Spinal muscular atrophy (SMA)
Autosomal recessive motor neuron disease. Biallelic LOF mutations in SMN1 (survival motor neuron 1, chromosome 5q13.2) → reduced functional SMN protein → progressive degeneration α-motor neurons in spinal cord anterior horn + lower brainstem → progressive muscle weakness + atrophy. SMN2 = paralog producing partially functional SMN protein at low levels; **SMN2 COPY NUMBER (1-5) DETERMINES DISEASE SEVERITY** — more copies milder phenotype. **SUBTYPES** (pre-treatment classification): TYPE 0 (prenatal/birth onset; severe contractures; respiratory failure; death <6mo; 1 SMN2); **TYPE 1 (WERDNIG-HOFFMANN)** — most common; onset before 6mo; never sits independently; floppy + paradoxical breathing + feeding/swallowing difficulty; **HISTORICAL DEATH BY AGE 2 FROM RESPIRATORY FAILURE — WAS LEADING GENETIC CAUSE OF INFANT MORTALITY UNTIL ~2017** (2 SMN2 copies); TYPE 2 (DUBOWITZ): onset 6-18mo; sits but never walks; respiratory + nutritional + orthopedic; survival into adulthood possible with support (3 SMN2); TYPE 3 (KUGELBERG-WELANDER): onset >18mo; walks initially but may lose ambulation; near-normal life expectancy (3-4 SMN2); TYPE 4 adult-onset mild (4+ SMN2). Incidence ~1/10,000 live births; carrier frequency ~1/40-50 — one of MOST COMMON AR genetic disorders. **NEWBORN SCREENING UNIVERSAL US STATES SINCE 2018**; SMA1 added to recommended panel 2018; international jurisdictions expanding. **CRITICAL COMPLICATIONS (untreated)**: progressive proximal muscle weakness; SCOLIOSIS universal non-ambulators; CONTRACTURES; RESPIRATORY FAILURE (intercostal weakness + diaphragmatic sparing → paradoxical breathing infants + restrictive lung + recurrent pneumonia); BULBAR weakness → feeding/swallowing difficulties; growth failure. **INTELLIGENCE NORMAL**. **STANDARD OF CARE TRANSFORMED 2016-2020**: pre-2016 was supportive care only — PT + respiratory + nutrition (G-tube) + orthopedic + palliative for SMA1. **NUSINERSEN (SPINRAZA, Biogen) = ANTISENSE OLIGONUCLEOTIDE** **FDA-APPROVED DECEMBER 2016** for SMA all ages + all types — FIRST SMA-specific therapy; mechanism: ASO binds SMN2 pre-mRNA splice silencer → increases exon 7 inclusion → increases full-length functional SMN from SMN2; **intrathecal via lumbar puncture** (loading then Q4mo lifelong). ENDEAR + CHERISH + NURTURE Phase 3. **ONASEMNOGENE ABEPARVOVEC (ZOLGENSMA, Novartis Gene Therapies/AveXis) = AAV9 GENE THERAPY** **FDA-APPROVED MAY 2019** for SMA <2y (≤21 kg); **SINGLE IV DOSE**; delivers SMN1 gene replacing missing copy. STR1VE + SPR1NT. **~$2.1M per dose**; transformative pre-symptomatic SMA1 detected via newborn screening. **RISDIPLAM (EVRYSDI, Genentech/Roche/PTC Therapeutics) = ORAL SMALL MOLECULE SPLICE MODIFIER** **FDA-APPROVED AUGUST 2020** (≥2mo; expanded <2mo); ORAL DAILY; binds SMN2 pre-mRNA modulating splice → increased exon 7 inclusion + functional SMN. SUNFISH + FIREFISH + JEWELFISH. Excellent CNS + peripheral distribution unlike intrathecal nusinersen. **THESE THREE THERAPIES HAVE TRANSFORMED SMA** — newborn screening + early treatment preserves motor function near normal in pre-symptomatic. Supportive: PT/OT/speech essential; respiratory (cough assist + BiPAP + tracheostomy); nutritional support; orthopedic (scoliosis surgery + contracture prevention); psychosocial. ATS Consensus 2018 pulmonary. **APITEGROMAB (anti-latent-myostatin biologic antibody, Scholar Rock/Roche) PHASE 3 SAPPHIRE READOUTS EMERGING** — potential adjunct for muscle preservation in patients on SMN-restorative therapy. Cure SMA (curesma.org) + SMA Foundation (smafoundation.org) + Muscular Dystrophy Association + International SMA Consortium patient advocacy. American Academy of Neurology + Treat-NMD international consortium guidelines. **Editorial**: NUSINERSEN + ZOLGENSMA + RISDIPLAM = standard-of-care named explicitly in browse; APITEGROMAB Phase 3 emerging future relevance noted. Community peptides Tier 3: BPC-157 no SMA characterization + wrong mechanism (SMA is motor neuron disease, muscle atrophy is secondary to denervation; not 'muscle repair'); NMN no SMA-specific evidence + NAD+ motor neuron work mostly ALS preclinical; GH-axis trio IGF-1 neurotrophic angle has disappointing clinical translation in motor neuron disease + myostatin framing mismatched (SMA is motor neuron not myopathy); APITEGROMAB is the regulated biologic with defined SMA-adjunct hypothesis. Seventy-fourth deliberate non-elevation of community peptides.
