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Alobar Holoprosencephaly
Holoprosencephaly is a complex intracranial abnormality characterized by absent or incomplete cleavage of the Prosencephalon (1).From a genetic point of view all holoprosencephalies have the same significance. Their frequency is estimated at 1 in 16,000 to 1 in 18,000 births (2).Holoprosencephalies have a heterogenous cause; chromosomal aberration is found in about one half of the cases. Chromosome 13 is most frequently involved. Partial deletion of chromosome 13 as well as trisomy may coexist with Holoprosencephalies. (2) Holoprosencephaly as, an autosomal dominant inheritance is rare but certainly exists. Recurrence risk after an isolated case of holoprosencephaly with normal chromosome is 5-6% (3).During the fourth gestational week, the neural tube forms three primary brain vesicles: the prosencephalon, mesencephalon and rhombencephalon. During the fifth week the forebrain (Prosencephalon) further divides into secondary vesicles: the telencephalon and diencephalons. Partial division of the telencephalon into two cerebral hemisphere occurs by the end of the fifth fetal week. Complete or partial failure in division of the developing cerebrum (Prosencephalon) into hemispheres and lobes results in the Holoprosencephalies. (4)Alobar form is rare malformation consisting of large Holospheric Brain. Alobar holoprosencephaly is characterized by nearly complete lack of ventricular and hemispheric cleavage. The Brain is basically an undifferentiated Holosphere with central monoventricle and fused thalami (4). 17% cases of Holoprosencephaly are reported with no facial anomaly (5).

Reference
Macahan PJ, Nyberg AD, Mack AL. Sonography of facial feature of alobar and semi lobar Holoprosencephaly. AJR, 1990:154:143-148.
Barness EG.Prosencephalon Growth Failures. Potter's Pathology of the Foetus And Infants.3rd Ed: Vol 2:Mosby: 1997:1056-1059.
Baraister M, Winter RM. Holoprosencephaly.Color atlas of Congenital Malformation Syndrome.Mosby: 1996:148.
Osborn AG. Disorders of Diverticulation and Cleavage, Sulcation and Cellular Migration. Diagnostic Neuroradiology.1st Ed: Vol 1:Mosby, 1994:37-39.
Dahnert WG, Radiology Review Manual. 3rd Ed: Williams &Wilkins, 1996:213-214.

Ind J Radiol Imag 2003 13:3:295-296
Reviewed by Sumer Sethi on Sunday, October 10, 2004 Rating: 5

2 comments:

nobody said...

im doing a presentation on holoprosencephaly in general and was wondering if you could explain the mechanisms underlying this condition? or give any helpful links? would be much appreciated, weeks of looking through pubmed have been unsuccesful.. in particular, how exactly are mutations in shh thought to lead to this? midline specification?

thanks..

kdnaquin said...

I came accross your site while searching for information on HPE. I am from the United States. I lost a child 9 years ago with Alobar HPE and her chromosomes were normal. We were told our risk of having another was greater. We had another child a year later and almost lost her at two weeks of age to RSV. Every test possible was done on her and everything came up normal. She is now 7 years old and is cognatively and mentally delayed by at least 4 years. We never had another child from the fear of having to deal with possibly lossing another child again or having to worry about the development of another child surviving. I am still searching for the understanding of this disorder and I guess I am still just wanting to know why...I do not get too many responses about it because my child did not survive in other words is not still living like some children. This condition is very close to my heart. Thank you for your post on HPE... I guess finally there are more people getting involved with trying to understand this rare condition.

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