LESCH-NYHAN
SYNDROME (LNS) |
ALTERNATE NAMES
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Hereditary Hyperuricemia and Choreoathetosis Syndrome; Hyperuricemia Choreoathetosis-Self
mutilation Syndrome; Hyperuricemia-Oligophrenia; Hypoxanthine-Guanine Phosphoribosyltranferase
Deficiency (HGPRT); Hypoxanthine phosphoribosyltransferase Deficiency (HPRT); Juvenile
Gout-Choreoathetosis and Intellectual Disability Syndrome; Lesch Nyhan Disease; Nylan
Syndrome
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DESCRIPTION
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Lesch-Nyhan syndrome (LNS) is a rare, inherited disorder caused by a deficiency of the enzyme hypoxanthine-guanine
phosphoribosyltransferase (HPRT). LNS is an X-linked recessive disease-- the gene
is carried by the female parent and passed on to male children. The lack of HPRT causes
a build-up of uric acid in all body fluids, and leads to severe gout, poor muscle
control, and moderate intellectual disability, which appear in the first year of life.
Hypotonia and delayed motor milestones are usually evident by three to six months
of age. The motor disability is so severe that virtually all children with LNS never
walk and will need a wheelchair or mobility device. Neurological signs include facial
grimacing, involuntary writhing, and repetitive movements of the arms and legs similar
to those seen in Huntington's disease. A striking feature of LNS is self-mutilating
behaviors - characterized by lip and finger biting - that begin in the second year
of life. Because a lack of HPRT causes the body to poorly utilize vitamin B12, some
males may develop a rare disorder called megaloblastic anemia.
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DIAGNOSTIC TESTING, PHYSICAL FINDINGS, AND
ICD-9-CM/ICD-10-CM
CODING
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Diagnostic testing: Molecular genetic testing is the most effective method of testing, as HPRT1 is the
only gene known to be associated with LNS. Children who display the full Lesch-Nyhan
phenotype all have mutations in the HPRT1 gene. Some consider the definitive confirmatory
test to be the results of HPRT enzyme activity of less than 1.5% of normal blood or
other type tissue cells.
Physical findings: Physical findings for LNS may include:
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Psychomotor delay with a delay in head support and sitting;
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Hypotonia (decreased muscle tone);
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Athetoid (slow, involuntary, writhing movement of fingers, hands, toes, and feet)
movements;
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Sandy urine or crystalluria (cloudy urine caused by crystals) with urinary tract obstruction
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Severe action dystonia (involuntary muscle contractions) with baseline hypotonia that
may lead to an inability to stand up and walk;
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Involuntary movements (choreoathetosis and ballismus) associated with voluntary movements
increased by stress but not evident at rest;
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Dysarthria (slurred or slow speech);
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Dysphagia (difficulty swallowing);
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Opisthotonus (nuscle spasms causing backward arching of the head, neck, and spine);
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Hyperreflexia (overactive or overresponsive reflexes) and extensor plantar reflex
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Mild to moderate intellectual deficit;
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Obsessive-compulsive self-mutilation (lip biting or finger chewing);
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Aggressive behavior (i.e. spitting, abusive language);
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Urolithiasis (kidney stones); and
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Renal failure or acidosis occur rarely.
ICD-9: 277.2
ICD-10: E79.1
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PROGRESSION
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The prognosis for children with LNS is poor. Death usually occurs in the first or
second decade of life.
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TREATMENT
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Treatment for LNS is symptomatic. Gout can be treated with allopurinol to control
excessive amounts of uric acid. Kidney stones may be treated with lithotripsy, a technique
for breaking up kidney stones using shock waves or laser beams. There is no standard
treatment for the neurological symptoms of LNS. Some may be relieved with the drugs
carbidopa/levodopa, diazepam, phenobarbital, or haloperidol.
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SUGGESTED
PROGRAMMATIC ASSESSMENT* |
Suggested MER
for Evaluation: LNS is diagnosed by HPRT enzyme activity less than 1.5% of normal in tissue cells
or genetic test results showing mutation in the HPRT1 gene and clinical description
of the physical and developmental findings consistent with LNS.
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Suggested
Listings for Evaluation: |
DETERMINATION
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LISTING
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REMARKS
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Meets |
110.08 |
Laboratory confirmed diagnosis of LNS that interferes very seriously with development. |
111.17
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Equals |
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* Adjudicators may, at their discretion, use the Medical Evidence of Record or the
listings suggested to evaluate the claim. However, the decision to allow or deny the
claim rests with the adjudicator.
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