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Chromosome 22 Central Inc.
is a registered Canadian Non-Profit Organization
and Registered Charity BN# 86009 3665 RR0001, and a Registered US
Corporation with Non-Profit Status
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CHROMOSOME
BASICS....
UNDERSTANDING EMANUEL SYNDROME
To begin with, a bit of
background: every cell in our bodies contains a complete set of plans for
carrying out every function that every kind of cell will need. These plans
are hereditary material, and are found in each cell, in 23 pairs of
chromosomes. The complete set of plans is named the genome. In the human
genome, there is approximately 50,000-100,000 genes. One exception that
every cell contains 23 pairs of chromosomes is the reproductive cells, the
egg from the mother, and the sperm from the father. Each contain only half
of the normal number required, for when the sperm and egg unite, a new
cell will be created with the proper amount of genetic material for a new
person. Each parent provides half of the genetic material for a new baby.
The abbreviated chemical
name for the material that creates genes is called DNA, which stands for
deoxyribonucleic acid. A chromosome is basically a very long strand of
DNA.
Chromosomes can be studied
microscopically by chemically staining them. This process is called the
karyotype. The cells are obtained by taking a blood sample from a person.
The stained chromosomes show a pattern of light and dark band. Each
chromosome pair has a usual length, and characteristic markings, and each
set is assigned numbers, with #1 being the longest chromosome, and 22
being one of the shorter ones. Each chromosome also has a specific
"bend" along it at some point, which is called the centromere .
The longer part of the chromosome is called the long arm, or the
"q" and the short arm is called the "p" for
"petite).
In the case of unbalanced
translocation 11;22, the occurrence usually arises when one of the parents
is a carrier of a balanced translocation. This means, that the information
from a specific breakpoint on each of the long arms of chromosomes 22 and
11, have switched places. The balanced carrier is normal, because all of
the genetic information is still all there in the right proportions, even
though it is not is it's usual place. When an unbalanced embryo is
conceived, the material it contains is 2 proper #11 chromosomes, 2 proper
#22 chromosomes, and one extra chromosome which contains material from
both the 11 & 22 chromosomes. It receives this from the carrier
parent. Click here for a
graphic explanation.
A past study done by Dr.'s
Emanuel and Zackai discussed the risks of recurrence for carriers. In the
families they studied, the risk of a female carrier having a malformed
newborn was calculated to be 4.3%, or possibly as high as 10%, as three
cases that were malformed, and not karyotyped, were excluded from the
figures. The figure for the male would be slightly lower. The chance of a
female carrier having a child that would also be a balanced carrier, is
68%, and for the male carriers, the chance of having a balanced carrier
child would be 77.8%. For the rate of miscarriage, the female carriers
risk is 30.3%, and the spouses of the male carriers would be 48.1%. The
average is 35.5% for a spontaneous abortion. The total calculated risk for
any abnormal pregnancy outcome, is 37.1% for female carriers, 51.9% for
male carriers, and the combined total being 41.2%. This figure includes
both spontaneous abortions and unbalanced carrier children.
REFERENCES:
Zackai EH, Emanuel BS:
Site-specific reciprocal translocation, t(11;22)(q23;q11), in several
unrelated families with 3:1 meiotic disjunction. Am J Med Genet 1980.
Iselius L, et al: The
11q;22q translocation: a collaborative study of 20 new cases and analysis
of 110 families.
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HEAD OFFICE - for ALL inquiries:
Chromosome 22 Central, c/o Stephanie St-Pierre, 237 Kent Avenue, Timmins,
Ontario, Canada P4N 3C2 tel/fax: (705) 268-3099, EMAIL: steph.stpierre@gmail.com
US Head Office - for US donations: Chromosome 22 Central, c/o Murney
Rinholm, 7108 Partinwood Drive, Fuquay-Varina, North Carolina, 27526
USA, tel (919) 567-8167, EMAIL: bgr@nc.rr.com
Latin America / Spanish inquiries -
Laura Munoz, Robinson Crusoe 1209, Las
Condes - Santiago, Chile tel: 02-3251262 EMAIL: lauramuno@hotmail.com
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