Identification of a mosaic MTOR variant in purified neuronal DNA in a patient with focal cortical dysplasia using a novel depth electrode harvesting technique

OBJECTIVE

Recent studies have identified brain somatic variants as a cause of focal epilepsy. These studies relied on resected tissue from epilepsy surgery, which is not available in most patients. The use of trace tissue adherent to depth electrodes used for stereo electroencephalography (EEG) has been proposed as an alternative but is hampered by the low cell quality and contamination by nonbrain cells. Here, we use our improved depth electrode harvesting technique that purifies neuronal nuclei to achieve molecular diagnosis in a patient with focal cortical dysplasia (FCD).

METHODS

Depth electrode tips were collected, pooled by brain region and seizure onset zone, and nuclei were isolated and sorted using fluorescence-activated nuclei sorting (FANS). Somatic DNA was amplified from neuronal and astrocyte nuclei using primary template amplification followed by exome sequencing of neuronal DNA from the affected pool, unaffected pool, and saliva. The identified variant was validated using droplet digital polymerase chain reaction (PCR).

RESULTS

An 11-year-old male with drug-resistant genetic-structural epilepsy due to left anterior insula FCD had seizures from age 3 years. Stereo EEG confirmed seizure onset in the left anterior insula. The two anterior insula electrodes were combined as the affected pool and three frontal electrodes as the unaffected pool. FANS isolated 140 neuronal nuclei from the affected and 245 neuronal nuclei from the unaffected pool. A novel somatic missense MTOR variant (p.Leu489Met, CADD score 23.7) was identified in the affected neuronal sample. Droplet digital PCR confirmed a mosaic gradient (variant allele frequency = .78% in affected neuronal sample; variant was absent in all other samples).

SIGNIFICANCE

Our findings confirm that harvesting neuronal DNA from depth electrodes followed by molecular analysis to identify brain somatic variants is feasible. Our novel method represents a significant improvement compared to the previous method by focusing the analysis on high-quality cells of the cell type of interest.

Neonatal lead poisoning from maternal pica behavior during pregnancy

Lead toxicity has gained increasing attention in the public media because of its ubiquitous distribution in the environment and the potentially serious medical complications that it can induce, particularly in children. We present a case of an asymptomatic Hispanic woman who exhibited a unique form of pica during her pregnancy. By serendipity, she agreed to enroll into a lead screening study at our medical center when she presented to deliver her child. Her blood lead level was 119.4 microg/dL at delivery, and simultaneous measurement of the neonate's cord blood lead level was 113.6 microg/dL. The infant underwent an exchange transfusion, and the mother was treated with oral 2,3-dimercaptosuccinic acid. Both demonstrated dramatic biochemical improvement.

The lead content of blood serum

Serum lead concentrations measured by stable isotope dilution with a thermal ionization mass spectrometer and blood lead concentrations measured by graphite furnace atomic absorption spectrophotometry are reported for 73 women of child bearing age resident in Los Angeles, California. The two quantities are related by the line y=0.00030+0.00241x (r=0.83), where y is serum lead concentration and x is blood lead concentration, both being expressed in units of microg/L. The linearity of the relationship appears to hold to a blood lead concentration of at least 60 microg Pb/L. The slope of the line indicates that lead in serum is 0.24% of that in whole blood in contrast to recent reports of between 0.32 and 0.35% determined by inductively coupled plasma (ICP) mass spectrometry with bismuth used as an internal standard. The discrepancy stems from the ICP mass spectrometer-generated curves not passing through the origin.

The Effects of Retained Lead Bullets on Body Lead Burden

BACKGROUND

Numerous case reports have demonstrated that lead poisoning with potentially fatal consequences can result from retained lead projectiles after firearm injuries. To assess the impact of retained projectiles on subsequent lead exposure in the population, one cannot rely on self-selected cases presenting with symptoms of lead intoxication. This preliminary study seeks to identify increased lead burden and identify risk factors of elevated blood lead levels for individuals with retained lead bullets.

