome variation

The recent cloning of several disease genes has identified the instability of trinucleotide repeats as a fundamental mechanism for variation within the human genome. This mutation mechanism explains the unique inheritance characteristics of the diseases it causes, and there is a significant potential that this mechanism is involved in the pathogenesis of other, as yet uncharacterized, genetic diseases.