Oculopharyngeal Muscular Dystrophy

Excerpt

Clinical characteristics: Oculopharyngeal muscular dystrophy (OPMD) is characterized by ptosis and dysphagia due to selective involvement of the muscles of the eyelids and pharynx, respectively. For the vast majority of individuals with typical OPMD, the mean age of onset of ptosis is usually 48 years and of dysphagia 50 years; in 5%-10% of individuals with severe OPMD, onset of ptosis and dysphagia occur before age 45 years and is associated with lower limb girdle weakness starting around age 60 years. Swallowing difficulties, which determine prognosis, increase the risk for potentially life-threatening aspiration pneumonia and poor nutrition. Other manifestations as the disease progresses can include limitation of upward gaze, tongue atrophy and weakness, chewing difficulties, wet voice, facial muscle weakness, axial muscle weakness, and proximal limb girdle weakness predominantly in lower limbs. Some individuals with severe involvement will eventually need a wheelchair. Neuropsychological tests have shown altered scores in executive functions in some.

Diagnosis/testing: The diagnosis of OPMD is established in a proband with a suggestive phenotype in whom either of the following genetic findings are identified: a heterozygous GCN trinucleotide repeat expansion of 11 to 18 repeats in the first exon of PABPN1 (~90% of affected individuals) or biallelic GCN trinucleotide repeat expansions that are either compound heterozygous (GCN[11] with a second expanded allele) or homozygous (GCN[11]+[11], GCN[12]+[12], GCN[13]+[13], etc.) (~10% of affected individuals).

Management: Treatment of manifestations: Treatment for ptosis may include blepharoplasty by either resection of the levator palpebrea aponeurosis or frontal suspension of the eyelids. The initial treatment for dysphagia is dietary modification; surgical intervention for dysphagia should be considered when symptomatic dysphagia has a significant impact on quality of life. Physical and occupational therapy are encouraged; assistive devices may be necessary to prevent falls and assist with walking and mobility. Neuropsychological support as needed.

Surveillance: Routine evaluation of: neuromuscular and oculomotor involvement; dysphagia including nutritional status and diet; respiratory function given the increased risk for both aspiration and nocturnal hypoventilation; and cognitive function including development of psychiatric symptoms.

Genetic counseling: OPMD is inherited in an autosomal dominant manner. The risk to sibs of a proband depends on the genetic status of the parents of the proband:

1. If one parent of a proband is heterozygous for a GCN repeat expansion in PABPN1 (GCN[11_18]+ [10]) and the other parent has two normal alleles (GCN[10]+[10]), the risk to the sibs of inheriting a GCN repeat expansion is 50%.

2. If both parents of the proband are heterozygous for a GCN repeat expansion, sibs have a 25% risk of inheriting two GCN repeat expansions and a 50% risk of inheriting one GCN repeat expansion.

3. If one parent of the proband has biallelic GCN repeat expansions and the other parent has two normal alleles, all sibs will inherit a GCN repeat expansion.

4. If one parent of the proband has biallelic GCN repeat expansions and the other parent is heterozygous for a GCN repeat expansion, sibs of the proband have a 50% risk of inheriting biallelic GCN repeat expansions and 50% risk of inheriting one GCN repeat expansion.

Sibs who inherit either one or two GCN repeat expansions will be affected.