METHODS

Forty-eight patients were originally recruited from gunshot victims presenting for care at the King/Drew Medical Center in Los Angeles, California. An initial blood level was measured for all recruited patients and repeated for the 28 participants available for follow-up, 1 week to 8 months later. Medical history, including a history of prior firearm injuries and other retained projectiles, was taken, along with a screening and risk factor questionnaire to determine other sources of lead (occupational/recreational) to which the patient might have been, or is at present, exposed. The participants also had K-shell x-ray fluorescence determinations of bone lead in the tibia and calcaneus in order to determine past lead exposures not revealed by medical history and risk factor questionnaire. Multivariate models of blood level were made using risk factor and bone lead concentration data.

RESULTS

We demonstrated that blood lead tends to increase with time after injury in patients with projectile retention, and that the increase in significant part depended on the presence of a bone fracture caused by the gunshot.

CONCLUSION

We encountered evidence suggesting that the amount of blood lead increase in time after injury is also dependent on the tibia lead concentration. There were too few cases in the study to fully test the effects of bullet location, or the interaction of bullet location with bone fracture or bullet fragmentation.

Seasonal variation in bone lead contribution to blood lead during pregnancy

Population blood lead level (PbB) often shows seasonal variation, frequently being higher in summer and lower in winter. As vitamin D metabolites also show seasonal variability, and the metabolites are associated with bone metabolism, some authors have posited a role for bone lead release in seasonal PbB changes. We made third trimester and postdelivery PbB measurements on 414 immigrant women (98% Latina) in Los Angeles. We measured in vivo tibia and calcaneus (heel) lead concentration postdelivery via K-shell X-ray fluorescence. We saw evidence of seasonal variation in prenatal PbB, but not postnatal PbB. PbB was highest in spring and lowest in autumn. Tibia lead concentration was associated with prenatal PbB, as reported before. The contribution of tibia lead to prenatal PbB varied seasonally, with the greatest contribution occurring in the winter quarter and the least in the summer quarter. The temporal pattern of bone lead contribution to PbB follows the seasonal alteration of insolation. There was no seasonal component in prenatal PbB associated with calcaneus lead, nor were there seasonal variations in either calcaneus or tibia lead contributions to postnatal PbB. Bone turnover in the third trimester of pregnancy may be higher in winter months than in summer months, resulting in greater fetal lead exposure in spring than at other times of the year.

Maternal bone lead contribution to blood lead during and after pregnancy

We examined bone lead contribution to blood lead in a group of 311 immigrant women, 99% from Latin America, during the third trimester of pregnancy and 1 to 2 months after delivery. We measured in vivo tibia and calcaneus (heel) bone lead concentration in the postdelivery period with K shell X-ray fluorescence. Prenatal and postnatal geometric mean (range) blood lead level was 2.2 microg/dL (0.4 to 38.7) and 2.8 microg/dL (0.4 to 25.4), reflecting low current exposure. Postnatal blood lead level was significantly higher than prenatal (P<0.0001). Mean (range) tibia and calcaneus lead concentration was 6.7 microg/g (-33.7 to 62.2) and 8.4 microg/g (- 30.1 to 66.4), reflecting varying but elevated past lead exposure. Mean calcaneus lead concentration was significantly higher than mean tibia lead concentration (P = 0.055). Variance-weighted multiple regression and structural equation models showed that both calcaneus and tibia lead were directly associated with prenatal blood lead but only calcaneus lead was associated with postnatal blood lead. Increasing natural log years in the United States independently predicted decreasing calcaneus and third-trimester blood lead. The data suggest that while some exogenous lead sources and modulators of blood lead level, such as use of lead-glazed pottery and calcium in the diet, control lead exposure during and after pregnancy, endogenous lead sources from past exposure before immigration continue to influence blood lead levels in this sample.

