Mecp2 Disorders

Clinical characteristics.

The spectrum of MECP2-related phenotypes in females ranges from classic Rett syndrome to variant Rett syndrome with a broader clinical phenotype (either milder or more severe than classic Rett syndrome) to mild learning disabilities; the spectrum in males ranges from severe neonatal encephalopathy to pyramidal signs, parkinsonism, and macroorchidism (PPM-X) syndrome to severe syndromic/nonsyndromic intellectual disability.

• Females: Classic Rett syndrome, a progressive neurodevelopmental disorder primarily affecting girls, is characterized by apparently normal psychomotor development during the first six to 18 months of life, followed by a short period of developmental stagnation, then rapid regression in language and motor skills, followed by long-term stability. During the phase of rapid regression, repetitive, stereotypic hand movements replace purposeful hand use. Additional findings include fits of screaming and inconsolable crying, autistic features, panic-like attacks, bruxism, episodic apnea and/or hyperpnea, gait ataxia and apraxia, tremors, seizures, and acquired microcephaly.
• Males: Severe neonatal-onset encephalopathy, the most common phenotype in affected males, is characterized by a relentless clinical course that follows a metabolic-degenerative type of pattern, abnormal tone, involuntary movements, severe seizures, and breathing abnormalities. Death often occurs before age two years.

Diagnosis/testing.

The diagnosis of a MECP2 disorder is established by molecular genetic testing in a female proband with suggestive findings and a heterozygous MECP2 pathogenic variant, and in a male proband with suggestive findings and a hemizygous MECP2 pathogenic variant.

Management.

Treatment of manifestations: Treatment is mainly symptomatic and focuses on optimizing the individual's abilities using a multidisciplinary approach that should also include psychosocial support for family members. Risperidone may help in treating agitation; melatonin can ameliorate sleep disturbances. Treatment of seizures, constipation, gastroesophageal reflux, scoliosis, prolonged QTc, and spasticity as per standard care.

Surveillance: Periodic evaluation by the multidisciplinary team; regular assessment of QTc for evidence of prolongation; regular assessment for scoliosis.

Agents/circumstances to avoid: Drugs known to prolong the QT interval.

Genetic counseling.

MECP2 disorders are inherited in an X-linked manner. More than 99% are simplex cases (i.e., a single occurrence in a family), resulting from a de novo pathogenic variant or possibly from inheritance of the pathogenic variant from a parent who has germline mosaicism. Rarely, a MECP2 variant may be inherited from a heterozygous mother in whom favorable skewing of X-chromosome inactivation results in minimal to no clinical findings. When the mother is a known heterozygote, the risk to her offspring of inheriting the MECP2 variant is 50%. When the pathogenic MECP2 variant has been identified in the family, heterozygote testing for at-risk female relatives, prenatal testing for pregnancies at increased risk, and preimplantation genetic diagnosis are possible. Because of the possibility of parental germline mosaicism, it is appropriate to offer prenatal diagnosis to couples who have had a child with a MECP2 disorder regardless of whether the MECP2 pathogenic variant has been detected in a parent.

Suggestive Findings in Females

A MECP2 disorder should be suspected/considered in females with the following clinical findings suggestive of MECP2 classic Rett syndrome or variant Rett syndrome (based on clinical diagnostic criteria published by Neul et al [2010] [full text] prior to the widespread availability of molecular genetic testing), or mild learning disabilities.

Clinical findings of MECP2 classic Rett syndrome and variant Rett syndrome

• Most distinguishing finding: A period of regression (range: ages 1-4 years) followed by recovery or stabilization (range: ages 2-10 years; mean: age 5 years)
• Main findings
  • Partial or complete loss of acquired purposeful hand skills
  • Partial or complete loss of acquired spoken language or language skill (e.g., babble)
  • Gait abnormalities: impaired (dyspraxic) or absence of ability
  • Stereotypic hand movements including hand wringing/squeezing, clapping/tapping, mouthing, and washing/rubbing automatisms
• Supportive findings
  • Breathing disturbances when awake
  • Bruxism when awake
  • Impaired sleep pattern
  • Abnormal muscle tone
  • Peripheral vasomotor disturbances
  • Scoliosis/kyphosis
  • Growth retardation
  • Small, cold hands and feet
  • Inappropriate laughing/screaming spells
  • Diminished response to pain
  • Intense eye communication - "eye pointing"
• Exclusionary findings
  • Brain injury secondary to peri- or postnatal trauma, neurometabolic disease, or severe infection that causes neurologic problems
  • Grossly abnormal psychomotor development in the first six months of life, with early milestones not being met

Clinical findings of MECP2 mild learning disability. Typically mild and non-progressive. Note: Typically, females with mild learning disability are identified through molecular genetic testing following diagnosis of a first-degree relative (e.g., a more significantly affected brother or sister).

Suggestive Findings in Males

MECP2 disorders should be considered in a male with severe neonatal encephalopathy; pyramidal signs, parkinsonism, and macroorchidism (PPM-X) syndrome; or syndromic/nonsyndromic intellectual disability.

Clinical findings of MECP2 severe neonatal encephalopathy

• Microcephaly
• Relentless clinical course that follows a metabolic-degenerative type of pattern
• Abnormal tone
• Involuntary movements
• Severe seizures
• Breathing abnormalities (including central hypoventilation or respiratory insufficiency)

Clinical findings of MECP2 severe intellectual disability (including PPM-X syndrome)

• Moderate-to-severe intellectual disability
• Resting tremor
• Slowness of movements
• Ataxia
• PPM-X syndrome: pyramidal signs, parkinsonism, and macroorchidism
• No seizures or microcephaly
• Usually normal brain MRI, EEG, EMG, and nerve conduction velocity studies

Establishing the Diagnosis

Female proband. The diagnosis of a MECP2 disorder is usually established in a female proband with suggestive findings and a heterozygous pathogenic variant in MECP2 identified by molecular genetic testing (see Table 1).

Male proband. The diagnosis of a MECP2 disorder is established in a male proband with suggestive findings and a hemizygous pathogenic variant in MECP2 identified by molecular genetic testing (see Table 1).

Molecular genetic testing approaches can include a combination of gene-targeted testing (either single-gene or multigene panel) or comprehensive genomic testing (exome sequencing, exome array, genome sequencing) depending on the phenotype.

Gene-targeted testing requires that the clinician determine which gene(s) are likely involved, whereas genomic testing does not. Because the phenotype of MECP2 disorders is broad, females with the distinctive findings described in Suggestive Findings are likely to be diagnosed using gene-targeted testing (see Option 1), whereas females and males with a phenotype indistinguishable from many other inherited disorders with intellectual disability and/or neonatal encephalopathy are more likely to be diagnosed using genomic testing (see Option 2).

Clinical Description

In females the spectrum of MECP2-related phenotypes ranges from classic Rett syndrome, to variant Rett syndrome (either milder or more severe than classic Rett syndrome), to mild learning disabilities. In males the spectrum ranges from severe neonatal encephalopathy, to pyramidal signs, parkinsonism, and macroorchidism (PPM-X) syndrome, to severe syndromic/nonsyndromic intellectual disability.