Is MECP2 p.Pro277= (c.831C>G) pathogenic?

MECP2 p.Pro277= (c.831C>G) is classified Benign/Likely benign in MECP2 (ClinVar, Multiple submitters, 4 submitters; last evaluated 2025-05-30). Ultra-rare (popmax 0.051%, sas); Associated with severe neonatal-onset encephalopathy with microcephaly.

What condition is associated with MECP2 p.Pro277= (c.831C>G)?

MECP2 p.Pro277= (c.831C>G) is associated with severe neonatal-onset encephalopathy with microcephaly, Rett syndrome (ClinVar).

How common is MECP2 p.Pro277= (c.831C>G) in the general population?

MECP2 p.Pro277= (c.831C>G) is ultra-rare (popmax 0.051%, sas) (gnomAD).

How is MECP2-related severe neonatal encephalopathy inherited?

Typically X-linked recessive (Orphanet). A genetic counselor can assess individual risk for a family.

MECP2 p.Pro277=

c.831C>G · rs267608527 · VCV143698

Benign/Likely benign Multiple submitters

Classification

Benign/Likely benign

ClinVar

Review

Multiple submitters ★★☆☆

ClinVar · 4 submitters

gnomAD v4.1

Rare

ultra-rare (popmax 0.051%, sas)

Conditions

severe neonatal-onset encephalopathy with microcephaly

Computational evidence

Protein change
Missense predictors do not apply to this variant type; conservation carries the signal.
Splicing
SpliceAI	—	not assessed · no allele here is in the release
Constraint at this position
Conservation	phyloP 1.9	GERP 0.17, phastCons 1
Overall
CADD	8.044	PHRED · no single calibrated threshold — expert panels disagree

Population frequency

gnomAD v4.1 · exomes + genomes

Grpmax group 0.051% South Asian · 29/56,911 alleles

Filtering AF 0.0364% ClinGen BA1/BS1 input FAF95, joint · FAF99 0.0315%

Overall 0.00281% 34/1,210,797 alleles · ultra-rare exomes 32/1,098,139 · genomes 2/112,658 · joint denominator

Ancestry group	Frequency	1 in
South Asiangrpmax	0.051%	1,962
Finnishnot grpmax-eligible	0.00214%	46,703
African / African-American	0.00174%	57,401
European (non-Finnish)	0.000335%	298,443

Rarity supports pathogenicity (ACMG PM2); frequency above a disease-specific BA1/BS1 threshold argues against it. A variant frequent in one ancestry group can be near-absent in others, so a single global figure can mislead.

Variant & gene context

Gene: MECP2
Protein: p.Pro277=
Coding: c.831C>G
MANE Select: NM_001110792
dbSNP: rs267608527
Type: single nucleotide variant
Location: chrX:154031033 (GRCh38)
Structure: AlphaFold pLDDT 57.25 · 11 PDB
Residue 277: a DNA-binding region; the 'interaction with ncor2' region; a UniProt-annotated variant site (in rtt)

Full MECP2 gene report on Sugi Atlas → Gene function, pathways, protein structure, interactions & more

Disease context

severe neonatal-onset encephalopathy with microcephaly — disease report on Sugi Atlas → Associated genes, phenotypes, clinical trials & treatments

Also linked: Rett syndrome

For MECP2-related severe neonatal encephalopathy (Orphanet):

Inheritance: X-linked recessive
Onset: Infancy, Neonatal

Similar variants

MECP2 p.Pro277His Uncertain significance ★ ⚠ same residue
MECP2 p.Pro277fs Likely pathogenic ★ same residue
MECP2 c.414-3C>G Pathogenic ★★★ same condition
MECP2 c.62+1G>A Pathogenic ★★★ same condition
MECP2 c.62+2T>G Pathogenic ★★★ same condition
MECP2 p.Ala143Asp Pathogenic ★★★ same condition
MECP2 p.Ala291Val Likely pathogenic ★★★ ⚠ same condition
MECP2 p.Arg127His Pathogenic ★★★ same condition

Built on 18 open, versioned datasets — ClinVar, gnomAD, AlphaMissense, REVEL, ClinGen & more — plus Sugi Variant's own cross-source analysis. Source data 2026-01–2026-10, ClinVar 2026-10. Full sources & versions →

Cite Sugi Variant

Gür T. Sugi Variant: A Deterministic Per-Variant Germline Reference from a Knowledge Graph for Humans and AI Agents. 2026. doi:10.5281/zenodo.21509445. This variant: https://sugi.bio/variant/mecp2-p-pro277 (accessed [today's date]).

Preprint & method: sugi.bio/variant/method Machine-readable: this page as Markdown