Archive | July 2011

Zellweger syndrome or cerebrohepatorenal syndrome

Zellweger syndrome, also called cerebrohepatorenal syndrome is a rare, congenital disorder (present at birth), characterized by the reduction or absence of peroxisomes in the cells of the liver, kidneys, and brain. It is one of a family of disorders called leukodystrophies.

Zellweger syndrome is an autosomal recessive disorder caused by mutations in genes that encode peroxins, proteins required for the normal assembly of peroxisomes.

As a result of impaired peroxisome function, an individual’s tissues and cells can accumulate very long chain fatty acids (VLCFA) and branched chain fatty acids (BCFA) that are normally degraded in peroxisomes. The accumulation of these lipids can impair the normal function of multiple organ systems, as discussed below. In addition, these individuals can show deficient levels of plasmalogens, ether-phospholipids that are especially important for brain and lung function

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Cri du chat Syndrome, chromosome 5p deletion syndrome, 5p minus syndrome or Lejeune’s syndrome

Cri du chat syndrome is a group of symptoms that result from deletion on chromosome number 5. The syndrome’s name is based on the infant’s cry, which is high-pitched and sounds like a cat.

It was first described by Jérôme Lejeune in 1963.

Approximately 90% of cases results from a sporadic, or randomly-occurring, de novo deletion. The remaining 10-15% are due to unequal segregation of a parental balanced translocation where the 5p monosomy is often accompanied by a trisomic portion of the genome. These individuals may have more severe disease than those with isolated monosomy of 5p.

Loss of a small region in band 5p15.2 (cri du chat critical region) correlates with all the clinical features of the syndrome with the exception of the catlike cry, which maps to band 5p15.3 (catlike critical region). The results suggest that 2 noncontiguous critical regions contain genes involved in this condition’s etiology. Two genes in these regions, Semaphorine F (SEMA5A) and delta catenin (CTNND2), are potentially involved in cerebral development. The deletion of the telomerase reverse transcriptase (hTERT) gene localized in 5p15.33 may contribute to the phenotypic changes in cri du chat syndrome as well.

Symptoms

Signs

In addition to symptoms, the physical examination may show:

Diagnositics:

Genetic tests show the deletion on chromosome 5.

Skull x-ray may reveal an abnormal angle to the base of the skull.

Source: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002560/

Karyotype

Male Karyotype: 46 XY

There is a specific way to label a karyotype.  A human has 23 sets of chromosomes, and thus, a total of 46 chromosomes.  Twenty-two of these pairs are autosomal chromosomes, and the last pair is comprised of the sex chromosomes, which don’t have to be identical.  A karyotype is labeled in the following fashion:   number of chromosomes, sex chromosomes (by listing XX for female, or XY for male), any genetic malfunctions.  For example, a normal male would be 46, XY, and a normal female would be 46, XX.

Labelling the chromosome using international cytogenetic nomenclature

inversion and transloation examples shown below by arrows

Source: http://dwb4.unl.edu/Chem/CHEM869N/CHEM869NLinks/library.thinkquest.org/18258/noframes/ped-karyo2.htm

Carpenters syndrome

Carpenter syndrome, also called acrocephalopolysyndactyly type II, is an extremely rare autosomal recessive congenital disorder characterized by craniofacial malformations, obesity, and syndactyly.

Apert Syndrome

Apert syndrome is a form of acrocephalosyndactyly, a congenital disorder characterized by malformations of the skull, face, hands and feet. It is classified as a branchial arch syndrome, affecting the first branchial (or pharyngeal) arch, the precursor of the maxilla and mandible

Genetic Counselling: An introduction

Genetic counselling: The process by which patients or relatives at risk for a disorder that may be hereditary are advised of

  1. The consequences of the disorder
  2. The probability of developing or transmitting the disorder
  3. The ways in which this may be prevented, avoided or ameliorated

It involves elements from several disciplines:

  • psychotherapy – supportive counselling of a social field
  • diagnositics – clincial medincal testing of the inherited disease
  • mathematics – complex mathematical, statictical process involving the estimationo risk

The core elements of genetic counselling practice

  • Diagnostic and clinical aspects
  • Documentation of family and pedigree information
  • Recognition of ineritance patterns and risk estimation
  • Communication and empathy with those seen
  • Infomation on available options and further measures
  • Support in decision-making and for decisions made

Considerations when interviewing:

  1. Did the family themselves initiate the request for genetic counselling or did someone else?
  2. Is there an unspoken or an exaggerated fear of the disorder?
  3. Do feelings of guilt or hostility exist between parents?
  4. Is the rest of the family supportive or are there tensions between the generations?
  5. Is an affected child valued, loved, or regarded as a burden?

Note: The answers to most of these questions may be obtained by an astute clincian without the need for direcr questioning.

Symbols used in drawing of a pedigree

Nuchal cord

A nuchal cord occurs when the umbilical cord becomes wrapped around the fetal neck 360 degrees.

There are two types:

  • “Type A” nuchal cord is wrapped around the neck 360 degrees.
  • “Type B” pattern is described as a hitch which cannot be undone and ends up as a true knot
Management:
Goal: To protect umbilical circulation whenever possible. Techniques to preserve an intact nuchal cord depend on how tightly the cord is wrapped around the infant’s neck.
  1. If the cord is loose, it can easily be slipped over the infant’s head. The infant can be delivered normally and placed on maternal abdomen as desired.
  2. If the cord is too tight to go over the infant’s head, the provider may be able to slip it over the infant’s shoulders and deliver the body through the cord. The cord can then be unwrapped from around the baby after birth.
  3. If the cord is too tight to slip back over the shoulders, one may use the somersault maneuver to allow the body to be delivered.
  • The birth attendant may also choose to clamp and cut the umbilical cord to allow for vaginal delivery if other methods of nuchal cord management are not feasible.
Prognosis:
“Coils occur in about 25% of cases and ordinarily do no harm, but occasionally they may be so tight that constriction of the umbilical vessels and consequent hypoxia result.” Williams Obstetrics 16th Edition