GFAP mutations, age at onset, and clinical subtypes in Alexander disease

OBJECTIVE

To characterize Alexander disease (AxD) phenotypes and determine correlations with age at onset (AAO) and genetic mutation. AxD is an astrogliopathy usually characterized on MRI by leukodystrophy and caused by glial fibrillary acidic protein (GFAP) mutations.

METHODS

We present 30 new cases of AxD and reviewed 185 previously reported cases. We conducted Wilcoxon rank sum tests to identify variables scaling with AAO, survival analysis to identify predictors of mortality, and χ(2) tests to assess the effects of common GFAP mutations. Finally, we performed latent class analysis (LCA) to statistically define AxD subtypes.

RESULTS

LCA identified 2 classes of AxD. Type I is characterized by early onset, seizures, macrocephaly, motor delay, encephalopathy, failure to thrive, paroxysmal deterioration, and typical MRI features. Type II is characterized by later onset, autonomic dysfunction, ocular movement abnormalities, bulbar symptoms, and atypical MRI features. Survival analysis predicted a nearly 2-fold increase in mortality among patients with type I AxD relative to those with type II. R79 and R239 GFAP mutations were most common (16.6% and 20.3% of all cases, respectively). These common mutations predicted distinct clinical outcomes, with R239 predicting the most aggressive course.

CONCLUSIONS

AAO and the GFAP mutation site are important clinical predictors in AxD, with clear correlations to defined patterns of phenotypic expression. We propose revised AxD subtypes, type I and type II, based on analysis of statistically defined patient groups.

Rasmussen encephalitis associated with Parry-Romberg syndrome

Parry-Romberg syndrome is a rare disorder associated with unilateral facial atrophy involving skin, subcutaneous tissue, skeletal muscle, and bone. Occasionally, there is CNS involvement with epilepsy being the most common CNS manifestation. The authors report a child with Parry-Romberg syndrome with a course strongly suggestive of Rasmussen encephalitis. The boy underwent hemispherectomy, and pathology showed the typical findings of Rasmussen encephalitis, suggesting that these two conditions may share common etiologic factors.

The mechanism of iron release from transferrin. Slow-proton-transfer-induced loss of nitrilotriacetatoiron(III) complex in acidic media

The role of protonation of amino acid ligands involved in iron release from human serum transferrin, previously saturated with nitrilotriacetatoiron(III) complex, has been elucidated in acidic media. Iron loss occurs first from the N-terminal site at pH < 6 and is followed at pH < 4 by iron release from the C-terminal iron-binding site. Nitrilotriacetatoiron(III) release from the N-terminal site is controlled by the slow protonation of the mixed protein/nitrilotriacetatoiron(III) complex; the second-order rate constant was k3a = 9.95 +/- 0.35 x 10(4) M-1.s-1. Protonation of an amino acid ligand in the C-terminal site leads to a new protein-site-C-loaded mixed complex with dissociation constant K4 = 0.300 +/- 0.025 mM. Nitrilotriacetatoiron(III) release is the result of mixed complex dissociation and the slow rate-limiting protonation of the iron-free protein with a proton dissociation constant K5a = 0.100 +/- 0.010 mM and a second-order rate constant k5a = 4.20 +/- 0.40 x 10(3) M-1.s-1. The mechanism of iron uptake and release seems to imply that slow proton transfers can induce complex formation between iron and the amino acid ligands of each of the protein iron-binding sites. These slow proton transfers may be controlled by the change of conformation of the binding sites upon iron loss.