Delayed myelination in a patient with 18q- syndrome

Abnormal myelination in ring chromosome 18 syndrome

Partial deletion of genetic material from the long arm of chromosome 18 results in a syndrome with multisystemic involvement, including dysmorphic features, intellectual disability, cardiac malformations, endocrine abnormalities, immunodeficiency, musculoskeletal deformities, and variable neurologic manifestations. Hypomyelination has been reported in patients with chromosome 18q- and postulated to be secondary to deletion of the gene coding for myelin basic protein found at 18q23. Little however is reported on cerebral anomalies seen in patients with ring chromosome 18, an analogous syndrome but with expectedly more severe phenotype secondary to the combined deletions of genetic material from both the short (p-) and long arm (q-) of chromosome 18. We are reporting a case of a girl with ring chromosome 18 and deletions involving 18p11.32-18p11.21 and 18q21.31-18q23. The abnormalities observed on magnetic resonance imaging are discussed with a specific focus on the evolution and significance of associated white matter changes.

High-field (9.4 T) MRI of brain dysmyelination by quantitative mapping of magnetic susceptibility

The multilayered myelin sheath wrapping around nerve axons is essential for proper functioning of the central nervous system. Abnormal myelination leads to a wide range of neurological diseases and developmental disorders. Non-invasive imaging of myelin content is of great clinical importance. The present work demonstrated that loss of myelin in the central nervous system of the shiverer mouse results in a dramatic reduction of magnetic susceptibility in white matter axons. The reduction resulted in a near extinction of susceptibility contrast between gray and white matter. Quantitative magnetic susceptibility imaging and diffusion tensor imaging were conducted on a group of control and shiverer mice at 9.4 T. We measured the resonance frequency distribution of the whole brain for each mouse. Magnetic susceptibility maps were computed and compared between the two groups. It was shown that the susceptibility contrast between gray and white matter was reduced by 96% in the shiverer compared to the controls. Diffusion measurements further confirmed intact fiber pathways in the shiverer mice, ruling out the possibility of axonal injury and its potential contribution to the altered susceptibility. As an autosomal recessive mutation, shiverer is characterized by an almost total lack of central nervous system myelin. Our data provide new evidences indicating that myelin is the predominant source of susceptibility differences between deep gray and white matter observed in magnetic resonance imaging. More importantly, the present study suggests that quantitative magnetic susceptibility is a potential endogenous biomarker for myelination.

Mapping structural differences of the corpus callosum in individuals with 18q deletions using targetless regional spatial normalization

Individuals with a constitutional chromosome abnormality consisting of a deletion of a portion of the long arm of chromosome 18 (18q-) have a high incidence ( approximately 95%) of dysmyelination. Neuroradiologic findings in affected children report a smaller corpus callosum, but this finding has not been quantified. This is in part due to the large intersubject variability of the corpus callosum size and shape and the small number of subjects with 18q-, which leads to low statistical power for comparison with typically developing children. An analysis method called targetless spatial normalization (TSN) was used to improve the sensitivity of statistical testing. TSN converges all images in a group into what is referred as group common space. The group common space conserves common shape, size, and orientation while reducing intragroup variability. TSN in conjunction with a Witelson vertical partitioning scheme was used to assess differences in corpus callosum size between 12 children with 18q- and 12 age-matched normal controls. Significant global and regional differences in corpus callosum size were seen. The 18q- group showed an overall smaller (25%) corpus callosum (P < 10(-7)), even after correction for differences in brain size. Regionally, the posterior portions of corpus callosum (posterior midbody, isthmus, and splenium), which contain heavily myelinated fibers, were found to be 25% smaller in the population with 18q-.

Growth hormone benefits children with 18q deletions

Most individuals with constitutional deletions of chromosome 18q have developmental delays, dysmyelination of the brain, and growth failure due to growth hormone deficiency. We monitored the effects of growth hormone treatment by evaluating 23 individuals for changes in growth, nonverbal intelligence quotient (nIQ), and quantitative brain MRI changes. Over an average of 37 months, the treated group of 13 children had an average nIQ increase of 17 points, an increase in height standard deviation score of 1.7, and significant change in T1 relaxation times in the caudate and frontal white matter. Cognitive changes of this magnitude are clinically significant and are anticipated to have an effect on the long-term outcomes for the treated individuals.

18q? Syndrome: Brain MRI shows poor differentiation of gray and white matter on T2-weighted images

PURPOSE

To study brain MRI findings in patients with 18q- syndrome and to correlate these findings with the results of the molecular breakpoint analysis.

