Hyperphagia, severe obesity, impaired cognitive function, and hyperactivity associated with functional loss of one copy of the brain-derived neurotrophic factor (BDNF) gene

Abstract

The neurotrophin brain-derived neurotrophic factor (BDNF) inhibits food intake, and rodent models of BDNF disruption all exhibit increased food intake and obesity, as well as hyperactivity. We report an 8-year-old girl with hyperphagia and severe obesity, impaired cognitive function, and hyperactivity who harbored a de novo chromosomal inversion, 46,XX,inv(11)(p13p15.3), a region encompassing the BDNF gene. We have identified the proximal inversion breakpoint that lies 850 kb telomeric of the 5' end of the BDNF gene. The patient's genomic DNA was heterozygous for a common coding polymorphism in BDNF, but monoallelic expression was seen in peripheral lymphocytes. Serum concentration of BDNF protein was reduced compared with age- and BMI-matched subjects. Haploinsufficiency for BDNF was associated with increased ad libitum food intake, severe early-onset obesity, hyperactivity, and cognitive impairment. These findings provide direct evidence for the role of the neurotrophin BDNF in human energy homeostasis, as well as in cognitive function, memory, and behavior.

FIG. 1

Mapping of a de novo chromosome 11 paracentric inversion in an 8-year-old girl with severe obesity and developmental delay. A: G-banding of the patient’s metaphase chromosomes revealed a paracentric inversion extending 11p13 to 11p15.3. B: FISH mapping of the breakpoint-spanning BAC, RP11-1061A15 (red), and a midinversion BAC, RP11–580I19 (green). In the normal chromosome 11 (nl 11), RP11-580I19 (green) lies ~8-Mb distal to RP11-1061A15 (red). In the abnormal chromosome (inv 11), red signal from RP11-1061A15 is seen both proximal and distal to the midinversion BAC (green). BAC clones were obtained from BACPAC Resources Center (http://bacpac.chori.org/home.htm). C: Schematic map of the proximal breakpoint region, showing relative positions of BACs used for FISH analysis, the BDNF gene, and mapping of the region that was subsequently analyzed using Southern hybridizations. BACs (1-Mb apart) were initially used to identify the approximate region of the breakpoint. Further FISH analysis using overlapping BACs saturating the identified region allowed for further mapping of the breakpoint to an ~40-kb region, as shown. Subsequent Southern hybridization analysis used known BAC sequence (RP11–22P3, AC015518) to design probes against HindIII fragments across this ~40-kb proximal breakpoint region. Patient and control genomic DNA was digested with HindIII and incubated with the PCR-derived P32-labeled probes. The probe, as indicated on the schematic, revealed an aberrant ~5.5-kb junction fragment in the patient (inset).

FIG. 2

Monoallelic expression and low serum BDNF concentrations in the proband. A: Genomic and cDNA sequences from the patient’s lymphoblastoid cell line. The patient is heterozygous for the BDNF coding polymorphism, Val66Met. However, her cDNA sequence reveals RNA expression of the 66Met allele only, indicating monoallelic expression of BDNF in this patient. B: BDNF serum protein levels were measured after an overnight fast using a commercially available enzyme-linked immunosorbent assay. Serum BDNF in the patient was compared with that in age-matched normal-weight control subjects and age-matched obese girls and boys (>95th percentile; mean BMI SDs 2.3 for boys, 2.6 for girls).

FIG. 3

Obesity phenotype of an 8-year-old girl with haploinsufficiency at the BDNF locus. A: Weight gain compared with normal U.K. percentiles for girls. B: Food intake at an 18-MJ ad libitum test meal, expressed per kilogram lean body mass, compared with subjects with mutations in other genes responsible for obesity syndromes and controls. Food intake is expressed per kilogram lean body mass measured by dual-energy X-ray absorptiometry to allow comparison between subjects of different ages. C: Measured basal metabolic rate measured by indirect calorimetry compared with predicted values. The BDNF-haploinsufficient patient is highlighted and compared with age- and BMI-matched obese control subjects.