Menkes disease and occipital horn syndrome (OHS) are X-linked disorders of copper transport caused by mutations in the copper-transporting ATPase (ATP7A) gene. These disorders result in low concentrations of copper in some tissues due to impaired intestinal copper absorption, accumulation of copper in other tissues, and reduced activity of copper-dependent enzymes such as dopamine beta hydroxylase (DBH) and lysyl oxidase.
Infants with classic Menkes disease appear healthy until age two to three months when growth retardation, hypotonia, and seizures occur. Other manifestations include peculiar hair (short, sparse, coarse, twisted, often lightly pigmented) and focal cerebral and cerebellar degeneration. Temperature instability and hypoglycemia may be present in the neonatal period. Death usually occurs by three years of age.
Occipital horn syndrome is characterized by "occipital horns," which are distinctive wedge-shaped calcifications at the sites of attachment of the trapezius muscle and the sternocleidomastoid muscle to the occipital bone. Occipital horns may be clinically palpable or observed on skull radiographs. Individuals with OHS also have lax skin and joints, bladder diverticula, inguinal hernias, and vascular tortuosity. Intellect is normal or slightly reduced.
The ATP7A (Xq12-q13) gene encodes copper-transporting ATPase 1, which transports copper across cellular membranes and is critical for copper homeostasis. ATP7A mutations may result in a gene product with no copper transport capability (associated with a severe phenotype) or a reduced quantity of normally functioning gene product (associated with a milder phenotype). Phenotypic variability is observed in families with mild mutations, but not in those with severe mutations. In affected individuals, approximately 80% of known mutations are point mutations, while approximately 15% are deletions. Approximately one-third of males have de novo mutations. The incidence of Menkes disease and its variants is estimated at 1/100,000 births.
For patients with suspected Menkes disease or OHS, sequence analysis is recommended as the first step in mutation identification. For patients in whom mutations are not identified by full gene sequencing, deletion/duplication analysis is appropriate.
Due to the presence of a pseudogene for the ATP7A gene, analysis of deletion or duplication of exon 11 cannot be included in this assay.
Please click here for the GeneReviews summary on this condition.
This test is indicated for:
- Confirmation of a clinical/biochemical diagnosis of Menkes disease or OHS in an individual in whom sequencing analysis was negative.
- Carrier testing in adult females with a family history of Menkes disease or OHS in whom sequencing analysis was negative.
DNA isolated from peripheral blood is hybridized to a CGH array to detect deletions and duplications. The targeted CGH array has overlapping probes which cover the entire genomic region.
Detection is limited to duplications and deletions. The CGH array will not detect point or intronic mutations.
Results of molecular analysis must be interpreted in the context of the patient's clinical and/or biochemical phenotype.
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
- Menkes Disease: ATP7A Gene Sequencing (RZ) is required before deletion/duplication analysis.
- X-Linked Mental Retardation: 64-Genes Deletion/Duplication Comprehensive Panel (OL).
- Prenatal testing is available to couples who are confirmed carriers of mutations. Please contact the laboratory genetic counselor to discuss appropriate testing prior to collecting a prenatal specimen.