Correlates of mental retardation and structural changes of the brain

From fossil to fetus: nonhemorrhagic germinal matrix echodensity caused by mineralizing vasculitis--hypothesis of fossilizing germinolysis and gliosis

Subventricular echodensities medioventral to the caudate nucleus near the caudothalamic groove are regular ultrasonographic findings in preterm infants with germinal matrix hemorrhages. The transformation into pseudocysts is termed germinolysis. Interestingly, identical ultrasonographic findings are rarely even reported for near-term infants. We examined 5 cases of near-term infants presenting with various localized subventricular echodensities after various noncerebral infections (intra-amniotic infection, gastroenteritis of unidentified pathogens, septic wound, and a twin pair with rotavirus gastroenteritis), suggesting an inflammatory or ischemic rather than a hemorrhagic etiology. With high-resolution ultrasonography, these lesions showed similar characteristics: all were space-occupying, homogeneous, echodense, and ultimately transformed into pseudocysts. Additionally, Doppler ultrasonography showed linear perivascular echodensities in the basal ganglia of one infant. All infants were also examined by cerebral magnetic resonance imaging (MRI) including T2*-weighted gradient-echo sequences so that subventricular hemorrhages could be excluded in 4 infants. One of these 4 infants died unexpectedly at home. Brain autopsy revealed nonhemorrhagic germinal matrix pseudocysts with gliotic walls. Based on our findings and the original literature, we favored an ischemic infarction of the strongly vascularized and highly metabolic germinal matrix as cause of this germinolysis and gliosis. We postulated that the infarction was the result of an obstructive and possibly mineralizing, or even fossilizing vasculopathy due to an inflammatory response. The precise pathogenesis of the suspected immune-mediated vasculitis remains unknown. We concluded that cerebral ultrasonography should be performed in infants with noncerebral infection and that it should be complemented by MRI in cases of subventricular echodensities to prove or to exclude a germinal matrix hemorrhage.

Trisomy 21 and the brain

In fetuses with Down syndrome, neurons fail to show normal dendritic development, yielding a "tree in winter" appearance. This developmental failure is thought to result in mental retardation. In adults with Down syndrome, neuronal loss is dramatic and neurofibrillary and neuritic Abeta plaque pathologies are consistent with Alzheimer disease. These pathological changes are thought to underlie the neuropsychological and physiological changes in older individuals with Down syndrome. Two chromosome 21-based gene products, beta-amyloid precursor protein (betaAPP) and S100B, have been implicated in these neuronal and interstitial changes. Although not necessary for mental retardation and other features, betaAPP gene triplication is necessary, although perhaps not sufficient, for development of Alzheimer pathology. S100B is overexpressed throughout life in Down patients, and mice with extra copies of the S100B gene have dendritic abnormalities. S100B overexpression correlates with Alzheimer pathology in post-adolescent Down syndrome patients and has been implicated in Abeta plaque pathogenesis. Interleukin-1 (IL-1) is a non-chromosome-21-based cytokine that is also overexpressed throughout life in Down syndrome. IL-1 upregulates betaAPP and S100B expression and drives numerous neurodegenerative and self-amplifying cascades that support a neuroinflammatory component in the pathogenesis of sporadic and Down syndrome-related Alzheimer disease.

Neurometabolic testing in developmental delay

The goal of this study was to examine the usefulness of neurometabolic testing in patients with unexplained developmental delay. We included 118 patients from ages 3 months to 13 years. The evaluation was conducted according to a protocol that called for stepwise investigations with the intention to minimize unnecessary tests. Clinical and neuroradiologic abnormalities were used as guidelines for the type and extent of the neurometabolic work-up. Based on our results, a diagnosis for a neurometabolic disorder was established in 16 patients (13.6%). Findings regarding abnormal metabolites (amino acids, ammonia, lactate, pyruvate, urine organic acids) did not lead to a diagnosis but to further investigations. Abnormalities in lysosomal enzymes, very-long-chain fatty acids, and urine mucopolysaccharides were definitive in establishing a diagnosis. In conclusion, in children with slowly progressing development with no apparent cause, there is a need for guidelines regarding the type of patients who need to be tested and the kind and extent of neurometabolic diagnostic work-up.

Prenatal hypoxia-ischemia alters expression and activity of nitric oxide synthase in the young rat brain and causes learning deficits

Inhibition of nitric oxide synthase (NOS) is known to possibly impair learning and memory. Our previous studies have demonstrated that prenatal hypoxia-ischemia (HI) decreases NOS expression and NOS activity in the neonatal rat brain. To investigate whether effects of prenatal HI on NOS expression continue and whether prenatal HI affects learning and memory in young rats, NOS expression and NOS activity were determined in the hippocampus of rat brains at 28 days of age following a prenatal HI insult on G17. Performances in the passive avoidance test and the Morris water maze test were also studied in these young rats prior to sampling. Rat fetuses were subjected to either a 30-min prenatal HI insult or a sham operation (SH) on gestation day 17 and rat pups were delivered naturally. Increased locomotor activity was observed in the prenatal HI rats as compared to the SH rats on postnatal days 13 and 15, but not on postnatal days 20 and 30. Prenatal HI affected learning ability in these young rats at 28 days of age, as indicated by a delayed acquisition of passive avoidance and by longer escape latency in the Morris water maze test as compared to the SH group. Prenatal HI did not affect retention of passive avoidance and spatial memory. Concomitant with these learning deficits, expression of neuronal NOS and endothelial NOS mRNAs as well as Ca2(+)-dependent NOS activity in the hippocampus of the prenatal HI rat brain were significantly decreased as compared to the SH group. These results suggest that a 30-min prenatal HI insult on gestation day 17 in rats has long-lasting effects on NOS expression and NOS activity in the offspring brain and on learning ability of these young rats. The learning deficit in offspring is possibly associated with the reduction in expression of NOS mRNA and NOS activity in the hippocampus of these animals.

Mental retardation: genetic findings, clinical implications and research agenda

The most important genetic advances in the field of mental retardation include the discovery of the novel genetic mechanism responsible for the Fragile X syndrome, and the imprinting involved in the Prader-Willi and Angelman syndromes, but there have also been advances in our understanding of the pathogenesis of Down syndrome and phenylketonuria. Genetic defects (both single gene Mendelizing disorders and cytogenetic abnormalities) are involved in a substantial proportion of cases of mild as well as severe mental retardation, indicating that the previous equating of severe mental retardation with pathology, and of mild retardation with normal variation, is a misleading over-simplication. Within the group in which no pathological cause can be detected, behaviour genetic studies indicate that genetic influences are important, but that their interplay with environmental factors, which are also important, is at present poorly understood. Research into the joint action of genetic and environmental influences in this group will be an important research area in the future.

Transient bifrontal solitary periventricular cysts in term neonates

We describe three children born at term investigated for neonatal seizures or transient apnoea. Cranial ultrasound and MRI unexpectedly revealed symmetrical periventricular cysts adjacent to the anterior horns. We found no evidence of prenatal viral infection, intraventricular or subependymal haemorrhage or hypoxic-ischaemic lesions. The lesions were not seen on MRI at 3 months of age, but there was no compensatory dilatation of the anterior horns nor secondary loss of white matter. The appearance and location of these transient cysts were different from those of the cystic changes which typically follow germinal matrix haemorrhage or periventricular leukomalacia. Their pathogenesis and clinical significance remain to be determined.