Tay-Sachs disease

Genetics, Metabolic Disorders No Responses »
Aug 122011
The most common of the lipid storage diseases, Tay-Sachs disease results from a congenital deficiency of the enzyme hexosaminidase A. It’s characterized by progressive mental and motor deterioration and is usually fatal before age 5, although some adolescents and adults with variations of hexosaminidase A deficiency have been noted.
Causes
Tay-Sachs disease (also known as GM2 gangliosidosis) is an autosomal recessive disorder in which the enzyme hexosaminidase A is virtually absent or deficient. This enzyme is necessary for metabolism of gangliosides, water-soluble glycolipids found primarily in central nervous system (CNS) tissues. Without hexosaminidase A, accumulating lipid pigments distend and progressively destroy and demyelinate CNS cells.
Tay-Sachs disease strikes persons of Eastern European Jewish (Ashkenazi) ancestry more often than the general population, occurring in about 1 in 2,500 live births in this ethnic group. About 1 in 25 Ashkenazi Jews are heterozygous carriers.
Signs and symptoms
A neonate with classic Tay-Sachs disease appears normal at birth, although he may have an exaggerated Moro reflex. By age 3 to 6 months, he becomes apathetic and responds only to loud sounds. His neck, trunk, arm, and leg muscles grow weaker, and soon he can’t sit up or lift his head. He has difficulty turning over, can’t grasp objects, and has progressive vision loss.
By age 18 months, the infant is usually deaf and blind and has seizures, generalized paralysis, and spasticity. His pupils are dilated and don’t react to light. Decerebrate rigidity and a vegetative state follow. The child suffers recurrent bronchopneumonia after age 2 and usually dies before age 5. A child who survives may develop ataxia and progressive motor retardation between ages 2 and 8.
The “juvenile” form of Tay-Sachs disease generally appears between ages 2 and 5 as a progressive Continue reading »
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Diagnosing autistic disorder

Genetics, Neurology No Responses »
Jul 212011
Autism is diagnosed when the patient meets the criteria in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition – Text Revision. At least six characteristics from the following three categories must be present, including at least two from the social interaction category and one each from the communication and patterns categories.
Social interaction
Patient displays impairment in social interaction, as shown by at least two of the following:
  • marked impairment in the use of multiple nonverbal behaviors, such as eye-to-eye gaze, facial expression, body postures, and gestures to regulate social interaction
  • failure to develop peer relationships appropriate to developmental level
  • no spontaneous sharing of enjoyment, interests, or achievements with others
  • lack of social or emotional reciprocity
  • gross impairment in ability to make peer friendships.
Communication
Patient displays impairment in communication, as shown by at least one of the following:
  • delay in or total lack of development of spoken language
  • in individuals with adequate speech, marked impairment in initiating or sustaining a conversation with others
  • stereotyped and repetitive use of language or idiosyncratic language
  • lack of varied, spontaneous make-believe play or social imitative play appropriate to developmental level.
Patterns
Patient displays restricted, repetitive, and stereotyped patterns of behavior, interests, and Continue reading »
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Approach to Genetic Disorders Presenting with Infantile Hypotonia

Genetics No Responses »
Feb 192011
Etiology
  • Hypotonia is a nonspecific sign that may be caused by a wide variety of etiologies.
  • Dysfunction in any component of the central or peripheral nervous system can cause hypotonia, including diseases of the muscle, neuromuscular junction, nerves, spinal cord, brain stem, cerebellum, basal ganglia, and cerebrum. Central hypotonia with peripheral spastic hypertonia is highly suggestive of central nervous system (CNS) involvement.
Clinical Presentation
  • Historical features supporting a genetic etiology include family history of neuromuscular disease, parental consanguinity, and a prior affected sibling. However, the absence of these features does not rule out a genetic cause.
  • Contractures in the newborn indicate prenatal onset but do not suggest a single, specific diagnosis.
  • Additional features that may indicate an underlying syndrome may not be present at a young age or may be difficult to appreciate in the neonate or infant.
Laboratory Studies
  • Several tests are recommended in the evaluation of a child with hypotonia and concern for a genetic disorder.
    • Blood tests: methylation studies for Prader-Willi and Angelman syndromes, creatine kinase, lactate and pyruvate, serum/plasma amino acids, comprehensive metabolic panel, karyotype (if normal, perform chromosomal microarray analysis), very long-chain fatty acids quantification, SMN molecular analysis (if reflexes absent), and Continue reading »
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