MATERIALS AND METHODS

Brain MR images of 17 patients with 18q- syndrome were evaluated. Segregation analysis was performed with 15 microsatellite markers to determine the deletion breakpoints and whether the deletion included the myelin basic protein (MBP) gene.

RESULTS

One patient had an interstitial deletion of 18q which spared the MBP gene. He was the only one with normal brain MRI. All 16 patients with deletions including the MBP gene had abnormal white matter in MRI. The main finding was poor differentiation of gray and white matter on T2-weighted images due to increased white matter signal intensity. In addition, measured signal intensity of the white matter was significantly increased in patients compared with controls.

CONCLUSIONS

Poor differentiation of gray and white matter on T2-weighted images is the most typical MRI finding of the 18q- syndrome. These results support the postulation that abnormal myelination in 18q- syndrome is due to haploinsufficiency at or near the MBP locus.

Molecular characterization of a patient with central nervous system dysmyelination and cryptic unbalanced translocation between chromosomes 4q and 18q

We report on a 12-year-old boy who presented with delayed development and CNS dysmyelination. Genetic studies showed a normal 46,XY karyotype by routine cytogenetic analysis, and 46,XY.ish del(18)(q23)(D18Z1+, MBP-) by FISH using a locus-specific probe for the MBP gene (18q23). Though the patient appeared to have normal chromosome 18s by repeated high resolution banding analysis, his clinical features were suggestive of a deletion of 18q. These included hearing loss secondary to stenosis of the external auditory canals, abnormal facial features, and foot deformities. FISH studies with genomic probes from 18q22.3 to 18qter confirmed a cryptic deletion which encompassed the MBP gene. In an attempt to further characterize the deletion, whole genome screening was conducted using array based comparative genomic hybridization (array CGH) analysis. The array CGH data not only confirmed a cryptic deletion in the 18q22.3 to 18qter region of approximately 7 Mb, it also showed a previously undetected 3.7 Mb gain of 4q material. FISH studies demonstrated that the gained 4q material was translocated distal to the 18qter deletion breakpoint. The 18q deletion contains, in addition to MBP, other known genes including CYB5, ZNF236, GALR1, and NFATC1, while the gained 4q material includes the genes FACL1 and 2, KLKB1, F11 and MTNR1A. The use of these combined methodologies has resulted in the first reported case in which array CGH has been used to characterize a congenital chromosomal abnormality, highlighting the need for innovative molecular cytogenetic techniques in the diagnosis of patients with idiopathic neurological abnormalities.

Abnormal myelination in a patient with deletion 14q11.2q13.1

A male carrying an interstitial deletion of chromosome 14, presumably del(14)(q11.2q13), and presenting with abnormal myelination on magnetic resonance imaging is described. The abnormal myelination was evidenced as a high-signal intensity on T(2)-weighted magnetic resonance imaging. The patient had severe neurologic signs, various dysmorphic features, and a marked microcephaly. To our knowledge, this case is the first patient reported with abnormal myelination and a deletion of chromosome 14.

Interstitial deletion of 14q, 46, XY, del (14) (q24.3q32.1) associated with status nonepileptic myoclonia and delayed myelination

A Japanese boy with interstitial deletion of the long arm of chromosome 14, including band 14q31, is described. The characteristic dysmorphic facial features, such as dolichocephaly, bushy eyebrows, horizontal narrow palpebral fissures, long philtrum, etc, and mental and motor developmental delay were observed. Other characteristic clinical manifestations were anuresis and status nonepileptic myoclonia The finding of delayed myelination of the cerebral white matter was observed on magnetic resonance examination, suggesting that an unknown factor related to myelination in the central nervous system might be localized in band 14q31.

Magnetic resonance imaging demonstrates incomplete myelination in 18q- syndrome: evidence for myelin basic protein haploinsufficiency

Magnetic resonance imaging (MRI) and MRI relaxometry were used to investigate disturbed brain myelination in 18q- syndrome, a disorder characterized by mental retardation, dysmorphic features, and growth failure. T1-weighted and dual spin-echo T2-weighted MR images were obtained, and T1 and T2 parametric image maps were created for 20 patients and 12 controls. MRI demonstrated abnormal brain white matter in all patients. White matter T1 and T2 relaxation times were significantly prolonged in patients compared to controls at all ages studied, suggesting incomplete myelination. Chromosome analysis using fluorescence in situ hybridization techniques showed that all patients with abnormal MRI scans and prolonged white matter T1 and T2 relaxation times were missing one copy of the myelin basic protein (MBP) gene. The one patient with normal-appearing white matter and normal white matter T1 and T2 relaxation times possessed two copies of the MBP gene. MRI and molecular genetic data suggest that incomplete cerebral myelination in 18q- is associated with haploinsufficiency of the gene for MBP.