Genetic Analysis of Brain Disorders

Holoprosencephaly (HPE) covers a nearly continuous spectrum of midline abnormalities ranging
from unmistakable cyclopia with absence of forebrain separation to mild microforms, such a
single central incisor. Inder this research protocol, we deliberately keep the inclusion
criteria as inclusive as possible to encompass the entire range of severity of the disorder.

The objective of these studies is to identify genetic factors that contribute to the
pathogenesis of holoprosencephaly (HPE) or related brain malformations. Our approach
involves the analysis of chromosomal rearrangements, use of positional cloning and gene
isolation, and mutational analysis of candidate genes. All individuals with overt or subtle
clinical findings consistent with the HPE spectrum are eligible to participate. Mutational
analysis of our entire coded collection of HPE probands (approximately 600 cases) in
selected genes is the principal research method used to determine that a given candidate
gene is commonly mutated in HPE. We continuously re-evaluate the available mutational
analysis methods in an effort to stay current with high-throughput technologies. Currently,
we use denaturing high performance chromatography for initial mutation screens combined with
sequencing. In the coming year(s) we may evaluate new technologies, such as high-resolution
melting procedures, comparative genomic sequencing. Whenever a sequence variant is
identified, that is not present in a commercially available control set of samples, attempts
are made to test the functional significance of this change on the protein itself, or its
expression. Sequence changes with a strong probability of being medically significant will
be verified in a CLIA-approved lab (e.g. Muneke lab, for selected genes, or Gene Dx) at our
expense, before any results are given to the family through genetic counseling. Parental DNA
(and rarely that of siblings) is usually obtained at the same time that a proband is
enrolled. Typically, these samples are studied only to perform limited family studies once a
sequence variant of potential medical significance has already been determined. Linkage
studies under this protocol are anticipated to be rare (ad hoc) studies and will proceed
only following an independent evaluation that there is sufficient statistical power and
strong likelihood of success. This research is best evaluated by our progress in the
identification of genetic factors that contribute to normal and abnormal brain development.

The majority of subjects enrolled in this study will continue under the care of their local
physician or genetic counselor with limited contact with the NIH investigators. Only rarely
will families be seen at the NIH CC. These visits will involve face to face genetic
counseling of medically significant results, following verification in a CLIA approved lab.
This is not a treatment protocol. Our empiric ability to generate medically significant
research results is limited by the extensive genetic and other etiologic heterogeneity.
Therefore, for most participants this research is not a diagnostic study.

We have modified our procedures to test all new probands for mutations in the four HPE genes
(SHH, ZIC2, SIX3 and TGIF) that are the best documented genes associated with HPE. Our lab
is now certified to receive and test new samples according to CLIA guidelines. However, all
previously collected samples will not be considered suitable for diagnostic purposes; hence,
a second sample will need to be requested in these cases for CLIA confirmation.

- INCLUSION CRITERIA:

1. This research is open to all participants with a known or suspected diagnosis of
HPE or related brain malformations. Since the range of severity of HPE is
extensive, we accept cases compatible with a wide HPE spectrum of findings. All
races and genders are known to be at risk for HPE, anywhere in the world.
Nationality or place of origin are not specific barriers to participation,
provided that a blood tissue sample can be safely sent by international FedEx
(to be billed to our account).

2. Direct blood relatives (typically parents, and occasionally siblings of affected
individuals) of patients with HPE are also eligible to participate.

EXCLUSION CRITERIA:

1. Anyone unwilling to provide informed consent (for themselves as adults, or on behalf
of their children as minors) or assent.

2. Medical condition(s) or mental retardation are not in themselves reason for exclusion
if in the judgement of the referring physician this would involve no more than
minimal risk. We anticipate that children with mental handicaps would be included in
the research population. We will make every effort to explain the study for the
purpose of assent in a matter that the family feels is both age and developmentally
appropriate for that child.

3. We generally review a brief clinical description from the referring physician about a
potential research subject to determine that the subject is appropriate to enter into
the study. We reserve the right to exclude cases that are clearly not HPE or related
to our direct research interests (e.g. HPE cases due to Trisomy 13 or 18 might not be
considered directly related to current research). This almost never happens, and we
would attempt to make referrals to a more appropriate investigator before a sample is
sent to the NIH. Although not desirable, we will accept samples with a suspected
diagnosis of HPE where this determination was made by the referring physician
independent of any input from our HPE team. In such circumstances, we would likely
verify by correspondence that a sample had been received and request further
information.