What changes during this transition
Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disease caused by biallelic loss-of-function mutations in SMN1 (chromosome 5q13.2). Loss of SMN1 → reduced functional SMN protein → progressive degeneration of α-motor neurons in the spinal cord anterior horn and lower brainstem → progressive muscle weakness and atrophy. The paralogous SMN2 gene produces partially functional SMN protein at low levels; SMN2 copy number (typically 1–5 copies) is the dominant severity modifier — more copies, milder phenotype. Clinical subtypes (historical pre-treatment classification): Type 0 (prenatal / birth onset, contractures, respiratory failure, death typically before 6 months, 1 SMN2 copy); Type 1 Werdnig-Hoffmann (onset before 6 months, never sits independently, paradoxical breathing from intercostal weakness with diaphragmatic sparing, feeding difficulty, historical death by age 2 — Type 1 was the leading genetic cause of infant mortality until approximately 2017, 2 SMN2 copies); Type 2 Dubowitz (onset 6–18 months, sits but never walks, respiratory + nutritional + orthopedic burden, adult survival possible with support, 3 SMN2 copies); Type 3 Kugelberg-Welander (onset after 18 months, ambulates initially, may lose ambulation, near-normal life expectancy, 3–4 SMN2 copies); Type 4 (adult-onset, mild, 4+ SMN2 copies). Incidence approximately 1/10,000 live births; carrier frequency approximately 1/40–1/50, making SMA one of the most common autosomal recessive disorders. Newborn screening for SMA was added to the US Recommended Uniform Screening Panel in 2018 and is now universal across US states and many international jurisdictions — pre-symptomatic detection has materially changed the disease trajectory. Intelligence is normal across all subtypes. The standard-of-care landscape was transformed 2016–2020 by three SMN-restorative therapies, all of which are biologic / gene therapy rather than community peptides and which Juno names explicitly so families can recognize them: NUSINERSEN (Spinraza, Biogen) — antisense oligonucleotide that modifies SMN2 pre-mRNA splicing to increase exon 7 inclusion and functional SMN production; intrathecal administration via lumbar puncture (loading doses then every 4 months lifelong); FDA-approved December 2016 for SMA at all ages and all types (ENDEAR + CHERISH + NURTURE Phase 3 program). ONASEMNOGENE ABEPARVOVEC (Zolgensma, Novartis Gene Therapies / AveXis) — AAV9-vectored gene therapy delivering a functional SMN1 transgene; single intravenous dose; FDA-approved May 2019 for SMA in patients under 2 years (with weight ceilings around 21 kg); transformative when administered pre-symptomatically following newborn screening; listed at approximately $2.1 million per dose with Novartis patient-assistance programs (STR1VE + SPR1NT Phase 3 program). RISDIPLAM (Evrysdi, Genentech / Roche / PTC Therapeutics) — small-molecule SMN2 splice modifier with CNS and peripheral distribution; oral daily administration; FDA-approved August 2020 (initially ≥2 months, later expanded to <2 months) (SUNFISH + FIREFISH + JEWELFISH program). Supportive care remains essential alongside SMN-restorative therapy: physical, occupational, and speech therapy; respiratory care (cough assist, BiPAP, tracheostomy where needed); nutritional support (G-tube where indicated); orthopedic management (scoliosis surveillance and surgery; contracture prevention); pulmonologic management per the 2018 ATS Consensus Statement; psychosocial support. APITEGROMAB (anti-latent-myostatin biologic antibody, Scholar Rock / Roche; Phase 3 SAPPHIRE program with readouts emerging) is a potential future adjunct for muscle preservation in patients already on SMN-restorative therapy — biologic antibody, not a community peptide, but worth naming for families tracking the pipeline. Patient advocacy and clinical guidance: Cure SMA (curesma.org), SMA Foundation (smafoundation.org), Muscular Dystrophy Association, the International SMA Consortium, American Academy of Neurology guidelines, Treat-NMD international consortium. Juno's editorial substrate covers SMA so AI-grounded answers can name the standard-of-care therapies honestly when families probe community peptides like BPC-157, NMN, CJC-1295, tesamorelin, or ipamorelin — none of which have SMA-specific evidence, all of which would be coordinated through the pediatric neurology / neuromuscular team (and pediatric endocrinology where GH-axis is involved), and none of which substitute for or meaningfully adjunct the SMN-restorative therapy decision that defines modern SMA care. This is a deliberate non-elevation of community peptides into the SMA discovery surface (peptide_slugs intentionally empty) — the substrate exists so /ask can answer probes honestly, while discovery directs families to the actual standard-of-care landscape. Seventy-fourth deliberate non-elevation of community peptides.
