Second edition

09.qxd 3/10/08 9:39 AM Page 422
422 Congenital, developmental, and other childhood-onset disorders
is different from that on the page. The errors in reading often
involve omitting certain letters or supplying a different letter
than the one printed; letter reversals often occur, such as ‘d’
for ‘b’. In some cases, entire words are reversed, with the
child saying ‘pat’ for the written word ‘tap’, for example.
Reading comprehension is impaired and, after finally, and
haltingly, reading a paragraph, the child may be unable to
paraphrase it in his or her own words. In striking contrast, if
the same paragraph is read out loud to the child, he or she
may then be able to paraphrase it with little difficulty.
Writing is also impaired, and similar reversals may be
seen. Thus, intending to write ‘top’, the child may write
‘pot’. In some cases entire sentences may be reversed, with
the written words reading from right to left on the page. Of
note, if the child is asked to take a look at what he or she
has written and then asked if there are any errors, the
answer is often ‘no’.
Course
Although there may be some spontaneous improvement
over long periods of time, the overall natural course is
marked by a chronic difficulty in reading.
Etiology
Developmental dyslexia is clearly familial; concordance
among dizygotic twins is about 25 percent, and among
monozygotic twins it rises to about 50 percent. Genetic heterogeneity
exists (Williams and O’Donovan 2006), with loci
identified on chromosomes 1, 3, 6, and 7. Autopsy studies in
males reveal cortical dysgenesis, which, although widespread,
is concentrated in the left peri-sylvian areas (Galaburda et al.
1985). In females, although similar findings were noted,
there was, in addition, widespread glial scarring (Humphreys
et al. 1990). Of note, and again in males, dysplastic changes
have also been identified in the medial geniculate body and
the posterior lateral nucleus of the thalamus (Galaburda and
Eidelberg 1982). Magnetic resonance scanning has also suggested
a lack of normal cerebral asymmetry of the planum
temporale (Hynd et al. 1990); however, not all studies agree
on this (Rumsey et al. 1997). Of interest, recent work has
demonstrated that specific evoked potential abnormalities in
infants predict the appearance of dyslexia (Molfese 2000).
Overall, it appears likely that developmental dyslexia
occurs secondary to an inherited disturbance of neuronal
migration, resulting in cortical microdysgenesis of the
temporal cortex.
Differential diagnosis
Decreased visual acuity, severe anxiety, or a less than adequate
educational setting may all impair a child’s ability to
learn to read.
Mental retardation is characterized by deficient reading,
but here, in contrast to developmental dyslexia, one finds
deficits in other academic skills.
Treatment
Remedial education is often strikingly effective. Piracetam,
not available in the United States, may be helpful (Wilsher
et al. 1987); however, not all studies agree on this (Ackerman
et al. 1991).
9.18 DEVELOPMENTAL DYSGRAPHIA
Developmental dysgraphia (Deuel 1995; Gubbay and de
Klerk 1995; Roeltgen and Tucker 1988), also known as
developmental agraphia or ‘disorder of written expression’,
is characterized by an impaired acquisition of the
ability to write, despite normal intelligence and adequate
educational opportunity. This is probably an uncommon
disorder, and is probably more common in boys than girls.
Clinical features
Children with this disorder often misspell words; their sentences
tend to be short and deficient in terms of grammar
and syntax, and at times whole words may be missing,
giving sentences a ‘telegraphic’ quality. Penmanship may
or may not be poor; at times the penmanship far outshines
what is actually written. Importantly, and in stark contrast
to what they write, these children are often able to express
themselves quite well when speaking.
Course
In the natural course of events, developmental dysgraphia
appears to be chronic.
Etiology
Apart from the fact that dysgraphia tends to run in families
(Schulte-Korne 2001), little is known about its etiology.
Differential diagnosis
Developmental dyslexia is distinguished by a concurrent
difficulty with reading, and mental retardation by associated
deficits in other academic abilities.
Treatment
Remedial education is effective.