Although most neonates and infants with this disorder
appear to develop normally in the first few months of life, the presence of
poor muscle tone most often already is present at birth. By age 6 months,
hypotonia, inability to hold up the head, and severe muscle atrophy are
detectable. Severe mental retardation is associated with multiple congenital
Allan-Herndon-Dudley Syndrome; AHDS; X-Linked Mental
Retardation with Hypotonia.
X-linked recessive. Gene located in Xq21.
Based on clinical features and family history.
Only males are affected. Except for hypotonia,
these boys appear normal at birth. When the child is approximately 6 months
old, the parents often notice that the child is unable to hold up the head.
Motor development is severely impaired so that the ability to walk is
achieved either very late or not at all. Generalized muscular atrophy, which
is associated with myopathic findings on histologic examination, becomes
obvious in early infancy. Later in infancy, spastic paraplegia with joint
contractures, hyperreflexia with clonus, ataxia, athetosis, and dysarthria
become increasingly more obvious. Scoliosis may occur. Mental retardation
usually is severe. Craniofacial anomalies may include elongation and
bitemporal narrowing of the head with enlarged and dysplastic ears. Pectus
excavatum has been described in many of these boys.
Assess the degree of scoliosis,
pectus excavatum, and joint contractures. If scoliosis or pectus excavatum
is severe, assess pulmonary function and obtain a chest radiograph, arterial
blood gas analysis, and pulmonary function tests if possible.
Echocardiography may be indicated if there are any concerns about heart
function (cor pulmonale).
The presence of severe mental
retardation suggests a lack of cooperation, and sedation in the older child
prior to induction of anesthesia may be required. Careful positioning and
padding are required because of contractures. Depending on the degree of
scoliosis and pectus excavatum, postoperative mechanical ventilation may be
required. As in any patient with signs of muscular hypotonia and/or
myopathy, depolarizing muscle relaxants should be used only with caution.
Whether these patients have a predisposition to malignant hyperthermia is
unknown, but it may be wise to provide a trigger-free anesthesia.
None reported; however, an
exaggerated hyperkalemic response to succinylcholine should be expected. No
data on the predisposition to malignant hyperthermia are available, so use
of succinylcholine probably is best reserved for special situations.
Fragile X Syndrome: The most common form of X-linked mental
retardation (XLMR). Affects males more often and more severely than females.
Only subtle dysmorphic features. Behavioral issues may be more pronounced.
Juberg-Marsidi Syndrome: X-linked recessive inherited syndrome
characterized by severe mental retardation, deafness, failure to thrive,
microgenitalism, and early death.
Happy Puppet Syndrome: Rare disorder characterized by
developmental delay, ataxia, dysmorphic facial features, and seizures
associated with a happy, sociable disposition.
MASA Syndrome: Extremely rare inherited disorder that is one
of several disorders known ...