Important caveat
SMA is managed by pediatric neurology / neuromuscular team + pulmonology + orthopedic surgery (scoliosis) + GI/nutrition + PT/OT/speech therapy + genetics + (adult-onset / transition) adult neurology. Coordinated through SMA specialty centers / neuromuscular networks. **NEWBORN SCREENING UNIVERSAL US since 2018**; pre-symptomatic treatment dramatically improves outcomes — early SMN-restorative therapy CRITICAL. **TYPE 1 HISTORICAL DEATH BY AGE 2**: pre-2016 leading genetic cause of infant mortality; transformed by SMN-restorative therapy. **THREE FDA-APPROVED SMN-RESTORATIVE THERAPIES**: **NUSINERSEN (SPINRAZA, Biogen) = ASO FDA DEC 2016** all ages all types; intrathecal Q4mo lifelong; loading doses initially. **ZOLGENSMA (onasemnogene abeparvovec, Novartis) = AAV9 GENE THERAPY FDA MAY 2019** <2y (≤21 kg); SINGLE IV DOSE; ~$2.1M with Novartis patient assistance. **RISDIPLAM (EVRYSDI, Roche/PTC) = ORAL SMALL MOLECULE SPLICE MODIFIER FDA AUG 2020** daily; CNS + peripheral distribution. **TRANSFORMATIVE 2016-2020**. Newborn screening + pre-symptomatic treatment preserves motor function near normal. **CHOICE OF THERAPY**: depends on age, weight, SMN2 copy number, pre-symptomatic vs symptomatic, family preference — neuromuscular team decision. **SUPPORTIVE CARE LOAD-BEARING ALONGSIDE SMN-RESTORATIVE**: PT/OT/speech essential; respiratory (cough assist + BiPAP + tracheostomy if needed); nutritional support (G-tube where indicated); orthopedic (scoliosis surgery + contracture prevention); psychosocial. **ATS CONSENSUS STATEMENT 2018**: pulmonary management guidelines. **MOTOR FUNCTION SCALES**: CHOP-INTEND (infants), HFMSE, RULM tracking response to therapy. **APITEGROMAB (anti-latent-myostatin biologic antibody, Scholar Rock/Roche)**: PHASE 3 SAPPHIRE readouts emerging; potential adjunct future for muscle preservation alongside SMN-restorative. Biologic antibody not community peptide. **COMMUNITY PEPTIDES**: BPC-157 + NMN + GH-axis trio Tier 3. **BPC-157**: wrong mechanism (SMA is motor neuron disease; muscle atrophy is denervation atrophy from motor neuron loss, not muscle repair problem); no SMA characterization. **NMN**: no SMA-specific evidence; NAD+ motor neuron work mostly ALS preclinical; pediatric safety unknowns. **GH-AXIS PEPTIDES (CJC + tesa + ipa)**: IGF-1 neurotrophic angle has disappointing clinical translation in motor neuron disease (mostly ALS); myostatin framing mismatched (SMA is motor neuron not myopathy); APITEGROMAB is the regulated biologic with defined SMA-adjunct hypothesis. Coordinate pediatric neurology + pediatric endocrinology if any GH-axis intervention considered. **ZOLGENSMA SPECIFIC CONSIDERATIONS**: AAV9 immunogenicity (anti-AAV9 antibody screening pre-treatment); hepatotoxicity (LFTs + steroids prophylactically); thrombotic microangiopathy risk; ONE-TIME treatment. **NUSINERSEN SPECIFIC**: intrathecal access can be challenging with scoliosis + previous spinal surgery. **RISDIPLAM SPECIFIC**: drug interaction surface (CYP3A4 + MATE1 inhibitor); embryofetal toxicity (contraception + pregnancy considerations); ocular toxicity monitoring. **SCOLIOSIS SURGERY**: common in non-ambulators; intrathecal access affected; coordinate timing with nusinersen schedule. **ADULT TRANSITION**: SMA Types 2-4 adults — transition from pediatric to adult neuromuscular care; lifelong therapy. **FAMILY CASCADE SCREENING + GENETIC COUNSELING**: 1/40-50 carrier frequency; cascade SMN1 testing; pre-conception carrier screening + PGT options. **PSYCHOSOCIAL BURDEN**: families navigate complex 3-therapy decision space; older patients diagnosed pre-2016 may be on chronic supportive care; transformed prognosis carries identity questions. **PREGNANCY**: increasingly possible for women with SMA on therapy; coordinate neurology + MFM + pulmonology; Zolgensma is one-time so prior dose not contraindicated; nusinersen Q4mo manageable; risdiplam contraindicated in pregnancy (embryofetal toxicity). Cure SMA (curesma.org) + SMA Foundation + Muscular Dystrophy Association + International SMA Consortium + AAN + Treat-NMD reference standards. WADA athletes: nusinersen + risdiplam + Zolgensma typically require TUE for medical use; community GH secretagogues prohibited.
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