Blood lead level and blood pressure during pregnancy in South Central Los Angeles

In many studies in which the relationship between blood pressure and blood lead level has been examined, investigators have found significant--but small--associations. There was only one previous report of a significant association of blood lead with blood pressure in pregnant women. We measured blood lead level and sitting blood pressure of 1,627 women in their third trimester of pregnancy. We eliminated subjects with known causes of hypertension. Most women (98.4%) were normotensive. We controlled for body mass index, age, and stress--among other factors--and constructed multiple-regression models of lead association with diastolic and systolic blood pressures. Immigrants (73% of total) had significantly higher blood lead levels and different blood pressures than nonimmigrants, suggesting that analysis be stratified by "immigrant, nonimmigrant" status. Positive relationships between blood lead level and blood pressure were found only for immigrants (p < or = .001). From the 5th to 95th blood-lead percentiles (0.9-6.2 microg/dl) in immigrants, systolic blood pressure increased 2.8 mm Hg, and diastolic blood pressure increased 2.4 mm Hg. Higher prior lead exposure of immigrants (97.7% from Latin countries) than nonimmigrants might explain the differential effect of these low levels of blood lead on blood pressure in nonimmigrants. Perhaps some immigrants are at higher risk than nonimmigrants for lead-associated elevated blood pressure during pregnancy, despite blood lead levels within the currently considered acceptable range.

Maternal blood lead level during pregnancy in South Central Los Angeles

Twenty-five years of public health efforts produced a striking reduction in lead exposure; the blood lead average in the United States has decreased to less than 20% of levels measured in the 1970s. However, poor minority groups that live in large urban centers are still at high risk for elevated lead levels. In this study, our data showed that pregnant immigrants (n = 1,428) who live in South Central Los Angeles--one of the most economically depressed regions of California--have significantly higher (p < .0001) blood lead levels (geometric mean = 2.3 microg/dl [0.11 micromol/l]) than 504 pregnant nonimmigrants (geometric mean = 1.9 microg/dl [0.09 micromol/l]). The most important factors associated with lower blood lead levels in both groups were younger age; more-recent date of blood sampling (i.e., decreasing secular trend); and blood sampling in mid-autumn, instead of mid-spring (i.e., seasonal trend). Blood lead levels of immigrants were strongly dependent on time elapsed since immigration to the United States; each natural log increase in years of residence was associated with an approximately 19% decrease in blood lead levels. Although blood lead means for both groups were almost the same as the estimated national average, 25 of the 30 cases of elevated blood lead (i.e., > or = 10 microg/dl [0.48 micromol/l) occurred in the immigrant group. The odds ratio (95% confidence intervals within parentheses) for having elevated blood lead levels (a) was 9.3 (1.9, 45.8) if the immigrant engaged in pica; (b) was 3.8 (1.4, 10.5) if the immigrant had low dietary calcium intake during pregnancy; and (c) was .65 (.43, .98) for every natural log unit increase of years of residence in the United States. The control of pica and dietary calcium intake may offer a means of reducing lead exposure in immigrants.

Blood lead levels in children in south central Los Angeles

We retrospectively reviewed 3 679 pediatric records from King/Drew Medical Center, south central Los Angeles, between 1991 and 1994. Blood lead levels of children were followed to age 18 y. Patients were not referred specifically for lead poisoning. The sample was primarily Latino. Geometric mean blood lead peaked at 6.7 micrograms/dl (0.32 mumol/l) between 2 and 3 y of age. There was a downward secular trend and a seasonal trend. Males had higher lead levels than females. Children who lived in several zipcode areas, in which the lowest family incomes were reported, had higher lead levels. More Latino children had higher lead levels than African American children. Latino children (i.e., 20.2%) who were 1-5 y of age had blood lead levels that were > or = 10 micrograms/dl. Young Latino children in this zone of Los Angeles may be at increased risk for lead exposure.