RESEARCH FOCUS 3-1 A GENETIC DIAGNOSIS

3-1 CELLS OF THE NERVOUS SYSTEM

RESEARCH FOCUS 3-2 BRAINBOW: RAINBOW NEURONS

NEURONS: THE BASIS OF INFORMATION PROCESSING

FIVE TYPES OF GLIAL CELLS

EXPERIMENT 3-1 QUESTION: CAN THE PRINCIPLES OF NEURAL EXCITATION AND INHIBITION CONTROL THE ACTIVITY OF A SIMPLE ROBOT?

CLINICAL FOCUS 3-3 BRAIN TUMORS

3-2 INTERNAL STRUCTURE OF A CELL

THE CELL AS A FACTORY

THE BASICS CHEMISTRY REVIEW

CELL MEMBRANE: BARRIER AND GATEKEEPER

THE NUCLEUS AND PROTEIN SYNTHESIS

THE ENDOPLASMIC RETICULUM AND PROTEIN MANUFACTURE

PROTEINS: THE CELL’S PRODUCT

GOLGI BODIES AND MICROTUBULES: PROTEIN PACKAGING AND SHIPMENT

CROSSING THE CELL MEMBRANE: CHANNELS, GATES, AND PUMPS

3-3 GENES, CELLS, AND BEHAVIOR

MENDELIAN GENETICS AND THE GENETIC CODE

APPLYING MENDEL’S PRINCIPLES

CLINICAL FOCUS 3-4 HUNTINGTON DISEASE

GENETIC ENGINEERING

PHENOTYPIC PLASTICITY AND THE EPIGENETIC CODE

A Genetic Diagnosis

Fraternal twins Alexis and Noah Beery seemingly acquired cerebral palsy perinatally (at or near birth). They had poor muscle tone and could barely walk or sit. Noah drooled and vomited, and Alexis had tremors.

Typically, children with cerebral palsy, a condition featuring perinatal brainstem damage, do not get worse with age, but the twins’ condition deteriorated. Their mother, Retta Beery, observed as well that Alexis’s symptoms fluctuated: they improved after she slept or napped, for example.

In searching the literature for similar cases, Retta found a photocopy of a 1991 news report that described a child first diagnosed with cerebral palsy, then found to have a rare condition, dopa-responsive dystonia. (Dystonia means abnormal muscle tone.) It stems from a deficiency of a neurochemical, dopamine, produced by a relatively small cluster of cells in the midbrain.

When Alexis and Noah received a daily dose of l-dopa, a chemical that some brain cells convert to dopamine, they displayed remarkable improvement. “We knew that we were witnessing a miracle,” Retta recalled.

A few years later, in 2005, Alexis began to have new symptoms marked by breathing difficulties. At this time the twins’ father, Joe, worked for Life Technologies, a biotech company that makes equipment used for sequencing DNA, the genetic coding molecule found in the nucleus of every cell. Joe arranged for samples of the twins’ blood to be sent to the Baylor College of Medicine’s DNA sequencing center.

The twins’ genome was sequenced and compared with that of their parents and close relatives. The analysis showed that the twins had an abnormality in a gene on chromosome 2 for an enzyme that enhances not only dopamine production but also the production of serotonin, another neurochemical made by brainstem cells (Bainbridge et al., 2011).

When the twins’ doctors added tryptophan, the enzyme that is converted to serotonin, to the l-dopa, both twins showed remarkable improvement. Alexis competed in junior high school track, and Noah played volleyball in the Junior Olympics. This is the first diagnosis established through genome sequencing that led to a treatment success, a scientific miracle indeed.