Neurologic phenotypes associated with COL4A1/ 2 mutations: Expanding the spectrum of disease

Abstract

Objective: To characterize the neurologic phenotypes associated with COL4A1/2 mutations and to seek genotype-phenotype correlation.

Methods: We analyzed clinical, EEG, and neuroimaging data of 44 new and 55 previously reported patients with COL4A1/COL4A2 mutations.

Results: Childhood-onset focal seizures, frequently complicated by status epilepticus and resistance to antiepileptic drugs, was the most common phenotype. EEG typically showed focal epileptiform discharges in the context of other abnormalities, including generalized sharp waves or slowing. In 46.4% of new patients with focal seizures, porencephalic cysts on brain MRI colocalized with the area of the focal epileptiform discharges. In patients with porencephalic cysts, brain MRI frequently also showed extensive white matter abnormalities, consistent with the finding of diffuse cerebral disturbance on EEG. Notably, we also identified a subgroup of patients with epilepsy as their main clinical feature, in which brain MRI showed nonspecific findings, in particular periventricular leukoencephalopathy and ventricular asymmetry. Analysis of 15 pedigrees suggested a worsening of the severity of clinical phenotype in succeeding generations, particularly when maternally inherited. Mutations associated with epilepsy were spread across COL4A1 and a clear genotype-phenotype correlation did not emerge.

Conclusion: COL4A1/COL4A2 mutations typically cause a severe neurologic condition and a broader spectrum of milder phenotypes, in which epilepsy is the predominant feature. Early identification of patients carrying COL4A1/COL4A2 mutations may have important clinical consequences, while for research efforts, omission from large-scale epilepsy sequencing studies of individuals with abnormalities on brain MRI may generate misleading estimates of the genetic contribution to the epilepsies overall.

Figure 1. The spectrum of imaging abnormalities observed with COL4A1 mutations

(A) Ventricular enlargement (arrows) and dysmorphism (dotted arrow), thinning of corpus callosum (*), white matter loss (patient 1). (B) Periventricular leukoencephalopathy (arrows) (patient 33/a). (C) Acute germinal matrix hemorrhage on fetal brain MRI (arrows) and consequent extensive leukoencephalopathy on postnatal brain MRI (*) at 8 days of life (patient 33/c). (D) Malformations of cortical development: porencephaly with schizencephalic cleft (dotted lines) and polymicrogyria (arrows) (patient 17). (E) Dysmorphism and asymmetry of basal ganglia (patient 30). (F) Porencephaly (patient 17).

Figure 2. Neuropathologic evaluation of vascular pathology and blood–brain barrier integrity

(A–D) Immunostaining with smooth muscle a-actin (SMA) shows no disruption or loss of vascular smooth muscle cells. More numerous SMA-immunopositive blood vessels in white matter were observed in the COL4A1 case (no. 1) (B) than in the control case (A). SMA expression in the COL4A1 case was not restricted to vascular arterioles (C) but was also observed in numerous vascular capillaries (D). (E–H) Evaluation of blood–brain barrier integrity using immunoglobulin G (IgG) immunostaining. More marked IgG–immunopositive small vessel permeability was observed in the COL4A1 case (F) than in the control case (E). Strong IgG immunolabeling was observed in processes with glial morphology, but not in neurons in the COL4A1 case (G, H). (I–P) Integrity of basal membrane. (I–L) Laminin immunolabeling was present in arterioles and in capillaries with homogenous thickness in both the control (I) and the COL4A1 case (J–L). (M–P) Expression of the COL4A1 protein. A regular pattern of immunolabelling in arterioles and capillaries presenting homogenous thickness was observed in the control case (M) and the COL4A1 case (N–P). Scale bar (A, B, I–K, M–O) = 100 µm; (C, H) = 20 µm; (D, G, L, P) = 50 µm; (E, F) = 200 µm.

Figure 3. The distribution of mutations in the genes

The upper half of each figure depicts missense mutations, the lower half frameshift and splice-site mutations. (A) Distribution of COL4A1 mutations. (B) Distribution of COL4A2 mutations.

Figure 4. MRI findings in a pedigree (cases 33a–33e) with COL4A1 mutation (p.G1369R)

wt/m = wild-type/mutated.